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## Friday, September 5, 2008

### A very simple computer DC CIRCUITS

PARTS AND MATERIALS

• Three batteries, each one with a different voltage
• Three equal-value resistors, between 10 kΩ and 47 kΩ each

When selecting resistors, measure each one with an ohmmeter and choose three that are the closest in value to each other. Precision is very important for this experiment!

CROSS-REFERENCES

Lessons In Electric Circuits, Volume 1, chapter 10: "DC Network Analysis"

LEARNING OBJECTIVES

• How a resistor network can function as a voltage signal averager
• Application of Millman's Theorem

SCHEMATIC DIAGRAM

ILLUSTRATION

INSTRUCTIONS

This deceptively crude circuit performs the function of mathematically averaging three voltage signals together, and so fulfills a specialized computational role. In other words, it is a computer that can only do one mathematical operation: averaging three quantities together.

Build this circuit as shown and measure all battery voltages with a voltmeter. Write these voltage figures on paper and average them together (E1 + E2 + E3, divided by three). When you measure each battery voltage, keep the black test probe connected to the "ground" point (the side of the battery directly joined to the other batteries by jumper wires), and touch the red probe to the other battery terminal. Polarity is important here! You will notice one battery in the schematic diagram connected "backward" to the other two, negative side "up." This battery's voltage should read as a negative quantity when measured by a properly connected digital meter, the other batteries measuring positive.

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