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# Timer light switch circuit

Tiny Timer Light Switch presented here is a simple transistorised electronic timer which drives a high efficiency white LED for a finite time out. This circuit is very useful for in-car reading etc. The circuit works off 12 volt dc supply. After construction, fit the unit at a suitable location inside your car and power the circuit from the in-dash standard cigar lighter socket. The timer light switch is ultra simple, economic, straight forward and self explanatory.

How the timer light switch works?

Normally T1 is turned off by P1 and R2. When the trigger switch S1 is pressed the base of T1 is connected to the +12V supply via R2. Now T1 turns on and this action turns on the next transistor T2 which in turn energises the white LED (D2). Resistor R4 limits the operating current of white LED (D2).

When the switch is pressed is current also flows into capacitor C1 (through R1) and charges it. So when the switch S1 is released the charge in the capacitor C1 keeps T1 turned on until the charge has decayed away through R2 and P1. You can easily increase the ouput on time by increasing the resistance of the potentiometer P1.

## Timer Light Switch Circuit Diagram

##### Related Tutorials

• dilsath

I need a circuit which can supply current for a minuet (1 millisecond)time and then stop for 5 seconds . Please help me.

For example to make a signal light working every 5 seconds

• ALex

I did it and it works! I used 4 AA batteries but plan to use it as a switch to turn on a toy at a science fair for only 40 seconds so kids can leave it on if they want to go somewhere else (they certainly will). Toy runs on 6V but I also will use a hair drier plugged to 110V. Shall I put the relay were the LED is? Thanks

• Dillon Chaffey

A simpler approach would be to use a monostable multivibrator approach, such as the one pictured to the right on this page:

http://en.wikipedia.org/wiki/Multivibrator#Monostable_multivibrator_circuit

This allows for a simpler and easier to understand circuit layout. Also this method allows one to adjust the time the light remains on for by using the formula below:

t = ln(2)*R2*C1 (seconds)

• Mechste

Hi, I am a marine fish keeper and my tank requires that I turn off the filtration system while the fish are fed. At the moment this is done manually and the pumps are off for around 15 minutes. As is the case with human error there are times when it gets forgotten and can be left off for hours which is not good for the eco system. I would like to use your Timer light switch circuit as above but with a normally closed contact relay switching the pumps off when the button is pressed for 15mins or so then back on automatically removing the human element. I can see the relay would replace R4 and D2 but I would like to power it with a 9volt battery. Could you help with component choice to complete such a project. I am good with a soldering iron and understand the principles of how components work just not good on the maths as to the best use of what parts.
steve

please if any one can help me with a circuit diagram to be able to send out radio waves that will submerge another radio broadcast signal

• Amit kumar

• mario

Hi, What’s the maximum time interval this circuit can produce? Would it be possible to have it on for a couple of hours? Say overnight? 5-8 hours? thanks

• raga khan