Resistor Voltage Divider – A Simple but Essential Circuit

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Resistor Voltage Divider – A Simple but Essential Circuit

If there’s one circuit you’ll keep coming across in electronics, it’s the resistor voltage divider. Simple, reliable, and everywhere, from measuring voltages to dimming LEDs, it’s one of the first building blocks worth learning.

What is a Voltage Divider?

A voltage divider is just two resistors connected in series across a voltage source. By tapping the middle point between them, you “divide” the voltage into a smaller, useful value.

Formula:

Vout=Vin×R2R1+R2V_{out} = V_{in} \times \frac{R2}{R1 + R2}

Where:

  • VinV_{in} = supply voltage

  • R1 = resistor connected to input

  • R2R2 = resistor connected to ground

  • VoutV_{out} = output voltage between R1 and R2

Demo 1: Measuring a Higher Voltage

Say you want to measure a 9V battery with an Arduino (which only tolerates up to 5V).

  • Choose R1=10kΩR1 = 10kΩ, R2=10kΩR2 = 10kΩ

  • Output will be:

Vout=9V×10k10k+10k=4.5VV_{out} = 9V \times \frac{10k}{10k + 10k} = 4.5V
For this circuit we place the two resistors in series, then the point between the resistors is where we take our reading or output to other devices. This is our voltage divider.

Demo 2: LED Brightness Control

Hook up a 9V supply, then:

  • R1=1kΩR1 = 1kΩ

  • R2=470ΩR2 = 470Ω

  • Output = ~3V, just right to drive a red LED with a safe current-limiting resistor.

This is a neat way to experiment with how resistor ratios change brightness.

Again the two resistors are connected in series, with the larger resistor connecting to the +ve rail on the breadboard, and the smaller to the -ve rail. The point between the resistors is where the anode of the LED connects to, then on the cathode of the LED a link is made back to ground.

Why It Matters

  • Used in sensors (scaling signals).

  • Essential in analogue-to-digital conversions.

  • Great for biasing transistors and op-amps.

You’ll keep seeing it in real circuits wherever different voltage levels to the supply are required as it is a quick and easy circuit to build.

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