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I'm thinking about putting together something simple for my young son's soccer team. I'd like to build a simple circuit that could be placed on/underneath the laces of their shoes and plays a sound when the kids kick the ball on the laces.

Any ideas on what would be the simplest route to do something like this? I'm wondering what kind of contact sensor would work best and how bulky I'd have to make things to produce a sound loud enough for the kids to hear.

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  • \$\begingroup\$ It sounds (no pun intended) like you are looking for some sort of shock sensor (accelerometer) to detect the impact of the kick. The problem that I see here is how do you limit the impact detection to just the kick event and not detect the impact of the foot/boot on the ground? \$\endgroup\$ – uɐɪ Jan 22 '10 at 10:08
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A Piezoelectric sensor is enough for the detection of a kick.

http://en.wikipedia.org/wiki/Piezoelectric_sensor

They are cheap, easy to attach to a shoe and you can even use it as a buzzer to produce the sound.

This simple circuit will help you:

http://www.discovercircuits.com/DJ-Circuits/motionalarm2.htm

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  • \$\begingroup\$ I'd agree this is definitely the most economic method. The Piezoelectric buzzers are also fantastically sensitive, but would not react to airborne sound. However beware of handling the bare piezoelectric disk as they are very delicate. You won't want to use a sealed Piezoelectric disk in a plastic case, you will need to snap off the case, or buy one without a case. When using the Piezo as a pickup you want to attach the bare element directly to the surface you wanna detect vibration in. I'd use hot glue if it's permanent, you need a good solid contact... \$\endgroup\$ – Jim Jan 22 '10 at 11:28
  • \$\begingroup\$ ...Try not to snap the wire connections on the piezo disk, as trying to re solder them ruins the ceramic layer and the disk wont work anymore. A small amount of hot glue on the wires leading to the piezo will stop them from moving about and snapping off. \$\endgroup\$ – Jim Jan 22 '10 at 11:32
  • \$\begingroup\$ Those MSI sensors aren't disks, they are a flexible film, and quite robust. \$\endgroup\$ – Leon Heller Jan 22 '10 at 13:03
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I'd try something simpler - you just want to detect when the ball presses on top of the foot, which would require nothing more than a large, thin pushbutton.

Not many off the shelf solutions for that, but you can take a small surface mount pushbutton, sandwich it between two pieces of plastic, and then the plastic surface becomes the pushbutton. You can make this plastic disc as large or as small as you want, which will determine how precisely the soccer player must hit the ball to trigger it.

It should be less susceptible to false positives than many other shock detection solutions such as piezo or accelerometers, which might also be triggered with a particularly hard kick that isn't on the surface of the shoe.

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    \$\begingroup\$ I agree that a switch in the front of the shoe is a much simpler and more robust solution. \$\endgroup\$ – endolith Jan 24 '10 at 22:44
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I agree that the piezo sensor that PPVI suggested is a very cost effective way to go at less than $3 ea. However I would suspect it would not be discrete enough to distinguish between a ball being struck on the laces versus the toe or instep. I am a long time soccer coach as well and understand the precision you are looking for. Although it would be a much more expensive alternative I think you could use a softpot membrane potentiometer. Sparkfun has them for about $13ea. Check them out Here

However for the price difference you may want to try the piezo first.

Good luck and let us know how it works.

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