Timer Circuit

[Dodgecaliber]

Hi boys and girls,

 

Looking for a little circuit where I push a momentary button and it turns on a light for around 20 seconds, I can find plenty 230v switches, but Im after something 12/24v that will do the job.

 

Any suggestions?

[Matthew Robinson]

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!

[Jivemaster]

Scrapyard, car interior light delay unit?

[adam2]

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.

[Brian]

If you want the easy option - a PCB kit from Maplin or another one.

[KevinE]

Go to an electrical wholesalers and get a din-rail mounting timer, they are around £20