Using the Board of Education Breadboard and Your Multimeter

ENGR 120

Work in teams of two!

Your Multimeter

leads

probes

pincer clips – good for workingwith Boe-Bot wiring

You will use the multimeter to understand and troubleshoot circuits, mostlymeasuring DC voltage, resistance and DC current.

turn knob to what youwould like to measure

(push these onto probes)

Measure VinVin will be the same as your power supply voltage. For the case below, 4 AAbatteries are used resulting in approximately 6 V (5.79 V to be more exact).

Vin = power supply voltage Vss = ground (negative side of battery)

Switch to DC Volts

Measure VddVdd will always be around 5V (it is 4.94 V here). A voltage regulator on the Board of Education reduces this voltage from Vin down to ~ 5V. The Boe-Bot operates on 5V DC.

Vdd ~ 5V Vss = ground (negative side of battery)

Select Resistors Find the 470 and the 10kresistors from your Boe-Bot kit.

Example: 470resistor:

4 = yellow7 = violetAdd 1 zero to 47 to make 470, so 1 = brown

Now, find the 10k resistor.

So, 470 = yellow, violet, brown

Diagram from the Parallax Robotics book

set multimeterto measure

R ~ 470

Check Resistance of Resistors

Connecting an LED

Electricity can only flow one way through an LED (or any diode).

LED = Light Emitting Diode

Diagram from the Parallax Robotics book

Building an LED Circuit

Vdd = 5V

LED

5V

+ -

470

These circuit diagramsare equivalent

these holes are “connected”

Vdd =

LED

holes in this direction are not connected

Diagram from the Parallax Robotics book

Replace the 470 Resistor with the 10k Resistor

What happens and Why??

ANSWER: The smaller resistor (470) provides less resistance to current thanthe larger resistor (10k). Since more current passes through the smallerresistor, more current also passes through the LED making it brighter.

What would happen if you forgot to put in a resistor? You would probably burn up your LED.

Connect the Resistor to Pin 12 (P12)

' {$STAMP BS2}' {$PBASIC 2.5}

DO HIGH 12 PAUSE 500 LOW 12 PAUSE 500LOOP

Enter and run the following PBASIC program:

Diagram from the Parallax Robotics book

Causes pin 12 to output a constant 5V (Vdd)

' {$STAMP BS2}' {$PBASIC 2.5}

DO HIGH 12 PAUSE 500 LOW 12 PAUSE 500LOOP

How the Program Worksin

finite

loop

Causes pin 12 to output a constant 0V (Vss)

HIGH = 5V and LOW = 0V (Always!!!!)

wait 500 ms

Wait 500 ms

Diagram from the Parallax Robotics book

Now Experiment on Your Own!

(1)Try changing the time to 1.5 seconds on and 1 second off

(2)Connect the resistor to pin 8 and change the program to match

(3)Blink out SOS in Morse code (dot-dot-dot-dash-dash-dash-dot-dot-dot)a. three short pulses (0.25 seconds each) followed by . . .b. three long pulses (0.75 second each) followed by . . .c. three short pulses (0.25 seconds each) followed by . . .d. a brief pause (1 second) e. repeat a through d using an infinite loop

Show your instructor when you have completed exercise (3).

' {$STAMP BS2}' {$PBASIC 2.5}

DO PULSOUT 12, 65000 PAUSE 2000LOOP

Enter and run the following PBASIC program:

Another Way to Make the LED Blink

Causes pin 12 to output a constant 5V for . . .

65000 x 2s = 130000 s = 0.13 sWait 2000 ms = 2 s

Diagram from the Parallax Robotics book

Find the PULSOUT Command Using PBASIC Help

Now, you change the program to make the LED blink on for a duration of 0.01 seconds and off for a duration of 0.1 seconds. Show your instructor.

The End