This post presents circuit which detects darkness using light dependent resistor (LDR) and produces a beep alarm by piezo buzzer. Circuit is based on 555 timer in astable mode to generate a square wave output.
Components
| No. | Component | Quantity |
|---|---|---|
| 1. | Power supply (5V - 9V) | 1 |
| 2. | 555 timer | 1 |
| 3. | Piezo buzzer | 1 |
| 4. | LDR | 1 |
| 5. | 2.2kΩ resistor | 1 |
| 6. | 10kΩ resistor | 1 |
| 7. | 1MΩ resistor | 1 |
| 8. | 1μF electrolytic capacitor | 1 |
| 9. | 100pF ceramic capacitor | 1 |
Circuit diagram
If the light drops below a certain level, a beep alarm is produced. The value of R1 resistor affects the level of light the LDR will detect and circuit will produce a beep alarm.
Designed circuit
Circuit is designed on a breadboard.
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