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What is a Voltage Divider

A voltage divider uses two resistors to reduce a voltage. It is the simplest way to convert a 5V sensor signal to 3.3V for ESP32 or Raspberry Pi.

The Formula​

Vout = Vin × R2 / (R1 + R2)
    Vin ──┬── R1 ──┬── Vout
          │        │
          │        R2
          │        │
    GND ──┴────────┴──

Quick Reference: 5V → 3.3V​

R1R2Vout (Vin=5V)Use Case
1kΩ2kΩ3.33VCommon values
2.2kΩ3.9kΩ3.20VSlight margin for safety
10kΩ20kΩ3.33VLow current draw

Arduino Example: Read 5V Sensor on ESP32​

// 5V sensor output → R1 (1k) → ESP32 GPIO → R2 (2k) → GND
const int sensorPin = 34; // ADC pin
void setup() { Serial.begin(115200); }
void loop() {
  int raw = analogRead(sensorPin);
  float voltage = raw * 5.0 / 4095; // ESP32 ADC is 0-4095
  Serial.println(voltage);
  delay(500);
}

When NOT to Use a Voltage Divider​

  • Power supply — resistors waste power as heat. Use a voltage regulator (buck/boost).
  • High-speed signals — resistors add RC delay, degrading I2C/SPI above ~400 kHz. Use a dedicated level shifter (e.g., TXS0108E).
  • Precision analog — resistor tolerance (±5%) affects accuracy. Use 1% resistors or an op-amp buffer.