Light, sound and IR sensors

Sensors are how a project notices the world. Many simple sensor modules work the same way, so once you learn one, you know most of them.

Two kinds of output

• AO is analog. It gives a changing voltage, read with analogRead().
• DO is digital. It goes HIGH or LOW when the level crosses a limit, read with digitalRead().

The small blue screw on the module sets that limit. Turn it slowly with a small screwdriver while watching the Serial Monitor.

Light sensor (LDR)

An LDR changes resistance with light. It is more resistant in the dark. On its own it needs a 10 kΩ resistor to make a voltage divider, and modules include this already. Use it for night lights and sun tracking.

Sound sensor

A small microphone turns sound into a signal, and the module reacts to loud sounds. Its output is a short pulse, so check it often in your code, and avoid long delay() calls that could miss a clap.

IR sensor

One part shines invisible infrared light and another watches for its reflection. A pale surface reflects well and a dark line reflects little. Line-following robots use this.

• Keep the sensor a few millimetres above the floor, as the project says.
• Strong sunlight contains infrared and can confuse it.
• Shiny or black objects may not be seen.

A method for every sensor

1. Connect VCC and GND, checking the voltage first.
2. Print the raw value to the Serial Monitor.
3. Note the value in both conditions, such as dark and bright.
4. Pick a threshold halfway between them.

An ESP32 takes 3.3 V on its pins. Power a sensor from 3V3, or reduce its output with a divider.