Using the Board of Education Breadboard and Your Multimeter

1
Using the Board of Education Breadboard and Your
Multimeter
Work in teams of two!

• ENGR 120

2
Your Multimeter
pincer clips good for working with Boe-Bot
wiring
probes
(push these onto 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.
3
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
4
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)
5
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
Now, find the 10kW resistor.
Diagram from the Parallax Robotics book
6
Check Resistance of Resistors
R 470W
set multimeter to measure W
7
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).
8
Building an LED Circuit
Vdd
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
9
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.
10
Connect the Resistor to Pin 12 (P12)
Diagram from the Parallax Robotics book
Enter and run the following PBASIC program
11
How the Program Works
Causes pin 12 to output a constant 5V (Vdd)
wait 500 ms
infinite loop
Causes pin 12 to output a constant 0V (Vss)
Wait 500 ms
Diagram from the Parallax Robotics book
12
Now Experiment on Your Own!

• Try changing the time to 1.5 seconds on and 1
  second off
• Connect the resistor to pin 8 and change the
  program to match
• Blink out SOS in Morse code (dot-dot-dot-dash-dash
  -dash-dot-dot-dot)
• three short pulses (0.25 seconds each) followed
  by . . .
• three long pulses (0.75 second each) followed by
  . . .
• three short pulses (0.25 seconds each) followed
  by . . .
• a brief pause (1 second)
• repeat a through d using an infinite loop

13
Another Way to Make the LED Blink
Enter and run the following PBASIC program
Causes pin 12 to output a constant 5V for . . .
65000 x 2ms 130000 ms 0.13 s
Wait 2000 ms 2 s
Diagram from the Parallax Robotics book
14
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.
15
The End ?