This is the exact same idea behind automatic streetlights and your car's automatic headlights, sense how dark it is, and switch a light on or off accordingly. We'll wire up a Light Dependent Resistor (LDR) into a simple voltage divider, read it with the ADC, and use that reading to automatically turn an LED on in darkness and off in bright light.

2. Scope

We'll build a voltage divider using the LDR and a fixed resistor, read the resulting voltage with ADC1, and compare that reading against a threshold to decide whether it's dark or bright. This reinforces the ADC skill from Experiment 3, applied here to a light sensor instead of a potentiometer, and introduces the voltage-divider trick you'll reuse for several other resistive sensors later on.

3. Prerequisite

3.1 Hardware

• STM32 Nucleo-F070RB development board

• LDR (Light Dependent Resistor)

• Fixed resistor (10kΩ typical, to form the voltage divider)

• LED + 220Ω resistor

• Breadboard and jumper wires

• Micro-USB cable

3.2 Software

• STM32CubeMX (standalone)

• STM32CubeIDE

• ST-LINK USB driver