Medium

IR Proximity Detector

An infrared LED emits invisible light, and a phototransistor detects it bouncing back off a nearby object — the principle behind "touchless" sensors on many appliances.

Circuit Diagram

+9V 220R IR LED emitter → aimed at same target ← R Phototransistor BPW41N Q BC547 C → LED E → GND 220R indicator LED IR LED + phototransistor pair: reflection off a nearby object lights the indicator

How to Build It

  1. Place the infrared-emitting LED on the breadboard, with its limiting resistor, connected to the positive rail.
  2. Position the phototransistor (BPW41N) next to the IR LED, both aimed at the same target area.
  3. Connect the phototransistor's collector to the positive rail through a resistor.
  4. Connect the phototransistor's emitter to a BC547 transistor's base.
  5. Connect this transistor's collector to a visible indicator LED and then to the positive rail; emitter to GND.
  6. Power the circuit and bring a hand close to the sensor — the indicator LED should light up.

Bill of Materials

ProductCodeQty
Phototransistor 112211 1
LED component OSI3CA5111A 1
LED (3/5/10mm, SMD, power) l-934ID-12V 1
Resistor DR47K-8/9 2
Transistor (incl. IGBT) — 1
← All kits  ·  Newsletter