Transcript Notes 3
Using the Board of Education
Breadboard and Your Multimeter
Work in teams of two!
ENGR 120
Your Multimeter
pincer clips – good for working
with Boe-Bot wiring
(push these onto probes)
probes
leads
turn knob to what you
would like to measure
You will use the multimeter to understand and troubleshoot circuits, mostly
measuring DC voltage, resistance and DC current.
Measure Vin
Vin will be the same as your power supply voltage. For the case below, 4 AA
batteries 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 Vdd
Vdd 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 470W and the 10kW resistors from your Boe-Bot kit.
Example: 470W resistor:
4 = yellow
7 = violet
Add 1 zero to 47 to make 470, so 1 = brown
So, 470 = yellow, violet, brown
Diagram from the Parallax Robotics book
Now, find the 10kW resistor.
Check Resistance of Resistors
R ~ 470W
set multimeter
to measure W
Connecting an LED
LED = Light Emitting Diode
Diagram from the Parallax Robotics book
Electricity can only flow one way through an LED (or any diode).
Building an LED Circuit
Vdd = 5V
+
-
LED
470W
LED
These circuit diagrams
are equivalent
these holes are “connected”
Vdd = 5V
holes in this direction are not connected
Diagram from the Parallax Robotics book
Replace the 470W Resistor
with the 10kW Resistor
What happens and Why??
ANSWER: The smaller resistor (470W) provides less resistance to current than
the larger resistor (10kW). Since more current passes through the smaller
resistor, 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)
Diagram from the Parallax Robotics book
Enter and run the following PBASIC program:
' {$STAMP BS2}
' {$PBASIC 2.5}
DO
HIGH 12
PAUSE 500
LOW 12
PAUSE 500
LOOP
How the Program Works
infinite loop
' {$STAMP BS2}
' {$PBASIC 2.5}
DO
HIGH 12
PAUSE 500
LOW 12
PAUSE 500
LOOP
Causes pin 12 to output a constant 5V (Vdd)
wait 500 ms
Causes pin 12 to output a constant 0V (Vss)
Wait 500 ms
Diagram from the
Parallax Robotics book
HIGH = 5V
and
LOW = 0V
(Always!!!!)
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).
Another Way to Make the LED Blink
Enter and run the following PBASIC program:
' {$STAMP BS2}
' {$PBASIC 2.5}
DO
PULSOUT 12, 65000
PAUSE 2000
LOOP
Diagram from the Parallax Robotics book
Causes pin 12 to output a constant 5V for . . .
Wait 2000 ms = 2 s
65000 x 2ms = 130000 ms = 0.13 s
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