Circuit to shut off power after a short time of turning on

timing

I've got a 3V button battery driving an led and a trembler switch functioning now. However, the sensitivity of the switch is giving me trouble because I need it to remain open when at rest in a horizontal and vertical state and only open when set into motion. This works sometimes but is very difficult to duplicate reliably. The answers to my last post helped a lot but I wanted to try one last tack. If I replaced the trembler switch with a tilt switch it would be 100% reliable to activate every time it was tilted from vertical, but would unfortunately remain on when horizontal which I need to avoid. I have tried to find a very small (I only have about a 1/2 inch of space to work with) tilt switch that is open in the vertical and horizontal planes. The best would be if I could find a component like that. Barring that, what would be the simplest possible way to alter the circuit so that it would turn off again after some short period of time like a second and only reset if the switch turns off again? Thanks for any help.
-Rory

On the comment regarding using a capacitor, how would I determine the correct capacity to choose besides trial and error?

Best Answer

There is no way around the switch drawing current if you need to continuously monitor it. However, there are two points that help:

  1. The current can be very small. With a 1 MΩ pullup driving a CMOS input, it will draw only 3 µA from a 3V supply. That is small even for some button batteries.

  2. You don't need to continuously monitor the switch. For most rolling ball motion switches, every 20-100 ms is good enough depending on your application. You can have a tiny micro wake up every 20 ms. It would turn on the pullup just long enough to take a reading, then turn it off again. The average current drain can be below a µA with this setup. That's less than the self discharge of some button cells.

Related Topic