Here is very simple circuit in which the LED becomes ON only after a preset time the power supply is switched ON. When the power supply is switched on the transistor will be OFF. The capacitor now charges via the preset R3 and when the voltage across C1 is sufficient, the transistor switches ON and LED glows. The ON delay depends on the value of POT R3 .You can increase the time delay by increasing the resistance of POT R3.
This circuit alone may not have much practical applications but this can be used in many other projects where a delayed ON indication is required.
Circuit diagram with Parts list.
- Assemble the circuit on a genral purpose PCB.
- The circuit can be powered from a 10V DC power supply.
- Anyway you can use from 6 to 18V for powering this cicuit, but you need to adjust the POT R3 for getting the required delay.