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I'm building an interactive disco dance floor. Like the light up dance floors from the 70's, but each floor panel should be able to detect when it's being stepped on and possibly light up to show this. I'm trying to figure out the best method of step detection.

  • Each panel will be about 12" x 12".
  • Since people will be dancing, the panels should not move (a little bit of give is okay)
  • Optical detection from above will detect the person blob, but not which panel is being stepped on (not accurate enough).
  • Optical detection from below is expensive and could be troublesome if trash is on the floor.

What is the best approach here? Ideally the panel wouldn't move at all and could just detect that someone is standing on it. Although, I'm okay with the panel having a bit of give, if needed. The important thing is that people can dance normally without feeling like the floor is unstable.

Here are some of the ideas that I have come across:

Piezo Sensor: I believe the voltage spike with these sensors is momentary and wouldn't let the system know if the person is still standing on the panel.

Custom Foam Pressure Sensor: Based on this instructable, an analog pressure sensor made from foam. It is cheap, but probably not well calibrated or consistent between panels.

Accelerometer Tap/Click Detection: Would require a heavy enough stomp to detect and the feedback would be momentary, like the piezo sensor, and not let me know the person is still standing on it.

Air Pressure sensor: A sealed rubber tube with a barometric pressure sensor under the panel. This would require me to build the sealed tube and could be susceptible to damage or leaks over time.

Capacitance Detection: Would it be possible to detect capacitance change over the panel? Even if the person is wearing rubber or leather soled shoes?

Load Cell: Like this one from SparkFun. Would report when someone is standing on it and how much of their weight is applied. Currently my favorite option.

Ideally I want to go with something that will work consistently and will last.

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  • \$\begingroup\$ Capacitive detection requires very little circuitry and works through panel and shoes. \$\endgroup\$ – venny Sep 3 '14 at 0:18
  • \$\begingroup\$ Cool. Where/what would it not detect? \$\endgroup\$ – Jeremy Gillick Sep 3 '14 at 0:19
  • \$\begingroup\$ Unless differential electrode arrangement is used (probably not possible here), it will drift slowly so it can not detect people standing still for a long time. \$\endgroup\$ – venny Sep 3 '14 at 0:26
  • \$\begingroup\$ How about total internal reflection (like a fingerprint sensor)? The idea is you bounce light off of the top surface from the bottom and anything pressing against the surface would prevent the light from reflecting. Could be tricky to get it to work over the entire surface. Load cell would be my second choice if this method doesn't work. \$\endgroup\$ – alex.forencich Sep 3 '14 at 0:40
  • \$\begingroup\$ Total internal reflection would require a camera under each panel, right? I love how it would work without any moving parts, however, I'd be worried with the cost per panel. \$\endgroup\$ – Jeremy Gillick Sep 3 '14 at 0:47
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Taking Nick's idea a step further, how about 2 plates with a slightly compressible dielectric between them. Then you've got a pressure controlled variable capacitor. Build a simple RC oscillator and measure the frequency of the output.

Drive the whole thing with a microcontroller that calibrates itself when it's first turned on so it self-adjusts for the compression of the foam over time.

This would be similar to your foam pressure sensor. You could probably use the same self-calibrating approach with that as well. At startup, you'd measure the resistance of each panel and make that your unloaded value. A significant drop in resistance tells you somebody's standing on the panel.

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  • \$\begingroup\$ I like that. I'll have to try it and see. It sounds like a nice low cost way to detect this. Especially since fine precision isn't required. \$\endgroup\$ – Jeremy Gillick Sep 3 '14 at 5:37
  • \$\begingroup\$ You may even envision something like a keypad matrix. But you would need to design it in such a way that multiple tiles in the same row/column can be 'depressed' simultaneously. pcbheaven.com/wikipages/How_Key_Matrices_Works \$\endgroup\$ – Nick Sep 3 '14 at 17:43
  • \$\begingroup\$ I think I'd probably set up a 16 x 16 grid using 2 pairs of 8 channel multiplexers or a 1-of-16 selector and 2 pairs of 8 channel muxes. I'd build the tiles so they would have an enable line, and would only oscillate when enabled. Then I'd write a program that would cycle through each tile, enabling a row, then reading the signals from each tile in that row. Keyboard matrixes get confused when multiple keys are depressed at once (As you alluded to, @Nick. \$\endgroup\$ – Duncan C Sep 5 '14 at 23:14
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Use standard capacitive touch sensor for that. No movements, no mess, no layers of dielectric and complicated mechanical setup.

There are tons of ready made solutions, with auto-calibrate, and pretty stable detection. They can detect objects trough the glass, and also trough shoes.

http://www.atmel.com/products/TouchSolutions/bsw/qtouch.aspx

I have good experiences with the old QT110, now Atmel has bought the full product line, I suspect this is the new part: http://www.atmel.com/devices/AT42QT1010.aspx

It is however important to keep in mind two gotchas:

  • you need the sensor plate to be transparent (since you have lights from below, right?)
  • you shall keep the capacitance (i.e. the total surface) of the sensor plate low

To meet these requirements, use a wire mesh instead of a solid sensor plate. Mosquito nets made of thin condictive wires work the best. Mount them directly to the lower surface of the traslucent glass tiles (glass or policarbonate or anything like that), and they're practically transparent so you can light up the dancefloor from below.

Note that you can tune the sensitivity of the IC with capacitors (see the datasheet). I have achieved repeatedly stable detection trough 4 cm of solid wood (automatic staircase light).

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