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Electronics Projects: How to Divide Voltage with Resistors

Here is an interesting property of resistors that is useful in electronic circuits: if you connect two resistors together in series, you can tap into the voltage at the point between the two resistors to get a voltage that is a fraction of the total voltage across both resistors. This type of circuit is called a voltage divider, and is a common way to reduce voltage in a circuit.

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When the two resistors in the voltage divider are of the same value, the voltage is cut in half. For example, suppose your circuit is powered by a 9 V battery, but your circuit really only needs 4.5 V. You could use a pair of resistors of equal value across the battery leads to provide the necessary 4.5 V.

When the resistors are of different values, you must do a little math to calculate the voltage at the center of the divider. The formula is as follows:

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For example, suppose you're using a 9 V battery, but your circuit requires 6 V. In that case, you could create a voltage divider using a 1 kΩ resistor for R1 and a 2 kΩ resistor for R2. Here's the math:

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As you can see, these resistor values cut the voltage down to 6 V.

In Project 2-3, you build a simple voltage divider circuit on a solderless breadboard to provide either 3 V or 6 V from a 9 V battery.

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