ME 445 – Lab 2: Safe digital I/0, Battery fundamentals
Objectives
Learn about using external voltage supplies, such as batteries. Learn about interfacing external devices,
such as a function generator to the Arduino.
1) Voltage regulator
Connect a 7805 voltage regulator as shown to the right. Use +15V from your breadboard
to provide VIN. Verify operation with your Digital Voltmeter (DVM).
This chip may be used to provide up to 1 A of +5V power for a variety of applications.
You may use power supplies or batteries to provide VIN.
7805
VIN
GND
+5V out
2) Protecting Arduino digital inputs
The PS2501 opto-isolator is shown below. It can carry 30 mA of collector-emitter current.
Connect a switch as shown below as an example of how to protect your Arduino from
higher input voltages. Write a brief Arduino program to verify operation.
Battery +9V
16 15 14 13 12 11 10 9
3K
Arduino +5V
5K
Arduino digital input
1
2 3
4 5 6 7 8
Battery GND
Arduino GND
3) Measure pulse length
Use an opto-isolator to interface a square wave from your function generator to an Arduino input pin.
Note that the function generator should never be connected directly to your Arduino because it produces
negative voltages. You may need a different resistor and you will not need the switch.
Use the Arduino pulseIn() function to measure frequency of the square wave. Verify operation.
4) Slotted optical switch
Connect a slotted optical switch as shown below. The slotted optical switch is internally the same as an
opto-isolator, except that you can manually block the light path. Verify operation using code from 2).
Arduino +5V
D
+
1K
Battery GND
+
E
Battery +9V
5K
Arduino digital input
Arduino GND
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ME 445 – Lab 2: Safe digital I/0, Battery fundamentals
5) Protecting Arduino digital outputs
Connect an LED to the isolated output as shown below as an example of how to protect your Arduino
from higher output voltages. Verify operation.
Arduino +5V
Battery +9V
1500
isolated test point
Arduino digital output
500
LED
Battery GND
6) Measuring battery voltage
We can’t use the Arduino to directly measure the voltage of the battery because the Arduino analog inputs
are limited to be between 0V and 5V.
Report: Design a circuit that will allow you to measure the battery voltage safely and include a circuit
diagram in your report. Verify that your code works by checking your measurements with a multimeter.
Hint: Lab 1 part 1 may be helpful.
Report
Include all of the items mentioned above and answer the following questions.
1) Your Arduino has a voltage regulator that reduces voltages on the pin labeled Vin to +5V. What is the
range of voltages you can supply to the Arduino on Vin?
2) Some voltage regulators can produce a higher output voltage than the input voltage. Find a link to a
regulator that performs this function.
Hint: Pololu.com has a nice selection of these regulators.
What are some of the drawbacks of this type of regulator?
3) In part 4, could you replace the battery with the 5V supply from your Arduino? Describe why or why
not.
Troubleshooting question: Pick the biggest problem you ran into while working on this lab and describe
the problem in your report. Also provide the steps you followed to solve the problem. Think about how
you could have determined what the problem was as quickly as possible and write about a method you
would use to diagnose similar problems in the future. If you didn’t run into any problems, you write about
what you think could have been a major issue.
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