100 Seconds Duration On Switch with Touch Control by LM555

Description:

This is a touch controled switch which keeps the circuit on about 100 seconds after touching the plate connected to the 2 numbered pin. At the end of this time duration, relay releases and the circuit gets to off position.

The impedance of the trigger input of the 555 timer IC is very high and the inductive voltage on the human body is enough to trigger it. The circuit works based on this principle. You can use a piece of metal as a plate. The circuit can be used in toy circuits, buzzers or any project that is suitable. You can adjust the duration time by changing the R1 and C1 values.

Automatic Lamp Control with Light Sensitive Switch

Description:

The circuit above is an light sensitive automatic switch which functions in absence of light. The IC 4060 works as an oscillator and the generated signal is applied to the base of T4 transistor. Phototransistor T3 is in conduction by existence of light and it keeps the T5 transistor's base at ground potential.

When no light reaches the phototransistor, it gets in insulation. T3 reaches positive potential through 22kohm. T4 and T5 both gets in conductance. The oscillator signal reaches the optic coupler and lamp(s) shines.