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I want to make a laser hunt type game with my son using Nerf Guns. I can modify the Nerf bullet to put some sort of device on the top of the bullet (obviously something not too heavy). It would be easy enough to put a small magnet on the tip of the bullet.

I want to make a vest that can detect being hit by the Nerf bullet. It could contact with the magnet or some other device to detect that contact has been made.

Can anyone point me in the right direction of what devices can be used for this purpose?

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    \$\begingroup\$ search for "reed switch". I don't know how much would such a vest cost though. \$\endgroup\$ – Vladimir Cravero Apr 7 '15 at 9:02
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The idea I'd investigate for doing it is to have a conductive vest which uses principles of capacitance, where the bullet would impart a charge stored on it to the vest. This could make for extremely cheap vests and relatively cheap bullets; also they would be very light and robust. I expect the issue to overcome would be the best way of storing charge on the bullets. But using FET transistors which are very sensitive to small charges would mean the bullets may need minimal static charge. Although how then to protect the FETs from damaging static electricity may be a bit of a dilemma. It may even be possible for the bullets simply to become charged merely by passing through the air.

A magnetic system might be doable if you have something like arrays of small coils on the vest, which when the magnet approaches at speed, would induce a current/voltage. The problem is the weight and cost of the vests could be prohibitive. Also the vests might be delicate.

Using light could be a problem, as with the magnetic system, because unless the bullet emits a large amount of light, you would need a lot of sensors on the vest. That is, unless you can find a material that directs light from around the vest to a couple of sensors. Something perhaps along the lines of a number of fibre optic cables, or a material with an equivalent property.

An extension to the first idea, perhaps have bullets that behave a bit like RFID tags. A conductive vest could be used to energise the bullet, via radio waves or similar; While the bullet is near the vest, a coil and/or tuned circuit in the bullet is energised by the frequency of the vest. The vest then detects a change sent back by the bullet, or perhaps the modulation effect of the bullet on the vest's own oscillation. This idea definitely needs significant refinement, as it is way beyond my experience.

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    \$\begingroup\$ One other thought for the first idea: perhaps the piezoelectric effect could be used so that on impact the bullet generates a charge - similar to how cigarette lighters create the spark when the button is pressed. \$\endgroup\$ – CL22 Apr 7 '15 at 12:52
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    \$\begingroup\$ and as a bonus it might even give you a little 'tingle' so you know you've been shot :) \$\endgroup\$ – brhans Apr 7 '15 at 14:37

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