Browsing around on AVRfreaks' forum I stumbled upon this thread about an Airsoft Round Counter to display the number of remaining rounds when playing airsoft. This is obviously a cool idea and the thread inspired me to want to make one myself.
In the thread people discussed using everything from a simple switch attached to the trigger over photo interrupters and photo reflectors to accelerometers for detecting when a shot is fired. There is also a link to this page on the Design Decisions Wiki where a group of people have designed an "Airsoft Electronic Ammunition Counter" with detailed design considerations and requirement analysis and timing calculations. Excellent work and a great source of inspiration for this project.
My initial considerations for this project:
- Enclosure. Everything should be mounted to an airsoft gun and it shouldn't be the size of a shoe box!
- Component count. This ties in with number 1 above: if this is to be small enough to be portable I have to keep the component count down so the final PCB is of a manageable size. (Yeah yeah, "use SMD". Right, I'll do that in phase 2.)
- Ease of use. This will be used in skirmishes so it should be real easy to use. No re-flashing of the processor to change settings, easy to attach to a weapon and so on.
So far I have settled on the following basic components:
- ATTiny 2313-20PU. I could probably get by with a smaller ATTiny but since I already had a couple of these lying around I went with those...
- Four-digit 7 segment display
- Maxim 7219 CNG display driver.
- Wide-gap photo interrupter
Off to EAGLE for some schematic drawing and thence to the breadboard for figuring out how photo interrupters actually work...