Published November 5, 2026

ESP32 Light Meter with an LDR Module (Soldr Draft)

A learning light meter: ESP32 reads an LDR module on GPIO34/35 and streams raw values over Serial.

BeginnerFull instructions provided21

ESP32 Light Meter with an LDR Module (Soldr Draft)

Things used in this project

Hardware components

Espressif ESP32

Story

We asked Soldr for firmware to wire an LDR sensor module to an ESP32. Soldr drafted an ESP32 sketch on GPIO34 (analog) and GPIO35 (digital), 12-bit ADC (0–4095), 115200 baud, 500 ms samples. At the time Soldr warned the parts weren't carded in the build yet, so the draft hadn't been pin-checked against a parts list inside Soldr. We ran it on a real ESP32 + LDR module on the bench anyway. In the session clip the live plot is moving while the powered module is held next to the laptop; Serial streams [DATA] ldr_raw=… digital=….

This is a learning meter, not a calibrated lux meter. The raw number depends on the module's divider, the pot on the digital output, and how you aim the LDR. Use it to see relative light, not to quote lux.

Compoden and Soldr are one company: Compoden is the India parts store, Soldr is the agent that drafts the firmware and wiring. Disclosure: Compoden is our store. We ship inside India.

Things you'll need:

ESP32 30-pin Dev Board (CP2102): https://compoden.com/products/esp32-30-pin-development-board-cp2102-wifi-bluetooth
LDR Light Sensor Module: https://compoden.com/products/ldr-light-sensor-module-for-arduino-microcontroller-projects
Jumper wires: https://compoden.com/products/jumper-wire-combo-male-to-male-male-to-female-and-female-to-female
USB cable for the ESP32 (Micro-USB on this board)

Wiring:

LDR VCC → ESP32 3V3

LDR GND → ESP32 GND

LDR AO → ESP32 GPIO34

LDR DO → ESP32 GPIO35

GPIO34/35 are input-only. Turn the module pot until DO flips cleanly when you shade the LDR.

Firmware:

esp32_ldr_light_meter.ino

// ESP32 + LDR sensor module light meter
// Prompt used in Soldr: "write a code to interface an ldr sensor module with an esp32"
// Pins match the Soldr draft (GPIO34 analog AO, GPIO35 digital DO).
// Module: VCC, GND, AO, DO. Many modules: DO HIGH = dark (threshold pot).

const int AO_PIN = 34;  // ADC1, input-only
const int DO_PIN = 35;  // ADC1, input-only OK as digital read

void setup() {
  Serial.begin(115200);
  pinMode(DO_PIN, INPUT);
  analogReadResolution(12);  // 0..4095 on ESP32
}

void loop() {
  int ldr_raw = analogRead(AO_PIN);
  int digital = digitalRead(DO_PIN);
  Serial.print("[DATA] ldr_raw=");
  Serial.print(ldr_raw);
  Serial.print(" digital=");
  Serial.println(digital);
  delay(500);
}

Credits

Compoden

3 projects • 1 follower

Compoden is an AI-powered electronics store for makers, students, and builders in India.

ESP32 Light Meter with an LDR Module (Soldr Draft)

Things used in this project

Hardware components

Story

Code

esp32_ldr_light_meter.ino

Credits

Compoden

Comments

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ESP32 Light Meter with an LDR Module (Soldr Draft)

ESP32 Light Meter with an LDR Module (Soldr Draft)

Things used in this project

Hardware components

Story

Code

esp32_ldr_light_meter.ino

Credits

Compoden

Comments

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