velocity101:
Hello all, I need help/advice building a circuit that will detect a bullet passing over its sensors
I did that years ago. We were trying to get schlieren images of a supersonic bullet passing through a column of heated air. The idea was to trigger at the muzzle of the rifle, then do a set time delay, then fire the laser to take the picture. I used a CMOS 4538 timer IC to do the delay (no microcontroller involved)... but I'll tell you what we tried to DETECT the bullet.....
First attempt: Infrared LED and detector. FAIL. The muzzle flash of the rifle was much brighter than the IR LED and not predictable in timing, so the laser firings were all over the place.
Next attempt: Aluminum foil strip across the muzzle to be broken when the bullet exited. FAIL. The column of air in front of the bullet ruptured the foil long before the bullet came out.
Next attempt: 30 gauge wire (wire wrap wire) as a "break switch". Partial success, but pieces of the wire came along with the bullet and each little piece had it's own shockwave along with the bullet. End result: FAIL.
Next attempt: An electrical contact to detect when the hammer contacted the firing pin. FAIL. The response time of the cartridge (time from primer strike to bullet exit) was not consistent.
Next attempt: Accelerometer attached to the barrel near the breech to detect the pressure pulse of the firing cartridge. SUCCESS!!! That worked, and it was quite consistent (only varied by a fraction of a microsecond between firings).
Lastly.... I think you are going to need a hardware timer to do your bullet sensor. A microcontroller is way too slow. By the time the micro sees the pulse and runs the code that says "I saw it", the bullet will be 100 yards downrange. Of course, I'm talking about a Mach 3 RIFLE... if you are measuring PISTOL bullets which barely break Mach 1, then maybe you have a chance.
Good luck!