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Circuits

Voltage Dividers

Split a voltage into a smaller voltage using two resistors. Essential for reading sensors and level-shifting signals.

What is a Voltage Divider?

A voltage divider uses two resistors in series to produce an output voltage that's a fraction of the input voltage.

The Circuit

Vin ─── [R1] ─── Vout ─── [R2] ─── GND

The Formula

Vout = Vin × R2 / (R1 + R2)

How It Works

The input voltage is divided proportionally based on the ratio of the two resistors. If R1 = R2, the output is exactly half the input.

Example: Reading a Photoresistor

5V ─── [Photoresistor] ─── A0 ─── [10kΩ] ─── GND

As light changes, the photoresistor's resistance changes, which changes the voltage at A0. The Arduino reads this changing voltage with analogRead().

Common Uses

  • Reading variable-resistance sensors (photoresistors, thermistors, force sensors)
  • Level shifting (e.g., 5V signal to 3.3V)
  • Creating reference voltages
  • Battery voltage monitoring

Design Tips

  • Use 10kΩ for the fixed resistor when reading most sensors
  • The output impedance (parallel combination of R1 and R2) should be low compared to the input impedance of what you're connecting to
  • For level shifting, calculate the exact values needed
  • Don't use very large resistors (noise) or very small (wastes power)