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Electronics Laboratory for the Physical Sciences

I.M.S. De Vera, M.J. M. Garrovillas and E.T. Chainani

Resistors

Objectives

(1) To become familiar with the resistor color code and the use of

the digital multimeter (DMM) as an ohmmeter.

(2) To become familiar with a variable resistor (potentiometer).

(3) To determine how the resistance of a thermistor varies with

temperature.

Components needed:

Assorted 4-band and 5-band resistors Digital Multimeter

Potentiometer Thermistor

The Resistor

The resistor is the most common component in electronics. A

resistor is a two-terminal electrical or electronic component that

opposes an electric current by producing a voltage drop between its

terminals in proportion to the current. Resistors measure resistance, the

ratio of the degree to which an object opposes an electric current

through it. Resistance is measured in units called ohms () to honor

Georg Simon Ohm (1787-1854), a German physicist credited for

formulating the current-voltage relationship for a resistor (V = IR, Ohms

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Law). According to Ohms Law, the resistance R is equals to the voltage

drop V across the resistor divided by the current I through the resistor.

The symbols for fixed resistors and variable resistors are shown

respectively, followed by a picture of an actual resistor showing the

color code (Figure 1):

Figure 1. Resistor symbols and color code.

Fixed resistors usually come in two types: the 4-band resistor and

the 5-band resistor. The primary difference the two is the number of

color bands appearing in them. Both types, a resistor color code is used

to identify the nominal values of the resistance.

For 4-band resistors, the resistor color code is given in Table 1 below.

Table 1. 4 Band Resistor color code

Color1st color

band (firstdigit - a)

2nd color band(second digit - b)

3rd colorband

(exponent - c)

4th color band(tolerance - d)

Black 0 0 0Brown 1 1 1 1%

Red 2 2 2 2%Orange 3 3 3 3%Yellow 4 4 4 4%Green 5 5 5Blue 6 6 6Violet 7 7 7Gray 8 8 8White 9 9 9

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Gold -1 5%Silver -2 10%

No color 20%

The resistor color code is used to identify the nominal values of the

resistance as follows:

4-Band Resistors: The first two colored bands (a & b, closest to

the end of the resistor in Figure 1) determine the first two digits

of the resistor value. Table 1 shows the listing of the numerical

value associated with each color. The third band (c) determines

the exponent of the power-of-10 multiplier i.e. the number of

zeros following the first 2 digits. The fourth band (d)

determines the tolerance of the resistor.

Resistance = (10a + b) x 10c d

For example, a 21 kiloohm 5% resistor has the color bands red,brown, red, and gold. Common prefixes used for resistors arekilo(k) and mega (M).

For 5-band resistors, the resistor color code is given in Table 1 below.

Table 2. 5-Band Resistor Color Code

Color 1st colorband, firstdigit (a)

2nd colorband,seconddigit (b)

3rd colorband,thirddigit (c)

4th colorband,exponent(d)

5th colorband,tolerance(e)

Black 0 0 0 0Brow 1 1 1 1 1%Red 2 2 2 2 2%

Orange 3 3 3 3 3%Yellow 4 4 4 4 4%Green 5 5 5 5Blue 6 6 6 6Violet 7 7 7 7Gray 8 8 8 8White 9 9 9 9Gold -1 5%

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Silver -2 10%No Color 20%

5-Band Resistors: The first three colored bands (a, b, and c,

first three of the four adjacent color bands), determine the firstthree digits of the resistor value. The fourth band (d)

determines the exponent of the power-of-10 multiplier, i.e., the

number of zeros following the first two digits. The fifth band (e),

the color band farthest from the four adjacent color bands,

determines the tolerance of the resistor. Thus,

Resistance = (100a + 10b + c) x 10d e

For example, an 82.5 kiloohm 1% resistor has the color bands gray,

red, green, red, and brown.

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Measuring Technique

Resistance is never measured in a live circuit using a DMM because the resistor

might be damaged. The resistor to be measured should be removed from the circuit to

ensure that your measurement will not be affected by any other components of the circuit.

Make sure also that when you measure the resistor, only the probes of the DMM are

touching the resistor. In other words, avoid touching the resistor as much as possible.

There is no calibration for the DMM. Short (connect) the leads together and the

DMM should display zeros (or less than 0.3 ohms). Any resistance above the maximum for

a selected scale will result in the display showing 1 or OL or sometimes constantly

fluctuating. Adjust the DMM to the correct scale.

Exercise

A.Nominal vs. Actual Resistance

Get five different resistors from your instructor. Record the nominal resistance of

the resistors (based on Tables 1 or 2, depending on the number of color bands), the actual

resistance (based on the DMM reading), and the percent discrepancy between the nominal

and actual resistance readings of each resistor. Calculate for the minimum and maximum

tolerance resistance by subtracting or adding a specific amount based on the tolerance of

the resistor. Actual Tolerance is difference of actual from nominal resistance.

Ex: For a 12 kiloohm 5% resistor (brown, red, orange, gold color code) has a

maximum tolerance resistance of [12,000 + (12,000 *.05)] kiloohm = 12.6 kiloohm. It has

a minimum tolerance of [12,000 - (12,000 *.05)] kiloohm = 11.4 kiloohm.

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Compute % Discrepancy as:

B. Potentiometer

Get a variable resistor / potentiometer from your instructor. The resistance of the

potentiometer varies by twisting its knob. Determine the maximum and minimum

resistance values of your potentiometer by twisting the knob to the left and right.

To measure, attach the middle wire of the potentiometer to the ground probe (black)

of the DMM. After this, attach either left or right wire of the potentiometer to the positive

probe (red) of the DMM. Refer to Figure 2 below:

Figure 2: How to Measure Resistance from the Potentiometer

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C. Thermistor

Get a thermistor from your instructor. The resistance of the thermistor varies with

respect to temperature.

First, get the resistance of the thermistor in an air-conditioned room. Record the

resistance reading as Raircon. Measure the temperature of the room and record it as Taircon.

Second, clamp the thermistor tightly between two fingers. Get the resistance of the

thermistor after 5 to 10 minutes. Record the resistance reading as Rbody. Clamp the

thermometer between your fingers and measure the temperature and record it as Tbody.

Lastly, get the resistance of the thermistor outside of the air-conditioned room.

Equilibrate for at least 10 minutes. Record the resistance reading as Routside. Measure the

temperature outside the room and record it as Toutside.

Using the obtained Raircon, Rbody, Taircon, and Tbody, construct a two-point calibration

curve using MS Excel or linear regression from a scientific calculator. From the recorded

Routside, solve for Toutside, theoretical using the equation derived from the calibration curve.

Compare the computed value to the recorded Toutside and solve for the %difference:

Obtain the slope of the line to solve forR/T which has units of (/C)

Sources:

(1) Oppus, C.M. PS 141 Laboratory Manual. 2nd ed, 2003.

(2) Malmstadt, H.V.; Enke, C.G.; Crouch, S.R. Laboratory Electronics for

Scientists, 2nd Ed., 1994.

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Resistors

Group Name: ________________________ Section: ________

Name: ______________________________

Raw Data Tables:Resistor Color Code Nominal R % Tolerance

1

2

3

4

5

Derived Data Tables:

Resistor

Actual

Tolerance

R

Min.

Tolerance RMax. Tolerance R Actual R

%

Discrepancy

1

2

3

4

5

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B.

Maximum Resistance of Potentiometer: ____________________

Minimum Resistance of Potentiometer: ____________________

C.

Resistance Temperature

Air-conditioned room

Body

Toutside, theoretical: ______ Toutside, derived:______ %difference: __________

Routside: ____________R/T = _________

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1. Why is it necessary that only the probes of the DMM are touching the resistor?

2. How does the thermistor resistance change with temperature? How would you

describe its temperature coefficient?

3. (For out-of-classroom research) How is a potentiometer constructed? What are the

three terminals of the potentiometer for?

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The Breadboard

Objectives

(1) To become familiar with the uses of a breadboard.

(2) To determine the connection arrangement of a breadboard.

Components needed:

Breadboard Digital Multimeter

The Breadboard

The breadboard is used to create a circuit without the need for

soldering circuit elements together. The upper and lower halves of the

breadboard contain 64 vertical rows of 5 interconnected contacts. There

are also 4 long horizontal rows of connectors (5 groups of 5 contacts

each) along the upper and lower edges. These long rows of connectors

are referred to as power bus strips because they will be connected to

the power supplies to provide power connections over the entirety of the

breadboard. This breadboard socket is designed to accept integrated

circuits, most common wire terminal components, and wire

interconnections.

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Exercise

Switch the DMM to measure resistance (any scale will do). Again,

keep in mind that a short circuit gives a reading of 0 while an open

circuit gives a reading of infinite resistance (1 or 0L).

Insert wires into the breadboard holes carefully. Grasp the wire

with your hands about inch from the end to be inserted and push into

the breadboard until it is firmly in place.

Figure 1. The Breadboard.

Use the DMM to confirm the connection arrangement of the breadboard.

Draw the verified connection arrangement of the breadboard given to

you in the space below.

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Source:

(1) Malmstadt, H.V.; Enke, C.G.; Crouch, S.R. Laboratory Electronics

for Scientists 2nd Ed. 1994.

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Power Supply

Objectives

(1) To connect a regulated power supply to the breadboard.

(2) To differentiate between regulated and unregulated power

supplies.

Components needed:

Breadboard Digital Multimeter

Power Sockets (2)

Jumper wires 100 1-W resistors (2)

0.1 uF ceramic capacitor

1 uF tantalum capacitor 2.2 or 3.3 uf tantalum or electrolytic capacitors

Voltage regulators (7805 and 7905)

Exercise

A. Unregulated Power Supply

Install the two power supply sockets into the breadboard as shown

below (Figure 1). Also attach the wires as shown in the diagram. The

wire colors are not necessary; they are just a useful reminder of what

each line is carrying (red = positive, yellow = negative, black =

ground/common).

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Figure 1. Installing the power supply sockets.

Plug one adapter into one of the sockets. Using the DMM, measure

the voltage between the red and black power buses. This should be

around 9-12 V. This is the DC output voltage without load. Keep in mind

however that the DMM has an internal 10 M resistance.

An unregulated power supply will have a fluctuating output

voltage depending on the load connected to it.

Connect two 100 1-W resistors in series. Connect one end to the

power supply and the other end to ground. Again, measure the output

voltage.

Disconnect the power supply. Are the resistors hot?

B. Creating a Regulated Power Supply

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Figure 2. Schematic diagram for the regulated power

supply.

To regulate the voltage output of the unregulated power source, one

uses a full-wave rectifier-filter circuit, as shown in Figure 2. In your

breadboard, add the circuit elements as shown in Figures 3 and 4. Make

sure that you follow the polarities of the capacitors. The longer wire of

the capacitor is the positive end. The capacitors are added to prevent

noise and oscillation and to increase the stability of the output voltage.

C

Figure 3 Figure 4

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Connect the voltmeter across the red and black power buses. Plug

the power supply to the positive power socket. Disconnect immediately

if the voltage is not within 5% of +5 V or if the regulator becomes hot.

Record the positive regulated voltage without load.

Now connect the voltmeter across the yellow and black power

buses. Plug the power supply to the negative power socket. Disconnect

immediately if the voltage is not within 5% of 5 V or if the regulator

becomes hot. Record the negative regulated voltage without load.

Connect two 100 1-W resistors in series. Connect one end to the

positive regulated power supply and the other end to ground. Measure

the output voltage with load. Compare this to the data you got earlier.

The regulators will become hot so do not keep the connections for long

periods.

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Source:

(1) Malmstadt, H.V.; Enke, C.G.; Crouch, S.R. Laboratory Electronics

for Scientists 2nd Ed. 1994.

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Power Supply

Group Name: _________________

Name: ______________________________

A.

Unregulated voltage output without load: __________

Unregulated voltage output with load: __________

B.

Regulated voltage output without load: __________

Regulated voltage output with load: __________

1. What is the purpose of regulating the power supply?

2. Explain briefly the process of converting the 220 V AC power

supply to the 5 V DC regulated power supply.

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Resistors in Series and Parallel

Objective

To become familiar with the different resistive connections

particularly parallel and series connections.

Components needed:

Regulated Power Supply from Experiment 3 Digital Multimeter

Assorted Resistors (3)

Series and Parallel

Series resistor configuration consists of two or more resistors

connected tail to head with the open terminals as the series connection

terminals as shown below (Fig. 1):

Figure 1. Resistors in series.

The effective resistance of resistors in series is equal to the sum of

their individual resistances:

=

=n

i

iequiv RR1

Equation 1

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Parallel resistor configuration consists of two or more resistors

connected tail to tail then head to head with the head connection

forming one of the terminals and the tail connection forming the other,

as shown below (Figure 2):

Figure 2. Resistors in parallel.

The inverse of the effective resistance of parallel resistors is equal

to the sum of the inverses of their individual resistances:

Exercises

Part A.

Get 3 different resistors from your instructor. With the concepts of

series and parallel circuits in mind, construct a circuit with your 3

resistors such that the minimum resistance value is obtained. Connect

this new resistor to the 5-V regulated power source (with the other

end connected to ground).

=

=n

i iequivRR 1

11 Equation

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Also, connect the multimeter in series with the new resistor. Get

the value of the current, I (make sure that the DMM is properly

configured). Using Ohms law (V = IR), youll be able to get the

experimental R. Using the appropriate equation, youll be able to get the

nominal R. Determine the % difference of the two values.

Disconnect the multimeter from the circuit but keep the circuit intact.

Read the voltage across each resistor by connecting the DMM in parallel

across each one (make sure that the DMM is properly configured). Also,

read the current flowing through each resistor by connecting the DMM in

series to each (again, make sure that the DMM is properly configured).

Part B.

Using the resistors you used earlier, construct a circuit such that the

maximum resistance is obtained. Connect this new resistor to the 5-V

regulated power source.

Connect the multimeter in series with this new resistor. Get the

value of I. With this value, get the experimental value of R. Compare this

with the nominal value of R of your circuit. Determine the % difference

of the two values.

Disconnect the multimeter from the circuit but keep the circuit intact.

Get the current through each resistor and the voltage across each

resistor using the DMM.

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Source:

(1) Oppus, C.M. PS 141 Laboratory Manual. 2nd

Ed, 2003.

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Resistors in Series and ParallelGroup Name: _________________Name: _______________________________

A. Icicruit:____________

Rnominal :___________ Rexpt:_____________ %

difference_____________

Vequivalent:__________

Resistor Resitance/ Voltage (V) Current (I)

Nomin

al

Actua

l

Calculate

d Actual

Calculat

ed

Actua

l

Calculat

edR1

R2

R3

Total

B. Icicruit:____________

Rnominal :___________ Rexpt:_____________ %

difference_____________

Vequivalent:__________

Resistor Resitance/ Voltage (V) Current (I)

Nomin

al

Actua

l

Calculate

d

Actual Calcula

ted

Actua

l

Calculat

edR1

R2

R3

Total

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1. What do you observe about the voltage across each resistor in A?

Add up all current values through each resistor. How is this related

to I of the whole circuit?

2. What do you observe about the current through each resistor in B?

Add up all the voltages of each resistor. How is this related to the

V of the whole circuit?

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3. Why is there a discrepancy between the nominal and experimental

values of resistances?

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Diodes

Objective

To become familiar with the uses of a diode.

Light-emitting diode

A diode is a device which allows the flow of current in a circuit in a

single direction. Ideally, the diode is just a conductor, i.e., it has zero

resistance. The circuit symbol of a light-emitting diode is shown below

(Figure 1):

Figure 1. Circuit symbol of a light-emitting diode.

A light-emitting diode (LED) follows that same principle. However,

it utilizes the current that passes through it to give off light.

Exercise

Part A

Construct the circuit shown in Figure 2. You may use wires to

make the switch, just connect or disconnect the wires as necessary.

Check your circuit by turning on the switch and checking the current on

the end of the diode connected to ground. If there is no current, invert

the position of your diode.

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Figure 2. Diode circuit.

What is the current? Is this the current that you expected with the

220 resistor?

Part B

Replace the diode with a light-emitting diode. If no light is emitted

by the LED, invert its position. Add more LEDs in series and in parallel

to the original LED in the circuit. What happens to the intensity of the

light of the LEDs?

Part C

Again, construct the circuit shown in Figure 1, but this time,

replace the resistor with a potentiometer and the diode with an LED.

Make sure you connect the potentiometer correctly, i.e., the resistance

varies as the knob is turned. Turn on the switch. What happens to the

intensity of the light of the LED when you turn the knob?

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Sources:

(1) http://stage.itp.nyu.edu/~tigoe/pcomp/labs/assign1.shtml

accessed March, 2003.

(2) Horowitz, P.; Hill, W.; The Art of Electronics. 2nd Ed. Cambridge

University Press, 1991.

Diodes

Group Name: _________________

Name: ______________________________

A.

Theoretical current : __________

Actual current: __________

Diode resistance: __________

1. How does adding more resistors and LEDs to the circuit affect the

intensity of the light? Does it matter whether the LEDs are

connected in series or in parallel?

29
http://stage.itp.nyu.edu/~tigoe/pcomp/labs/assign1.shtmlhttp://stage.itp.nyu.edu/~tigoe/pcomp/labs/assign1.shtmlhttp://stage.itp.nyu.edu/~tigoe/pcomp/labs/assign1.shtml

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2. How does resistance in series to the LED affect the intensity of the

light?

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Figure 1. The operational amplifier terminal diagram.



Operational Amplifiers

Objective

To become familiar with the different configurations of an

operational amplifier.

Materials

+5V/-5V power supply from Experiment 3

LF353 operational amplifier

1 or 2.5k potentiometer

Two 2.2k resistors

One 10k resistor

One 47k resistor

One 22k resistor

Digital multimeter

Two DC converters

Green or yellow LED

Dark cover for LED

Operational amplifier

The terminal diagram of an operational amplifier is shown below

(Figure 1).

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Figure 2. LF353 op-amp pin configuration



The operational amplifier amplifies the voltage across its two

inputs by a gain factor. The gain to which the input voltage difference is

amplified depends on the values of the feedback elements.

The operational amplifier that you will use for this exercise is the

LF353. The pin configurations are shown in Figure 2.

Exercise

A. Inverting amplifier

Construct the variable-voltage source using a 1 or 2.5k

potentiometer placed between two 2.2k resistors. One end of both

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resistors are then connected to the +5V/-5V power supply from

Experiment 3 as shown in Figure 3.

Figure 3. Op-amp Inverting Amplifier

Test that the variable voltage source can go from -1 to +1V as the

potentiometer knob is turned. This can be done by using a digital

multimeter. Connect one probe of the multimeter on the center terminal

of the potentiometer and the other one will be on one end of the

potentiometer.

The variable-voltage source will serve as the input for the op-amp

inverting amplifier. This will also be the voltage input, Vin, which will be

recorded.

On the breadboard, insert the op-amp integrated circuit (IC)across the center channel as shown in Figure 4. Consult Figure 3 to

construct the remaining parts of the circuit.

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Figure 4. Placing the op-amp onto the breadboard.

Vary Vin by turning the potentiometer knob from the maximum

allowable voltage to approximately 0.50V, 0.25V, 0.00V, -0.25V, -0.50V,

and the minimum allowable voltage. Record the voltage output, Vout,

together with the actual Vin. Vout can be acquired from the digital

multimeter readout.

B. LED as a light detector

Use an LED as a light detector together with an op-amp current-to-

voltage converter. Normally, an LED is used to emit light when current is

passed through it. However, when the LED is illuminated, it creates a

small current and can be used as a photodiode light detector.

Construct the circuit shown in Figure 5. Use only a yellow (preferred)

or a green LED. Do not use a red LED. You need to use only one op-amp

in the IC. NOTE: You must ensure that the LED is reverse-based. If the

LED lights up, reverse it.

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Figure 5. LED circuit diagram.

With the LED covered, measure the voltage output. Remove the

cover of the LED, exposing it to light. Again, measure the voltage output

of the operational amplifier.

Use an LED as a light detector together with an op-amp current-to-

voltage converter. Normally, an LED is used to emit light when current is

passed through it. However, when the LED is illuminated, it creates a

small current and can be used as a photodiode light detector.

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Source:

(1) Malmstadt H.V.; Enke, C.G.; Crouch, S.R. Laboratory Electronics

for Scientists 2nd

Ed. 1994.

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Operational Amplifiers

Group Name: _________________ Name:

______________________________

Part 1.

R1 (input): ____________ ohms R2 (feedback resistor):

___________ohms

Vin

(nominal)

Vin

(expt.)

Vout

(theoret.)

Vout

(expt.)

Gain (Vout / Vin)

-1.00-0.50-0.250.000.250.501.00

1. What is the value of gain and how does it relate to the values of R1

and R2?

2. The gain decreases as the op-amp output voltage approaches the

supply voltages. This is called saturation. What is the

approximate positive saturation voltage?__________ Negative

saturation voltage? ________________.

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Part 2.

Compute the current through the LED by dividing the voltage output by

the value of the resistor used. The voltages are in the milli-volts and

may fluctuate, so just use the average.

Range of V output with covered LED: __________ mV Current:

____________

Range of V output with uncovered LED: _________ mV Current:

____________

1. The circuit you designed has the basis for photodetection, with the

LED as a primitive detector. Which instruments find use for a

photo-detector?

2. Was the output steady? Noise is a major issue in signal

amplification. How come

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RC Filters

Objective

To introduce students to the different types of filters, specifically the RC

filter circuit.

RC Circuit

A capacitor can store an electric charge while a resistor dissipates the

flow of charges as heat. A fully charged capacitor, when connected across a

resistive element, will lose its charge as current flows across the resistor.

Connecting a voltage source across a series R-C circuit will cause a charging

current to flow. This current changes with time as the voltages across the

resistor and capacitor changes.

By changing the source to a sine source, the frequency dependent

voltage and current relationship in a capacitor can be exploited. The capacitor

has a frequency-dependent resistance referred to as capacitive reactance.

By combining resistors and capacitors in RC circuits, a frequency-dependent

voltage divider circuit is realized. Thus is created a circuit in which the input

and output relationships are frequency-dependent. These circuits form the

basis of filters.

Filters

Fundamentally, all periodic fluctuations can be by a reduced to

combination of sine waves of different frequencies. Electrical signals are no

exception, and thus have their signature frequencies. In most cases, the

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frequency of the desired signal is known. Stray signals of different frequencies,

or noise, interfere with the transmission of signals. Most of the time, these

stray signals are unavoidably combined with the desired signal. However,

there are ways to remove the noise from signal transmissions.

Filters are used to weed out the unwanted signal frequencies. There are

four basic types of filters. A low-pass filter only lets lower frequencies pass

through. A high-pass filter lets higher frequencies pass through. A band-select

filter only lets a certain range of frequencies to pass through. A band-reject

filter lets all frequencies pass through except for a certain range of

frequencies.

In this lab, a simple RC filters characteristics are demonstrated.

Exercise

Filter Circuit

Construct the filter circuit shown below using CircuitMaker. The devices

and elements to be used can be found under .General in the Major

Device Class.

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Figure 1 RC filter circuit

Access the Device Selection window (Figure 2) by clickingDevices>Browse

Figure 2 Device Selection window with listed devices

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Under Major Device Class, select and place the following circuit

components in your circuit setup

Circuit

Component

Directory

SignalGenerator

.General>Instruments>SignalGenerator

Multimeter .General>Instruments>Multimeter

Resistor .General>Resistors>Resistor

Capacitor .General>Capacitors>Capacitor

Ground .General>Sources>Ground

Set parameters of the devices and elements in the experiment bydouble-clicking on devices and making the following changes to

the device parameters:

CircuitComponent

New Parameter

Signal Generator Peak amplitude =1.41 VFrequency = 1.000kHz

Multimeters Measure AC RMSResistor Resistance = 10k

ohms

Capacitor Capacitance = 0.1 uF

Figure 3 (Right)

Editing parameters of the

signal generator

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Click on the Running Man icon to run the analysis. Theoscilloscope window should appear and the cursor should becomea probe.

Select the voltage input and output nodes by holding the SHIFT key

and selecting the areas highlighted in Figure 4. If done correctly,

then waves similar to those in Figure 5 will appear on the

oscilloscope window.

Figure 3 Select the highlighted areas to measure voltage input and output

using the probe tool.

Figure 5 Waves generated in the oscilloscope window. Plotmarkers measure the phase shift at the amplitude of eachwave

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Measure the phase shift between output and input by dragging plot

markers a and b to the amplitudes of each wave (as shown in

Figure 4). Measure the amplitudes by dragging plot markers c and

d along the right edge of the oscilloscope. List the measurements

in Data Table 1.

To stop the simulation, click on the stop icon . Once the analysis

has stopped, adjust the signal generator frequency to 100 Hz and

measure the phase shifts and amplitudes.

Repeat this procedure for 10 Hz, 100 Hz, 160 Hz, 1kHz and 10 kHzfrequencies. Record the data in Data Table 1.

NOTE:

For low-frequency setups (i.e. 100 Hz and below), open the

Analyses Setup window by clicking Simulation>Analyses Setup.

Click on the Transient/Fourier button. Change the Step Time to

10.00 uS, Max Step to 10.00 uS and Stop Time to 100.00 mS.

Confirm the changes.

For frequencies above 1 KHz, adjust the Step Time to 1.00 uS and

Max Step to 1.00 uS.

Bode Plot

Disassemble the filter circuit. Construct the new circuit as shown in

Figure 6 below.

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Figure 7 New circuit setup with capacitor as test point

Select voltage across the capacitor with the probe tool

To set up and run an AC analysis, connect a signal generator to thecircuit. Double-click on the signal generator to open the window inFigure 8a. Click on Wave to access the window in Figure 8b. CheckSource underAC Analysis.

Figure 8 a) Left. Edit Sine Wave window. b) Edit signal generatorwindow.

Go to Simulation>Analyses Setup and disable all options exceptAC(as in Figure 9)

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Figure 9 Uncheck all options in Analyses Setup window except for AC

In the same window, click on AC and check Enabled. Change the Start

Frequency to 10. 00 Hz, the Stop Frequency to 10.00 kHz, the

number of test points to 10 and then select Decade Sweep (as in

Figure 10)

Figure 10 AC Analysis Setup window

Run the simulation. Open the Graph Settings window (Figure 11) by

clicking on the Graph Settings icon . Use this window to make

adjustments to the oscilloscope graph settings. Adjust and view

the following graph settings in the oscillograph. Observe how the

graphs are able to quickly perform and plot the phase shift

measurements in Part A.

X-grid Functio

n

Y-Grid Functio

n

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Magnitud

e

Log X Magnitude Linear Y

Magnitud

e

Log X Magnitude Log Y

Magnitude

Log X Phase indegrees

Linear Y

Figure 11 Graph Settings window. Parameters for the x and y-axes

as well as the function can be changed in this window

Swap the positions of the resistor and capacitor. Again obtain the

amplitudes and phase shifts of the signals at 10 Hz, 100 Hz, 160

Hz, 1kHz and 10kHz. Also obtain the Bode plots as in the previous

number.

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Source:

(1) Boylestad, R.L.; Nashelsky, L. Electronic Devices and Circuit Theory, 8th Ed., Prentice

Hall, 2002

(2) Modifications from Electronics Class 2009.

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RC Filters

Group Name: _________________

Name: ______________________________

DATA

Note: Report all data (voltage, frequency and phase shift) up to 4

significant figures

Table 1

Frequenc

y

Vin (V) Vout (V) Vout/ Vin * t [a-b]

(s)

Phase

Shift ()10 Hz100 Hz160 Hz

1 kHz10 kHz

*time delay between input and output waveform

1. Compute the phase shift as follows:

(degrees) = t x f x 360

where f = frequency

2. Using the data above, plot the frequency response in the graphs provided.

What type of filter is this? _____________________

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3. Using the data above, find the frequency where Vout = 0.707Vin.

Frequency = ___________ Hz

Compare this with fc = 1/ (2RC) where R= resistance, C= capacitance.

4. What is the phase shift at this frequency?

Phase shift = ___________ degrees (indicate sign)

5. Encircle your answer: In this circuit, Vout lags/leads Vin

Table 2 (after swapping R and C)

Frequenc

y (f)

Vin (V) Vout (V) Vout/ Vin t (a-b)

(s)

Phase

Shift ()10 Hz100 Hz160 Hz1 kHz10 kHz

6. Compute the phase shift as follows:

(degrees) = t x f x 360


What type of filter is this? _____________________

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8. Using the data above, find the frequency where Vout = 0.707Vin.

Frequency = ___________ Hz

Compare this with fc = 1/ (2RC)

9. What is the phase shift at this frequency?

Phase shift = ___________ degrees (indicate sign)

10. Encircle your answer: In this circuit, Vout lags/leads Vin

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Digital Electronics

Objectives

The experiment aims to:

to familiarize the students with the use of TTL ICs and the truth table.

to be able to construct circuits using the AND, OR, NAND and NOR TTL

ICs

to solve logic problems using the different logic gate combinations.

Material

7408

7432

7402

7400

Digital Multimeter (DMM) Power Supply with 5 V regulator

Wires

Theories and Concepts:

Logical Operations

Aside from arithmetic operations and binary numbers, the basis of

digital electronics includes logical operations. The most common logic

operations are NOT, OR and AND operations. Each logic operations are

used differently from each and used in different logic problems.

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COMMON LOGIC OPERATIONS

NOT operation

This logic operation produces an output that is the

compliment of the operand or the input. For example, if your input

is equal to 1, then using the NOT operation would result to an

output equal to 0. In some notations, stating this would be: NOT

1=0. The symbol for NOT is - or by putting a bar above the

operand.

Example:

-(10010) = 01101

100101 = 011010

OR operation

This logic operation produces an output equal to 1 if there is

at least one operand or input that is equal to 1. For example,given the inputs 1010, using the OR operation would result to an

output equal to 1 since there is at least one operand equal to 1. In

some notations, we could state this example as 1 OR 0 OR 1 OR 0

= 1. The symbol for OR is +.

Example:

1 + 0 = 1, 0 + 0 = 0

10001 + 01010 = 11011

AND operation

This logic operation produces an output that is equal to 1 if

all the inputs are equal to 1. If at least one of the operand is equal

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to 0, the output will be 0. For example, given the inputs 1011,

using the AND operation would result to an output equal to 0 since

there is an input equal to 0 in the given (can also be stated as: 1

AND 0 AND 1 AND 1 = 0). Given the inputs 1111, using the same

operation would give an output reading equal to 1 since all inputs

in the given is equal to 1 (can also be stated as: 1 AND 1 AND 1

AND 1 = 1). The symbol for AND is &.

Example:

11111 & 10001 = 10001

00000 & 11111 = 00000

Other operations:

The NOR and NAND operations are basically the OR and

AND operations with their inputs negated (NOT-OR AND NOT-

AND).

Example:

10100 NOR 11010 = 00001 10111 NAND00101 = 11010

00001 NOR 10001 = 01110 11100 NAND

10101 = 01011

Logic Gates

The logic gates that are used today in integrated chips (ICs) use

transistors to simulate logical operations, thus they are called transistor-

transistor logic (TTL) ICs. The ICs that will be used in the experiment are

quad 2-input logic gates. The quad term refers to the number of logic

gates in the IC and the 2-input means that each logic gates requires 2

inputs to operate. In other words, there are four logical operating units

in each IC taking in two separate inputs each.

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Logic gate operations can be used in combination with each other in

order to produce a desired set of output values as written in your truth

table. TTL ICs can be used with each other to make circuits with the

desired output value.

Examples of Possible Ways of Combining Logic Gate Operations are

shown in Figure 2.

Figure 2. Possible Ways of Combining Logic Gates

Truth Tables

The truth table is an easy way of determining how a logical

operation proceeds given the different possibilities of inputs. In this

table, all possible input combinations are listed. Using a specific logicoperation, the output is also tabulated at the last column of the table.

Example: Using the AND logic gate and a 2-input system:

Figure 3: AND Truth Table

A B Y(output)

0 0 00 1 0

1 0 01 1 1

Exercise

A. Basic Logic Gates

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Each student will be provided with two of the following ICs: 7400, 7402,

7408, and 7432. These are the AND, OR, NAND and NOR quad gates. The pin

assignments are shown below:

Connect the Vcc to +5 V

and the ground pin to ground.

Five volts applied to an input of the IC is considered a signal high (1).

This voltage requirement is for TTL but for other low-powered ICs like CMOS,

the voltage requirements for a signal high may be lower. Connecting the input

to ground is considered a signal low (0). Using the DMM connected to the

output and to the ground, construct the truth table for each of your ICs as

shown below:

7400 7402

7408 7432

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Exhaust all possible combinations of inputs and check the outputs of

each. Any voltage read from the output of the IC is considered a signal high. A

0-V output is a signal low.

AND GateA B Y0 00 11 01 1

ORA B Y

0 00 11 01 1

NANDA B Y0 00 11 01 1

NORA B Y0 00 11 01 1

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B. The XOR operation

Another important logical operation is the exclusive OR or

XOR (F = x y). This is important in applications where only a

single high input generates an output high. The XOR truth table is

shown below:

Table 1. XOR Truth Table

x y F0 0 00 1 1

1 0 11 1 0

Using the two ICs you have, construct an XOR circuit. Draw

the schematic diagram of the circuit; draw the pertinent logic

gates and show how they are connected.

Hint: If you need to negate an input, you may use the NAND or

NOR gates. Any signal applied to both inputs of one of those gates

will generate the complement in the output.

C. Application

A certain instrument has three sensors for pressure,

temperature, and humidity. Abnormal conditions (high

temperature, low pressure, high humidity, etc.) cause the sensor

to generate a signal high. The instrument is designed to continue

operating even if abnormal pressure or humidity is detected, but

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not both at the same time. The instrument is not allowed to

operate at abnormal temperatures.

Construct a truth table for the sensing mechanism of this

instrument. Using the ICs provided, construct such a mechanism.

You may ask for additional ICs from your instructor.

Since this is a 3 input instrument, there will be 8 possible inputcombinations (23=8).

Truth Table for the InstrumentT P H Y0 0 0

0 0 10 1 00 1 11 0 01 0 11 1 01 1 1

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Source:

(1) Mano, M.M. Digital Design, 2nd Ed., Pearson Education, Asia Pte.

Ltd., 2001.

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Digital Electronics

Group Name: _________________

Name: _________________________________

A. Identify the ICs given to you:

Ex. 343 Dual operational amplifier

B. Draw the circuit diagram of the XOR gate you designed.

C. Draw the truth table of the circuit and the schematic diagram.

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RC Filters

Objective

To introduce students to the different types of filters, specifically the RC filter

circuit.

RC Circuit

A capacitor can store an electric charge while a resistor dissipates the flow of

charges as heat. A fully charged capacitor, when connected across a resistive element, will

lose its charge as current flows across the resistor. Connecting a voltage source across a

series R-C circuit will cause a charging current to flow. This current changes with time as

the voltages across the resistor and capacitor changes.

By changing the source to a sine source, the frequency dependent voltage and

current relationship in a capacitor can be exploited. The capacitor has a frequency-

dependent resistance referred to as capacitive reactance. By combining resistors and

capacitors in RC circuits, a frequency-dependent voltage divider circuit is realized. Thus

is created a circuit in which the input and output relationships are frequency-dependent.

These circuits form the basis of filters.

Filters

Fundamentally, all periodic fluctuations can be by a reduced to combination of sine

waves of different frequencies. Electrical signals are no exception, and thus have their

signature frequencies. In most cases, the frequency of the desired signal is known. Stray

signals of different frequencies, or noise, interfere with the transmission of signals. Most of

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the time, these stray signals are unavoidably combined with the desired signal. However,

there are ways to remove the noise from signal transmissions.

Filters are used to weed out the unwanted signal frequencies. There are four basic

types of filters. A low-pass filter only lets lower frequencies pass through. A high-pass

filter lets higher frequencies pass through. A band-select filter only lets a certain range of

frequencies to pass through. A band-reject filter lets all frequencies pass through except for

a certain range of frequencies.

In this lab, a simple RC filters characteristics are demonstrated.

Exercise

A. Construct the filter circuit shown below using CircuitMaker (Figure 1). The devices

used are all under the .General Major Device Class:

Signal Generator (.GeneralInstrumentsSignal Gen)

Multimeter (.GeneralInstrumentsMultimeter)

Note: Set to MeasureAC RMS

Resistor (.GeneralResistorResistor)

Capacitor (.GeneralCapacitorsCapacitor)

Ground (.GeneralSourcesGround)

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AC V

999.8mV

AC V

163.2mV

C10.1uF

1kHz

V1-1.41/1.41V R1

10k

Figure 1. Filter circuit

Double-click on the signal generator and set the Peak Amplitude to 1.414 V and the

Frequency 1.000 kHz. Click the running man icon to run the analysis. When

computation is finished the oscilloscope window appears. The cursor now becomes the

oscilloscope probe. Shift-click to select the voltage input and voltage output nodes as

indicated by the arrows on the following figure. If you do not press SHIFT while selecting,

only the last selection will be plotted.

Figure 2. Multimeter Device

V out

V in

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Figure 3. Oscilloscope window

On the oscilloscope window, use the plot cursors to select specific points on the

waves (Figure 3). The RMS amplitudes of the two test points are also given by the

multimeters. Also, measure the phase shift between output and input. Adjust markers a

and b (horizontally), and also c and d (vertically) to measure amplitudes and times,

respectively. Write these data down.

Click STOP to end simulation. Adjust the function generator frequency to 100 Hz.

Again, turn the analysis on then measure the amplitudes and phase shifts of the two signals

as before.

Do the procedure for 10 Hz, 100 Hz, 160 Hz, 1kHz and 10 kHz frequencies. You

can change the function generator frequency by double-clicking function generator and

setting the variables as follows (Figure 4):

Click and drag marker

Marker measurements are displayed here

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Figure 4. Editing function generator variables.

You must also setup analysis parameters as follows (Figure 5):

Figure 5. Set-up analysis parameters.

For Low frequency (100Hz and below), use the following set up (Figure 6):

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Figure 6. Low-frequency set-up

The following settings might be better for f 1 KHz (Figure 7):

Figure 7. Settings for frequency more than 1 kHz

Bode Plot

Edit the circuit to remove the multimeters. Select the voltage across the capacitor

as a test point to display on the scope as shown below (Figure 8).

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C1

0.1uF

1kHz

V1-1.41/1.41V R1

10kV(3)

Figure 8. Configuration for capacitor as test point.

To set up and run an AC Analysis:

1. Connect at least one Signal Generator to the circuit and enable it as an AC Analysis

source. Do this by double-clicking the Signal Generator, clicking Wave, and setting up the

AC Analysis Source options. Disable the other options (e.g. DC, Transient/Fourier,

Multimeter)

2. Choose Simulation > Analyses Setup > AC.

3. Enter the AC Analysis settings (see the following figure), select the Enabled check box,

and then choose OK.

Sweep Option: What it Means

Linear: Total number of Test Points in the sweep.

Decade: Number of Test Points per decade in the sweep.

Octave : Number of Test Points per octave in the sweep.

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Analysis setup:

Figure 9. Analysis set-up.

AC Analysis Setup:

Figure 10. AC analysis set-up

5. Run the simulation.

Graph settings (click on the icon to edit graph settings). You should view:

Magnitude (Linear Y Grid, Log X Grid and also Log X, Log Y)

Phase in degrees (Linear Y Grid, Log X Grid)

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Figure 11. Graph settings.

Note how the AC Analysis rapidly confirms the step-by-step determinations that you did

earlier.

B. Swap the positions of the resistor and capacitor. Again, get the amplitudes and

phase shifts of the signals at 10 Hz, 100 Hz, 160 Hz, 1kHz and 10 kHz. Also obtain the

Bode plot as above.

Source:

(1) Boylestad, R.L.; Nashelsky, L. Electronic Devices and Circuit Theory, 8th Ed.,

Prentice Hall, 2002.

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RC Filters

Group Name: _________________

Name: ______________________________

A.

Frequency Vin Vout Vout / Vin Phase shift

10 Hz

100 Hz

160 Hz

1 kHz

10 kHz


2. What type of filter is this? ____________________

3. In the Bode plot window, use the markers to find the frequency where Vout = 0.707

Vin. Frequency = _______Hz. Compare this with fc =1/(2RC).

4. In the Bode plot of phase versus frequency, what is the phase shift at this frequency?

Phase shift = ______________ degrees (indicate sign)*.

5. Encircle your answer: In this circuit, Vout lags/leads Vin .

B. (after swapping R and C)

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Frequency Vin Vout Vout / Vin Phase shift

10 Hz

100 Hz

160 Hz

1 kHz

10 kHz


7. What type of filter is this? ____________________

8. In the Bode plot window, use the markers to find the frequency where Vout = 0.707

Vin. Frequency = _______Hz. Compare this with fc =1/(2RC).

9. In the Bode plot of phase versus frequency, what is the phase shift at this frequency?

Phase shift = ______________ degrees (indicate sign)*.

10. Encircle your answer: In this circuit, Vout lags/leads Vin .

*Compute phase shift as follows: (degrees) = t * f / 360

Where:

t = time delay between input and output waveform in seconds

f = frequency in Hz

A. Graphs of frequency response:

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B. Graphs of frequency response:

Frequency response of RC filter: Magnitude

Type: _____ - pass

00.10.20.30.40.50.60.70.80.9

1

10 100 1000 10000

Frequency (Hz)

Magnitude(Vout/

Frequency response of RC filter: Phase

Type: _____ - pass

-90

-45

0

45

90

10 100 1000 10000

Frequency (Hz)

Phase

(degre

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B. Graphs of frequency response.

Frequency response of RC filter: Magnitude

Type: _____ - pass

0

0.10.20.30.40.50.60.70.80.9

1

10 100 1000 10000

Frequency (Hz)

Magnitude(Vout/

Frequency response of RC filter: Phase

Type: _____ - pass

-90

-45

0

45

90

10 100 1000 10000

Frequency (Hz)

Phase

(degre

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Microcontroller I: ADC

Objectives

(1) To introduce students to data acquisition using a microcontroller.

(2) To familiarize students on microcontroller peripherals, particularly the analog-to-

digital converter (ADC).

The Zilog Encore!TM Miniboard

Encore PLCC Mini Board (Figure 1) is a module that utilizes the on-chip

peripherals of the Z8F6401 Flash Microcontroller, like the eight-channel Analog-to-Digital

Converter (ADC) and the Universal Asynchronous Receiver/Transmitter. The board has a

64-K flash memory and is powered using a 9VDC adapter. This module uses pin headers to

access the input/output pins of Z8F6401.

Figure 1. PLCC Miniboard

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The ZDS II Encore Software

The Zilog Development Studio II has an integrated development environment and

has a built-in C compiler, assembler, linker and project manager. A debugger allows

single-stepping, viewing of variables, register files, code/data memory, ports and timers.

The ZDS II connects to the microcontroller (uC) via serial port communications. When

programming in the ZDS II environment, the user should know these ZDS II basics:

A. Creating a New Project

To start a new project (Figure 2) in ZDS II environment, click File and choose,

New Project.

Figure 2. New Project Window

Select target, CPU and Project Type as shown above. After that, select the location

for the new folder and write the folder name for the new project. Finally, type the filename

for the new project (Figure 3).

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Figure 3. New folder for new project

In the New Project window, click continue and wait for the Configure New

Project window to appear (Figure 4). Make sure that C Runtime Library and Floating

Point library are selected. After that, select startup module, dynamic frames and large

memory model.

Figure 4. Configure New Project Dialog Box

Click next, then review target memory configuration. Make sure that the settings are the

same as that shown in Figure 5, then click Finish.

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Figure 5. Configuring New Project

To check target system settings, click on Project then Settings and select the

Debugger tab (Figure 6). Make sure that the Z8 Encore! OCD Driver is selected. Else,

click on Configure Driver and change to the appropriate setting. Click on the C tab

and make sure the appropriate settings are made in the General category, particularly

disable optimizations. (Figure 7)

Figure 6. Debugger Tab in Project Setting Dialog Box.

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Figure 7. C Tab in Project Setting Dialog Box.

In the Preprocessor category, add __Z8F640 in the preprocessor definitions (Figure 8).

Figure 8. Preprocessor Definitions.

B. Creating a New Source Code File

To create a source code file, click File then select New File (Figure 9). After

coding in C, click File then select Save As and write the filename with a .c

extension. Make sure that the file is saved in the folder for the project. To create source

code file, choose Project Files then right click. Select Add Files to Project. Choose

the .c file of choice (Figure 10).

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Figure 9. New Source Code File

Figure 10. Add Files to Project

Figure 11 shows some of the shortcuts worth mentioning. Compile means

converting source code into op-codes / object code / machine code. Link, on the other hand

pertains to combining all these object codes. Build is tantamount to compiling followed by

linking. Syntax errors appear in the output window (Figure 12). Double-clicking on an

error message takes the programmer to the offending line.

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Figure 11. Shortcut Icons

Figure 12. Output Window

Exercise

In this exercise, you will input varying voltage into one of the analog inputs of the

Miniboard and obtain the digital output using Hyperterminal serial communications

program. This output is compared to the voltage input measured by a multimeter.

In interfacing the Encore PLCC Mini Board to a PC, RS-232 or serial

communication is used. A program (adc.c) written in C can be downloaded into the 64-K

flash memory via a serial cable from COM 1 (9-pin) to Debugger UART. To output data

generated by the Z8F6401, it is necessary to connect the Console UART to COM 2 (9 or

25-pin). In case COM 2 is 25-pin, a 9-to-25 serial cable should be employed.

IMPORTANT NOTE: Ask the instructor to interface the Miniboard to the PC

and to provide the text file of adc.c. Copy-paste this code to the New Source Code File

window.

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Sources:

(1) De Vera, I.M.S. Laboratory Data Acquisition System Based on the Z8 Encore!TM

Microcontroller. 2006.

(2) De Vera, I.M.S.; Chainani, E.T. Low Cost Laboratory Data Acquisition System

Based on the Z8 Encore!TM Microcontroller for pH Measurement. Kimika, 22, 2, 97-

83, 2006.

(3) Sison, L.G.; Burgos, O.T. Microcontroller for Data Acquisition and Motor

Control. 2005.

Microcontroller I: ADC

Group Name: _________________

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Name: _________________________________

A. Draw your potentiometer-potential divider circuit design here.

B. Comparison of Analog input and ADC output

Nominal Analog

Input (V)

Actual Analog Input

(V)

ADC Output from

Hyperterminal (V)

% Difference

0.025

0.050

0.075

0.100

0.200

0.300

0.400

0.5001.00

1.25

1.50

1.75

2.00

2.25

2.50

2.75

3.00

1. How is analog-to-digital conversion performed? Focus your research on the

algorithm used by sigma-delta ADCs (the ADC used by the Z8F6401

microcontroller).

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2. Plot decimal equivalent of the ADC output vs. voltage input for two voltage ranges:

0.025 to 0.500-V and 1.00 to 3.00-V. Take note of the linearity coefficient and the

slope of the plots (submit worksheet and graph separately). What can you say

about the sensitivity of the ADC as the analog input increment becomes smaller?

Comment on the accuracy of ADC conversion as the input approaches zero (i.e.

100 mV down to 25 mV).

3. Determine the step-size of the ADC (voltage change needed for ADC value to

change by one unit).

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Microcontroller II: Sensor

Objective

To create a Z8 Encore!TM based pH measurement system using a glass electrode.

pH Measurements using a Glass Electrode

The glass electrode is undisputedly the most important indicator electrode for

hydrogen ion. It is convenient to use and subject to few of the interferences that affect

other pH-sensing electrodes. One of the most important developments in chemical

instrumentation over the past three decades has been the advent of compact, inexpensive,

versatile integrated-circuit amplifiers (op-amps). These devices allow us to make potential

measurements on high-resistance cells, such as those that contain a glass electrode, without

drawing appreciable current. Even a small current (10-7 to 10-10 A) in a glass electrode

produces a large error in the measured voltage due to loading and electrode polarization.

Framework

This experiment can be more understood by looking at the block diagram in Figure

1.

Host PC or

PDAZ8F6401 uC

ADC

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Design an amplifier circuit using op-amp A in LF353N (see Figure 2, Expt. 6),

which can amplify the incoming analog signal from the glass electrode by a factor of 8.3.

Put a 0.1 uF non-polarized capacitor between the output and the inverting input of the

amplifier.

Using a BNC connector, connect the glass electrode to the non-inverting input of

this op-amp. Make the necessary tests if the amplifier circuit is working.

A.3 Level Shifter

Figure 2 shows the level shifter circuit. Implement this circuit on your bread board.

If one measures the amplified voltage (output of A.2), negative values above pH 7

will be obtained. This signal is not fit as an ADC input. (Why?). Thus, the amplified

analog signal needs to be level-shifted to positive voltage values. A voltage-follower is

implemented via op-amp B in LF353N. Consequently, Vshift is equal to VCC. An external

voltage reference set to 3.3 V (designated as VCC in Fig. 2 , see also Fig. 1, Expt. 9) is

employed. Note of the label amplifier output in figure 2. This is where you connect the

amplifier output. VDD in the same figure is pin 21 of the Miniboard.

Inspect Figure 2 thoroughly. Justify that the signal is indeed level-shifted to

positive values and that the following equation can be derived from your amplifier circuit

design and the level shifter:

2

]30.3)27.8*[( +=

VinVout Equation 1

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Moreover, test your circuit if the output abides Equation 1. The level-shifted signal (Vout)

will now serve as the input to ANA0 of the ADC.

Figure 2. Level Shifter

B. Interfacing the Miniboard and Loading the software

As before, ask the instructor to interface the PLCC miniboard to the PC. Open the

file pHmeter.c using ZDS II (refer to Experiment 9 for procedures). Click the following

icons in succession: CompileBuildConnect to TargetDownloadGo. Make sure

that Hyperterminal is on-line.

C. Making pH measurements

Vcc (3.30 V)

Vout

Vshift

VDD

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The groups will share the standard buffer solutions for the calibration phase. Each

group will receive three unknowns. Your task is to get the pH of the unknown solutions

using your groups pH meter and compare this to the pH measurement obtained by using

a commercial pH meter (i.e. Sartorius).

Sources:

(1) De Vera, I.M.S. Laboratory Data Acquisition System Based on the Z8 Encore!

TM Microcontroller. 2006.

(2) De Vera, I.M.S.; Chainani, E.T. Low Cost Laboratory Data Acquisition System

Based on the Z8 Encore!TM Microcontroller for pH Measurement. Kimika, 22, 2,

97-83, 2006.

(3) Sison, L.G.; Burgos, O.T. Microcontroller for Data Acquisition and Motor

Control. 2005.

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Microcontroller II: Sensor

Group Name: _________________

Name: _________________________________

Calibration Phase

pH Standard Buffer Decimal Value of ADC

Output

Voltage Equivalent

4.00

7.00

10.00

pH Measurements

Unknown pH Miniboard pH Sartorius % difference

1

2

3

1. Draw your amplifier circuit design here.

2. (a) The 0.1 uF capacitor in the amplifier circuit acts as what type of filter?

Calculate the cut-off frequency.

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(b) The 10 uF capacitor parallel to the output of the level shifter is similar to the

filter in (a). Calculate its cut-off frequency.

3. Prove Equation 1.

4. Plot the pH calibration curve (decimal equivalent of ADC output vs. voltage in V)

in Excel or simply determine the linearity coefficient using your calculator.

Which is better, a three-point or a two-point calibration? Why?

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5. Account for the difference between the pH measurements made using the

microcontroller-based pH meter and the commercial pH meter (Sartorius).

Evaluate the accuracy and precision of measurements using the microcontroller-

based pH meter.

6. What are the factors that may lead to errors in pH measurements?

Appendix A: Soldering

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Soldering is accomplished by quickly heating the metal parts to be joined, and then

applying aflux and asolder to the mating surfaces. The finished solder joint metallurgically

bonds the parts forming an excellent electrical connection between wires and a strong

mechanical joint between the metal parts. Heat is supplied with a soldering iron or other

means. The flux is a chemical cleaner which prepares the hot surfaces for the molten

solder. The solder is a low melting point alloy of non-ferrous metals.

Soldering gun or iron

A soldering iron is an electric hand tool that joins two pieces of metals by fusing

their surfaces together using a metal alloy known as solder. Usually, for electronics, the

solder used is an alloy composed primarily of lead. A soldering iron will

melt the lead by applying constant heat to it. This melted lead, once it dries,

joins the two metal surfaces together.

A soldering gun operates with the same principle as a soldering iron,

but pressing its trigger can increase its heat.

Be careful in using a soldering tool, since it operates at high temperatures. Do not

play around with it. Also, do not inhale the smoke coming from soldering action, as it

contains irritants to mucous membranes.

Soldering lead

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Solder is a metal or metallic alloy used, when melted, to join

metallic surfaces together. The most common alloy is some

combination of tin and lead. Certain tin-lead alloys have a lower

melting point than the parent metals by themselves. The most common alloys used for

electronics work are 60/40 and 63/37. The chart below shows the differences in melting

points of some common solder alloys.

Tin/Lead Melting Point

40/60 460 degrees F (230 degrees C)

50/50 418 degrees F (214 degrees C)60/40 374 degrees F (190 degrees C)



The eutecticum is the point where the melting point and solid point is the same and the

melting point is lower then the melting point of the individual metals used in the alloy. The

eutectic point in tin/lead alloy is 61.9% tin and 38.1% lead (if metals are 100% pure).

60/40 solder is commercially available and is recommended for solder work.

With non-eutectic alloys a paste-phase develops in the zone between the liquid and solid

line. In theory this could result in soldering failures if the solder joint in this paste-phase

undergoes mechanical stress or gets serious vibration. Small tolerances from the eutectic

point have little influence in the soldering process because of fast cooling.

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Most soldering jobs can be done with flux-cored solder (solder wire with the

flux in the center) when the surfaces to be joined are already clean or can be

cleaned of rust, dirt and grease. Flux can also be applied by other means (it is

also sold separately in tin cans). Flux only cleans oxides off the surfaces to be soldered. It

does not remove dirt, soot, oils, silicone, etc.

Base Material

The base material in a solder connection consists of the component lead and the plated

circuit traces on the printed circuit board. The mass, composition, and cleanliness of the

base material all determine the ability of the solder to flow and adhere properly (wet) and

provide a reliable connection.

If the base material has surface contamination, this action prevents the solder from wetting

along the surface of the lead or board material. A surface finish usually protects component

leads. The surface finishes can vary from plated tin to a solder - dipped coating. Plating

does not provide the same protection that solder-coating does because of the porosity of the

plated finish, thus the component wire may develop oxides.

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The Correct Way to SolderSome Reasons for Unwettability

1. The component lead has developed an oxide. Normally this can be removed by the

flux, but a thick layer of oxidation requires removal by sandpaper or other

mechanical means.

2. The selected temperature is too high. The tin coating is burnt off rapidly and

oxidation occurs.

3. Oxidation may occur because of wrong or imperfect cleaning of the tip: when other

material is used for tip cleaning instead of the original damp Weller sponge. A

damp cellulose sponge is recommended; other sponges, rags or cloth will melt or

burn.

4. Use of impure solder or solder with flux interruptions in the flux core.

5. Insufficient tinning when working with high temperatures over 665 degrees F (350

degrees C) and after work interruptions of more than one hour.

6. A "dry" tip, i.e. the tip is allowed to sit without a thin coating of solder oxidation

occurs rapidly.

7. Use of fluxes that are highly corrosive and cause rapid oxidation of the tip (e.g.

water soluble flux).

8. Use of mild flux that does not remove normal oxides off the tip (e.g. no-clean flux).

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The Soldering Iron Tip

The soldering iron tip transfers thermal energy from the heater to the solder

connection. In most soldering iron tips, the base metal is copper or some copper alloy

because of its excellent thermal conductivity. A tip's conductivity determines how fast

thermal energy can be sent from the heater to the connection.

Both geometric shape and size (mass) of the soldering iron tip affect the tip's

performance. The tip's characteristics and the heating capability of the heater determines

the efficiency of the soldering system. The length and size of the tip determines heat flow

capability while the actual shape establishes how well heat is transferred from the tip to the

connection.

There are various plating processes used in making soldering iron tips. These

plating operations increase the life of the tip. The figure below illustrates the two types of

plating techniques used for soldering iron tips. One technique uses a nickel plate over the

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copper. Then, an iron electroplate goes over the nickel. The iron and the nickel create a

barrier between the copper base material and tin used in the solder alloy. The barrier

material prevents the copper and tin from mixing together. Nickel-chrome plating on the

rear of the tip prevents solder from adhering to the back portion of the tip (which could

cause difficulty in tip removal) and provides a controlled wetted area on the iron tip.

Another plating technique is similar but omits the nickel electroless plating, leaving the

iron to act as the barrier metal.

How to Care For Your Tip

Because of the electro-plating Weller tips should never be filed or ground. Weller

offers a large range of tips and there should be no need for individual shaping by the

operator.

Although Weller tips have a standard pre-tinning (solder coating) and are ready for

use, it is recommended that you pre-tin the tip with fresh solder when heating it up the first

time. Any oxide covering will then disappear. Tip life is prolonged when mildly activated

rosin fluxes are selected rather than water soluble or no-clean chemistries.

When soldering with temperatures over 665 degrees F (350 degrees C) and after

long work pauses (more than 1 hour) the tip should be cleaned and tinned often, otherwise

the solder on the tip could oxidize causing unwettability of the tip. To clean the tip use the

original synthetic wet sponges from Weller (no rags or cloths).

When doing rework, special care should be taken for good pre-tinning. Usually

there are only small amounts of solder used and the tip has to be cleaned often. The tin

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coating on the tip could disappear rapidly and the tip may become unwettable. To avoid

this the tip should be re-tinned frequently.

Additional Tip and Tiplet Care Techniques

Listed below are suggestions and preventative maintenance techniques to extend life and

wettability of tips and desoldering tiplets.

1. Keep working surfaces tinned, wipe only before using, and return immediately.

Care should be taken when using small diameter solder to assure that there is

enough tin coverage on the tip working surface.

2. If using highly activated rosin fluxes or acid type fluxes, tip life will be reduced.

Using iron plated tips will increase service life.

3. If tips become unwettable, alternate applying flux and wiping to clean the surface.

Smaller diameter solders may not contain enough flux to adequately clean the tips.

In this case, larger diameter solder or liquid fluxes may be needed for cleaning.

Periodically remove the tip from your tool and clean with a suitable cleaner for the

flux being used. The frequency of cleaning will depend on the frequency and type

of usage.

4. Filing tips will remove the protective plating and reduce tip life. If heavy cleaning

is required, use a Polishing Bar available from your distributor.

5. Do not remove excess solder from a heated tip before turning off the iron. The

excess solder will prevent oxidation of the wettable surface when the tip is

reheated.

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temperature when the most commonly used solders have a melting point under 400 degrees

F. Using a higher temperature stores heat in the tip, which speeds up the melting process.

The operator can then complete the solder connection without applying too much pressure

on the joint. This practice also allows a proper formation of an intermetallic layer of the

parts and solder. This is critical for reliable electrical and mechanical solder joints.

The Operator's Effect on the Process

The operator has a definite effect on the manual soldering process. The operator

controls the factors during soldering that determine how much of the soldering iron's heat

finally goes to the connection.

Besides the soldering iron configuration and the shape of the iron's tip, the operator

also affects the flow of heat from the tip to the connection. The operator can vary the iron's

position and the time on the connection, and pressure of the tool against the pad and lead of

the connection.

When the tip of the iron contacts the solder connection, the tip temperature

decreases as thermal energy transfers from the tip to the connection. The ability of the

soldering iron to maintain a consistent soldering temperature from connection to

connection depends on the iron's overall ability to transfer heat as well as the operator's

ability to repeat proper technique.

The Reliable Solder Connection

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Two connection elements must properly function for a solder joint to be reliable.

The solder within the connection must mechanically bond the component to the PCB. The

connection must also provide electrical continuity between the device and board. The

proper intermetallic layer assures both.

Mechanical

In surface mount and nonclinched through-hole technology, the solder provides the

mechanical strength within the connection. Important factors for mechanical strength

include the wetting action of the solder with the component and board materials, physical

shape and composition of the connection, and the materials' temperature within the

connection during the process. The connection temperature should not be too high, causing

embrittlement, or too low, resulting in poor wetting action.

Electrical

If a solder connection is mechanically intact, it is considered to be electrically

continuous. Electrical continuity is easily measured and quantified.

Testing Reliability

Two easily measured indicators in the soldering process that can determine the

reliability of the solder connection are the soldering iron's tip temperature and the solder's

wetting characteristics. The tip's temperature during the soldering process is an indicator of

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the amount of heat being transferred from the tip to the connection. The optimum rate of

heat transfer occurs if the soldering iron tip temperature remains constant during the

soldering process.

Another indicator for determining reliability is the solder's wetting action with the

lead and board materials. As operators transfer heat to the connection, this wetting

characteristic can be seen visually. If the molten solder quickly wicks up the sides of the

component on contact, the wetting characteristic is considered good. If the operator sees

the solder is flowing or spreading quickly through or along the surface of the printed circuit

assembly, the wetting is also characterized as good.

Right Amount of Solder

a) Minimum amount of solder

b) Optimal

c) Excessive solder

Solderability

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a) Bad solderability of terminal wire

b) Bad soldering of PCB

c) Bad soldering of terminal wire and PCB

Key Points to Remember

1. Always keep the tip coated with a thin layer of solder.

2. Use fluxes that are as mild as possible but still provide a strong solder joint.

3. Keep temperature as low as possible while maintaining enough temperature to

quickly solder a joint (2 to 3 seconds maximum for electronic soldering).

4. Match the tips

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