Guns and Lasers

Hi smart people,

I'm looking for some direction with an idea I had (born from laziness, as all good ideas are).
I like to have a plink with an air rifle every now and then, and have several paper based and knock down targets set up in my back garden. Unfortunately the paper based targets require my removal from the cosy warmth of my back door to the often wet and cold outside to retrieve the targets and check the hits (and the knock down targets don't show accuracy).

So I thought about an electronic target, did the google search, and it seems that type of target is stupidly expensive, and designed for ranges ... not the occasional sort of thing I'm looking for. I had a think about how to record a hit, and came up with a pressure pad type thing and a laser proximity thing (I use "thing" as I really don't know about this stuff). Kinda gave up on the pressure pad idea as there is not much that will stand constant abuse from a rifle and live to talk about it, so we're left with some sensor that can detect a pellet passing by at 850fps. I started looking at laser stuff, but am so out of my depth on this I really don't know what I'm looking at.

I got the mega for the extra inputs, but it wont be enough .... we're talking 100 photodiodes to try and catch the pellet passing (6mm pellet at 300 m/s) .... the photodiodes are up to the speed, but I have no idea how to read that many diodes. I looked at shift registers to reduce the number of inputs but how do I convert the output from the photodiodes to binary so the register can work?

As a bit of background, my electronics experience is limited to soldering ... everything else is a black art to me, the programming side I'm more than comfortable with.

Anyone want to help me expand this idea (and save me from the awful English weather)?

Cheers all


Google "ballistic chronometer"

I don't care about the speed, apart from being able to catch the pellet passing. I'm more concerned with accuracy, i.e. where the pellet crosses the laser matrix to determine location.

Update …
I’m going to try passing the output from photodiodes to a bunch of comparators, which then feed into a few PISO shift registers which can then be read by the arduino.

Does this sound feasible?

At 300Mtrs/sec you've only got about 20 microseconds (max) to detect a 6mm pellet. You'll have to detect in both the X and Y axes within those 20 microseconds to get an accurate position. Your code, even using interupts, will have to be minimal to allow two reads in that short space of time.

One option might be smaller targets.

Lots of people can hit a big sodding knockdown, but can you hit these tiny (1-2cm?) knockdowns Reg has soldered up?