April 2026Guided SimulationBeginner

Build a Voltage Divider — Step by Step

A voltage divider is the most fundamental circuit in electronics. Two resistors in series, with an output taken from the middle — that's it. Yet this simple circuit appears in almost every electronic device. This guided simulation teaches you to build, calculate, and test one.

What We Are Building

graph TD VIN["Input Voltage (Vin)"] --> R1["R1 (top resistor)"] R1 --> VOUT["Output Voltage (Vout) — taken here"] VOUT --> R2["R2 (bottom resistor)"] R2 --> GND["GND (0V)"] style VIN fill:#1a3a4a,stroke:#00e5ff,color:#00e5ff style VOUT fill:#1a3a2a,stroke:#00ff88,color:#00ff88 style GND fill:#161b1f,stroke:#5a7080,color:#5a7080

The formula: Vout = Vin × R2 / (R1 + R2)

Step-by-Step Guide

STEP 1

Decide the Output Voltage You Need

Common use case: you have a 5V Arduino and a 3.3V sensor. You need to step the Arduino's 5V GPIO output down to 3.3V before it reaches the sensor's data input. Target: Vout = 3.3V from Vin = 5V.

Why this matters in 2026: Most microcontrollers (ESP32, nRF52840, STM32) run on 3.3V I/O. Many still-available sensors and displays use 5V logic. Voltage dividers are the low-cost solution for interfacing these different logic levels when a dedicated level-shifter IC isn't available.

STEP 2

Calculate R1 and R2

From Vout = Vin × R2 / (R1 + R2), rearrange to find the R1:R2 ratio:

💡 Imagine two people carrying a heavy box up a staircase: The total effort is 100%. If one person is twice as strong as the other, they carry ⅔ of the load. R1 and R2 divide the voltage exactly the same way — proportional to their resistance. Higher R2 means more voltage "lands" at the output.

R2 / (R1 + R2) = Vout / Vin = 3.3 / 5 = 0.66

So R2 / R1 = 0.66 / 0.34 = 1.94. Use R2 = 2kΩ and R1 = 1kΩ (standard values, ratio ≈ 2:1). Actual output: 5 × 2/(1+2) = 3.33V ✓

⚠️ Choose low enough resistance values. R1 = 1kΩ and R2 = 2kΩ draws 5V/3kΩ = 1.67mA continuously. Using 100kΩ and 200kΩ reduces this to 17µA — much better for battery circuits, but makes the output sensitive to loading by the 3.3V input (typically 50kΩ input impedance). Rule of thumb: divider resistance should be at least 10× lower than load impedance.

▶ Simulate Voltage Divider

STEP 3

Verify in the Simulator

Open the voltage divider simulation. Double-click R1 and change its value to 1kΩ. Double-click R2 and change to 2kΩ. Hover over the junction node to see the output voltage displayed in the bottom right.

Now add a load: right-click the output node and add a resistor to ground. Set it to 50kΩ (representing the sensor input). Watch the output voltage drop slightly — this is the loading effect.

STEP 4

Test with Different Input Voltages

Double-click the voltage source and change from 5V to 9V. The output changes proportionally to 9 × 2/3 = 6V. This demonstrates that a voltage divider scales the output linearly with input — it is always a fixed ratio.

This makes voltage dividers ideal for resistive sensor interfaces (NTC thermistors, LDRs, potentiometers) where you want a voltage that scales with the sensor's resistance change.

▶ Potentiometer as Divider

STEP 5

Add an Op-Amp Buffer

When driving a low-impedance load, add a voltage follower (unity-gain op-amp buffer) between the divider output and the load. This presents near-infinite impedance to the divider (no loading effect) while driving the load from a low-impedance output.

▶ Op-Amp Voltage Follower

When to add the buffer: Whenever your load resistance is less than 10× the divider resistance, or when you need the output to be stable regardless of how much current the load draws.

Frequently Asked Questions

What is the voltage divider formula?

Vout = Vin × R2 / (R1 + R2). R1 is connected from input to output node, R2 from output node to ground. Larger R2 gives higher output voltage.

Why does my voltage divider output change when I connect a load?

Adding a load in parallel with R2 reduces the effective value of R2, shifting the output voltage downward. This is the loading effect. To prevent it, add an op-amp voltage follower buffer between the divider and the load.

Can a voltage divider replace a voltage regulator?

No. A voltage divider output voltage changes with load current. A voltage regulator maintains stable output voltage regardless of load. Use a regulator (LM7805, LM317) whenever you need stable voltage under varying current demand.