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Reading voltages on the Arduino UNO and Board of Education

We have just confirmed a 5-volt DC power source, which is available on the Arduino and Board of Education. This 5-volts power source is coming from the USB power source from the computer or the transformer you measured earlier, however, the 17-volts DC is first going through another special part which regulates the voltage down to 5-volts DC. This specialty part is called a lm7805 and is used to create very controlled and clean regulated voltage.


There is also a part called an LM7809 designed to take a higher voltage and regulate it to a clean 9-volts DC and a 78012 which is designed to take a higher DC voltage and regulate it to a clean 12-volts. DC.

It is easy to take a reading of the LM7805 voltage regulating chip but do this very carefully as if you accidentally short your multimeter probes together while you take voltage measurements you can damage the LM7805 voltage regulator.

This 5 volts regulated source is valuable, as many of the electronic parts we will be using will need an independent power source. Keep in mind that while you can use this power source for driving the Arduino or the Basic Stamp 2 it can also be used to drive other 5-volt DC electronic parts, however, you must not overburden the 7805 power part with too much demand for the voltage as there must always be enough for the microcontroller.

Look at the black socket on the left side of the White bread and to the left of the small silver switch. You will notice an open socket with white silk screen lettering around it starting with S out, and below this Sin, etc.

Board of Education without the Basic Stamp 2 installed.

This is where the Basic Stamp will be seated; but first, let us take some voltage measurements.

    Be very careful not to accidentally short two of the sockets together. Hold your hand against the table as you bring your probe tips into contact with the socket to steady your hands.

Put your black probe on the silver pin area of the socket closest to the VSS pin. Now put the red probe on the silver socket area neared the Vin pin. What is the voltage you are reading? ____________________________________

    Black probe on VSS and red probe on VIN


What happens when you reverse the probes? ________________________

    Black probe on VIN and red probe on VSS


  1. What does this tell you? _________________________________________
  2. Now take a voltage reading below. What is your reading?_______


Black probe on Sout and red probe on VIN