Basic touch panel on an airsoft target

Hi Everyone,
I'm hoping someone can give me some ideas about the best direction to go with this project...It's really in its infancy but has been whirring around in my head for ages!

I've had the idea for a while now about creating a target for me to shoot with my airsoft gun (incase you don't already know, airsoft guns fire small plastic ball bearings.)

I was thinking about building a target and then having a really basic 'touch' style interface on it so I can interpret the hit location with an Arduino and feed that back to me at the top end of the range.

Current best idea I have is to use a couple of pieces of velostat hooked up to the Arduino so that when the target is hit, they give a difference in resistance to ground.

The only downside to that method is that I can't actually tell where I've hit on the target, only that I have hit somewhere because the velostat resistance changes with pressure so it's not an effective method of telling location, only pressure. The only way around that is to have separate pieces of velostat 'sandwich' for each ring of the target so I'll know which score I've hit, it's not exactly accurate though!

Does anyone have any better suggestions for me? I'd love to hear your thoughts so I can turn this dream into reality!

Thanks!

Maybe a supersized key matrix, like 50x50. The paintball impacting crisscrossing wires performs the keypress function. Keyboard scanning hardware/software then interprets where the impact occurred.

That's an interesting call, I'm just concerned about the chances of hitting in-between wires but I guess if each track was wide enough I could put each track almost butting up to each other so there's no 'dead space'...
So I could make the tracks out of 2 layers of velostat for the pressure contact and criss-cross them to give location.
Thanks!

How big is the target?

A grid of break beam sensors would be another solution - but the beams would have to be really close together (about 90% of the size of a bb, which is pretty small)/

Or a scanning laser sensor like those used in shooting chronographs:


They scan fast enough to catch the moment the ball impacts, and if you have two or more of them that overlap you can triangulate where the ball hit the target. Two of them opposite one another would result in a roughly square area where they're overlapping.

mmking:
That's an interesting call, I'm just concerned about the chances of hitting in-between wires but I guess if each track was wide enough I could put each track almost butting up to each other so there's no 'dead space'...
So I could make the tracks out of 2 layers of velostat for the pressure contact and criss-cross them to give location.
Thanks!

Yes, track width and density will determine resolution and hence the number of I/O needed. Actual wires contacting would give a definite on/off signal. IIRC, velostat gives you more of an analog variance depending on pressure. This may not be enough to definitively switch a digital input - requiring more signal conditioning.

wvmarle, thanks for the suggestions! I was just thinking something approx. 30cm round, the beam sensors sound a bit tricky due to the need for so many so close together! The scanning laser in theory would work well but I'm not sure I've got the skills for that! Lasers worry me that I'm gonna blind myself accidentally! haha

dougp, can you think of a medium that might work better than Velostat? I've only leant that way because I could basically put the 2 layers together without having to worry about any kind of spacer and rely on the impact to change the resistance compared to the baseline.

Thanks everyone for your suggestions and help, it's really getting me thinking!

mmking:
Lasers worry me that I'm gonna blind myself accidentally

Just remember: don't look in laser with remaining eye.

Anyway the lasers used in these applications are usually IR, and so weak they can't do damage.

mmking:
dougp, can you think of a medium that might work better than Velostat? I've only leant that way because I could basically put the 2 layers together without having to worry about any kind of spacer and rely on the impact to change the resistance compared to the baseline.

It's only a vague concept but I was thinking something like the flat flexible ribbon cable you might see on a printer carriage. I don't know if you can get that without insulation but if not, you could (tediously) scrape away the insulation at certain points and then the impact would press two intersecting wires together. I picture also a sheet of insulating material to keep the contacts apart when the impact pressure subsides.

Another path could be to etch a circuit board with the matrix and place switches over two intersections. Think of your TV remote keypad supersized. I wonder if anybody still make cricket switches?