Transistor RC-Delay LED

Circuit Diagram

How to Build It

1. Place the BC547 transistor on the breadboard.
2. Connect an electrolytic capacitor from the positive rail to the transistor's base, in series with a large resistor (the resistor and capacitor values set the delay).
3. Also connect the transistor's base to GND through a second resistor (discharges at start-up).
4. Connect the collector through a limiting resistor to an LED, then to the positive rail.
5. Connect the emitter to GND.
6. Power the circuit — the LED should stay off for a few seconds, then turn on by itself as the capacitor charges.

Bill of Materials