[Garbz (Chris)]

Got a message from Allan recently who has the same problem I have, I got through CR2032 batteries about once every 2-3 weeks because I forget to turn the damn red-dot-finder off. So... electronics time:

The circuit is very simple needing only a few components. A pushbutton, a diode to prevent back charging, a capacitor and resistor store a charge and bleed that charge, and a MOSFET to act as a switch.

The entire circuit is powered by a 3V battery and the outputs of the circuit can go directly into the battery terminals of the red-dot-finder. Then it's just a case of leaving the red-dot-finder on and when you want to use it tap the pushbutton. It stays on for 60 seconds and then goes off.


Good things:
- Never forget power again.
- No battery use while off (MOSFETs leakage current measured in nanoAmpers)
- Cheap
- Potential for some hardcore miniaturisation (will work on that if the circuit works in practice).
- No modification to red-dot-finder needed as this circuit can connect directly to the battery terminals.

Bad things:
- More electronics.
- MOSFET choice limited due to requiring a threshold voltage less than 2.7V.

Will try to source some parts and get this built this weekend.