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Timer Circuit


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A 555 timer circuit.


Connect pins 4&8 to +v; 6&7 in between a timing resistor and timing capacitor (with one leg of the timing resistor connected to +v, and one leg of the timing capacitor connected to gnd. Connect the other legs together and to pins 6&7 of your 555); 2 to be pulled low when you want to trigger (remember to have a pull up resistor to +v to stop it floating); 3 is your output and 5 is not connected.


To work out time constant, use T=1.1 * R * C.


E2A: If you want it to power a relay (for high powered lights), beware of back EMF which will damage the chip!

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Or a time lag switch as often used for stairway lighting in blocks of flats.

If you get the older type, then the delay action is mechanical and will work on any voltage, AC or DC.

The newer electronic types will only work on AC at about the rated voltage.

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