Well... Done.
Design complete. Everything is working. I ended up building a TINY variant of this circuit which fitted on the back of a pushbutton and then replaced the brightness potentiometer in the red-dot-finder with the button. It works brilliantly and with a bit of black epoxy it may even look original. Push button, red dot comes on for 60 seconds. What more could you ask for?
A kit maybe? Yes a kit!
If I can get enough interest in a common kit for these I'll offer them up. So how about it guys. Who wants one?
Right now I have two variants of the design.
Tiny Pushbutton Version:
This is designed to insert into the red-dot-finder. It does not include a battery. Install would involve splicing this between the battery and the red-dot. Simply cut both the battery leads, connect the battery + to the pushbutton, connect the laser + to the pushbutton also, connect the battery - to GND, and connect the laser - to the MOSFET Drain. Then figure out some way of gluing it in. Benefits of doing it this way is you can make it all in one inside the red-dot-finder. Downsides is you'll need to disassemble it.
Larger Self Contained Version:
This design is self contained, designed to be mounted externally to the red-dot-finder and has only 2 connections to be made which can be made directly to the red-dot-finder's battery terminals. It's bigger, it's about $3 more expensive to produce, but you can use it without any modifications to the red dot finder other than figuring some way of connecting some wire to it's battery terminals. This version also comes with two different population methods. If there's interest in this I'll give people the choice of a blank PCB which they can populate with either through-hole or SMT devices. The board layout will happily cover either, except for the mosfet which will stay as a SOT23 part, however these are really easy to solder even for SMT (the leads are very far apart so good luck trying to short it out or doing something silly like that). All parts can be sourced from RS Components, but most are also available from Jaycar for the through-hole variant.
Anyway let me know if you want one below and which version you want. If there's overwhelming support for one version I'll forget the other existed. I'll see about getting some circuit boards made up.
As for a case, you're on your own.
