RE: upgrading an 35mm trail cam
For 50 bucks the 35 mm isn't a good deal in my opinion. The film costs alone have to be pretty high. Not worth it IMO.
but if you already have the camera and upgrade to digital might be possible. I used toknow ofsome homebrew camera sites that may help. I'll look in my bookmarks to see. You may just want to search the web for them too.
I think if you have the motion sensor and it triggers a switch to close then wiring it to a camera should be pretty easy. It depends on the camera too though.
Gool luck.