Cree LED bedside light with auto off using a 555 timer.

[steed5000]

Question: can you have a 555 timer circuit with one on button and one off button (cancel/reset) that consumes no curent when the timer has ended, like when you make a latching circuit with relays??

The project: I have built a bedside lamp with 3 white Cree LED's running off a small bank of PP3 9v batteries (I have loads of used but good batteries due to my job in instrumentation), 3 LEDs in series, they have a rating of 3-3.2v each so total of 9v together, I built a PCB using the 555 timer with one start button (starting the timer for 40mins) and one cancel button to turn off the lamps but the power used by the timer in the ‘off’ state still pulls a current and after a day or so my power pack is dead, if I just use a normal on/off switch the batteries last for 6 months+ when using for 1 hour a night max, basically I need a circuit that when the timer cuts off the PCB is not drawing any current at all until pulsed again to start the timer and when finished it cuts off again, I think this could be a handy thing for other people as I have seen similar problems on other forums. I will attach a diagram so you can see the project so far.:|

 

[srizbf]

Re: Cree LED bedside with auto off using a 555 timer.

better attach yhe diagram , so that members can give advice.

 

[scanman]

Hi steed5000,

I would try experimenting with an SCR in series with the battery supply.
The SCR should self commutate when the LEDS go out (current of 555 is too
small to keep SCR conducting). The "ON" switch pulses the gate of the SCR.
The "CANCEL" switch is NC pushbutton in series with the SCR.
Need to measure "off" current and select correct SCR.

Regards,
Scanman

 

[srizbf]

to reduce the current consumption , when LEDs are off is
to include a transistor in series with + line and controlling its base voltage with the sample from pin3 of 555.

in which case the switch SW1 may be moved across the series transistor .