Circuit Diagram
How to Build It
- Position an ordinary LED (as the light source) facing the phototransistor, some distance away — this is the beam.
- Wire the phototransistor so that, normally (beam unbroken), it keeps a BC547 transistor OFF.
- Connect the BC547's collector to a buzzer and then to the positive rail.
- Connect the emitter to GND.
- Power the circuit — the buzzer should stay silent while the beam is unbroken.
- Pass a hand through the beam — the buzzer should sound immediately.
Bill of Materials
| Product | Code | Qty |
|---|---|---|
| Buzzer | LD-BZPG-2312 | 1 |
| Phototransistor | — | 1 |
| LED (3/5/10mm, SMD, power) | l-934ID-12V | 1 |
| Resistor | DR47K-8/9 | 1 |
| Transistor (incl. IGBT) | — | 1 |