University of Ulster (Jordanstown) Technology & Design PGCE Electronics / Modelling in Livewire & PCB Wizard R.A. Moffatt. Automatic Switching:- Light

University of Ulster (Jordanstown) Technology & Design PGCE

Electronics / Modelling in Livewire & PCB Wizard

R.A. Moffatt.

Automatic Switching:-

Light / Temperature Sensing - Transistor Projects.

Live Wire


Aims:

To understand the concept of automatic switching / sensing in electronic circuits

To practice modelling basic electronic switching circuits using the Live Wire and PCB Wizard software

To construct (PCB’s) printed circuit boards

Automatic Switching: Transistor Project


Automatic Switching: Transistor Project

You will have an opportunity to:-

Design a temperature/light sensing circuit. To manufacture a printed circuit board.

Two of the circuits respond to a change in light levels and the other two respond to a change in temperature levels.


Practically every modern Intel Pentium processor

main board features a temperature sensor

developed at Delft University of Technology. The

sensor detects when the processor starts to

become too hot, and switches on a fan to cool it

down. As soon as the temperature drops to an

acceptable level, the fan is switched off. The

temperature sensor was developed by Dr. Anton

Bakker, who in April 2000…


Our Learning Intentions

• know how to use the Live Wire and PCB Wizard software

• how to design automatic control circuits• understand input sensors and transistor switching• an understanding of resistor colour codes using four

and five band resistors• circuit building skills developed by using the

soldering iron• practice at following detailed test procedures


We

Are

Learning

To

To understand the concept of a potential divider which provides automatic switching of electronic circuits

This is because .. We can learn how to design electronic circuits and systems using automatic switching for our project work

Remember to: • refer to the water analogy to help understand how the Potential divider works

ElectronicsWALT


WILF:

What

I am

Looking

For

• an understanding of the potential divider as

a sensor / automatic switch• the ability to sketch a circuit diagram of an

automatic temperature / light sensing

sensor circuit• to be able to model and test an automatic

switching circuit• to make a PCB and build a sensing circuit as

an example of a transistor-based control

system

Electronics


Preset – Variable Resistor

Light Dependant Resistor

Single-Pole-Single-Throw Switch

Componentsymbols

Potential Divider

9V

0V


X

Y

Y

X

B B

Water Pipe Analogy:

Diagram extracted from Making Things Work by Ken Shooter & John Saxton

The Potential Divider


Transistors are

semiconductor devices.

This means that they have

a resistance to the flow of

electrons – current.

However they become

conductors if a small

voltage is provided across

two of the legs – the base

and the emitter.

Collector (c)

Emitter (e)

Base (b)

Symbol for the n-p-n transistor

You can use the transistor as a high speed switch if a small voltage of

0.6 – 1.6V is applied to the base leg as shown below

The Transistor

Technology Education Centre 05.


The Transistor

Small Voltage in

Large Voltage

http://www.satcure-focus.com/tutor/page4.htm

PNP Transistor

B

C

E

symbol Saturated = ‘fully on’

B

C

E

0.6V

9V


Transistor Gain:

We know that a small current flowing at the base of the transistor will ‘turn on’ a large collector current. This is known as current Amplification.

The ratio I Iis a measure of the amplification which we call the transistors current gain. The symbol for the transistor current gain is

cb

hfe = IcIb

hfe

= 0.5 A0.00025 A

= 200

(0.00025A) (0.05A)


The Transistor

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/comp/active/BiPolar/page1.html

University of Ulster (Jordanstown) Technology & Design PGCE http://www.allaboutcircuits.com/vol_3/chpt_4/3.html


Bulb-’off’ when Dark

Transistor

LDR

V/Resistor

BULB ‘off’


Bulb-’on’ when Light

BULB ‘on’

Transistor

LDR

V/Resistor



LED-’off’ when Light shines on LDR

Transistor

LDR

VR

LED ‘off’


LED-’on’ when Dark


In the light the voltage between the

base and the emitter leg of the

transistor is 657mV or 0.65V. For this

transistor the voltage is not enough to

switch it on – therefore the bulb

remains off.

In the darkness the voltage between the

base and the emitter leg of the

transistor is 739mV or 0.739V. This

voltage is high enough to switch on the

transistor – therefore the bulb is

switched ‘on’.

Ex 1: Potential Divider / Dark Light ‘on’

a) Model the circuit using Live Wire as shown and test!a) Draw this circuit diagram in your folder and explain how it works?

‘OFF’

‘ON’


Ex 2: Dark Sensor: Circuit 4 from 112 Circuit Designs – M. Lynch

TIP 121 TIP 121

Light level low LED will be ‘on’

a) Model this circuit and test using Live Wire b) Draw this circuit diagram in your workbook and explain how it works? c) Convert this circuit to a PCB layout using PCB Wizard


Real World Normal

PCB: Printed Circuit Board

PCB Wizard


Printed Circuit Board


Circuit 5 A Light Sensing Transistor


M. Lynch

Play the AVI file to help understand how this circuit works?


Moisture.pdf

Double-Click the PDF icon to access the data sheet

House plants can suffer if owners do not give them the right amount of water. Houseplants can die if they do not receive enough water, and they can rot if over watered.


Moisture Tester

‘on’

moisture level




In a Darlington pair circuit, two transistors are wired together to provide better Switching.

Darlington Pair Driver


1) Make sketches of a 1K, 2k2, 680R and 470R resistor

include the colour code for each

2) Explain the function of a resistor in an electronic circuit?

3) Draw the two component symbols necessary and in the

correct order to make a potential divider that sounds a

buzzer when light shines on the LDR? One of these

component symbols have been drawn for you.

Electronics Year 9 Test


4) Explain how the circuit shown below works?

5) Suggest two uses for this type of circuit?

6) What is the trigger voltage for a BS 108 Transistor?

7) Sketch the symbol for a transistor and label the legs: -

emitter, collector, base


8) An electronic sensor is required for an elderly persons room that sounds an alarm when the room temperature drops to a certain level or gets ‘too cold’. Draw and complete the circuit diagram using symbols to show the type of sensor required?

9) Name each of the components used in your design?


10) Name each of the component shown below and explain briefly their function when used in an electronic circuit?


http://www.circuitspecialists.com/prod.itml/icOid/8181http://www.new-wave-concepts.com/br_files.html

Documents

University of Ulster (Jordanstown) Technology & Design PGCE Electronics / Modelling in Livewire & PCB Wizard R.A. Moffatt. Automatic Switching:- Light