Me and my group are making an interactive light installation that consists of 5 pressure pads which are basically made with two wooden boards, the insights of which are covered in aluminium foil and the outer (inner) boarders of which are covered with a spongy material so when someone steps on them the aluminium conductive sides touch and it basically acts like an on/off switch (as seen on one of the pictures attached below). The pads' surface is 31cm X 42cm in case that matters.
The basic idea is that each of the pads, once stepped on, activate an effect on a separate 3m long LED strip (all in all 5x3m = 15m SK6812 dense Led strips). When we started developing it, we were testing everything with push buttons instead of the pads. We used a Corsair CX500M ATX power supply to power the strips and the whole circuit (5V and 12A). Everything was working just fine but once we swapped the buttons with the pressure pads, the program started lagging at some point and stopped completely. To add more excitement to our problem, we also started getting electrocuted every time we try to switch the wires/resistors and try a different solution (with the power supply off). In order to reduce voltage on the pads/capacitors we swapped the 1K resistors with a 10K one however that resulted in none of the LEDs lighting up.
We are not the best at electronics as you might see and we really need your help, does anybody know what might be the problem and perhaps the solution? (We got the idea that we have basically created a gigantic capacitor out of our pressure pads and it's storing a lot of current that is causing the problem, but please correct us if we're wrong)
Here are some pictures of the pads and the whole circuit to get a better idea of what we're dealing with
You should not get an electric shock from a 5v or 12v supply.
If you are getting an electric shock (hopefully very mild) there must be a build up of static electricity to voltages that are high enough to cause damage to an Arduino.
It is also possible that due to some faulty or incorrect wiring mains voltage is able to get to your apparatus - that has the potential to kill you or your friends.
a serious fault with the power supply - this is potentially life-threatening.
static discharge from plastic parts of the sensors - not dangerous, but could damage the electronics.
If you switch off and disconnect the supply and still getting electrocuted its static. However this
test in itself could be dangerous. Do you have an alternative good power source?
Changing the 1k pulldowns to 10k was definitely a mistake, weak pulldowns mean more noise pickup.
Stick to 1k pulldowns but add 100nF capacitors in parallel to them. Also add 100nF between 5V and ground
for each sensor to absorb static discharge spikes.
The capacitance of 1 square metre metal plates 1mm apart in air is small, about 9nF, so shouldn't be a problem
with 100nF caps to decouple the supply and the output signal for even large area sensors like this.
It seems to be due to static discharge as it happened after we disconnected the power supply. We will try that, thanks a lot! What I still don't understand is tho, why did it work perfectly with the push buttons, without having any static discharge build up but the moment we switched the buttons with the two wires coming from each pad the problem came about?
What do you mean by 'electrocute'? (You are clearly not dead, so I don't think you have been electrocuted). Describe the sensation and explain where exactly you got it from.
There is nothing in your schematic that worries me, however, as the power supply is mains fed maybe it is leaking mains voltage into the output. Is the mains lead earthed, as in, is it connected to the safety mains earth in the mains plug*? Is the 0V output also earthed?
(We got the idea that we have basically created a gigantic capacitor out of our pressure pads and it's storing a lot of current that is causing the problem, but please correct us if we're wrong)
Yes, you created a giant capacitor, giant as in physically big, but tiny in terms of the energy it can store. Even if it was storing a lot of energy (it's not) the voltage would only be what you have available to charge it up to, 5V, which is harmless.
The "switches" should always be connected between an Arduino pin and ground, with a pull-up resistor from the pin to 5 V. Having the 5 V line running out on cables to other part is a bad idea unless absolutely necessary. Clearly it is necessary to run 5 V to the LED strips. Your code must respond to a LOW when the switch is closed.
Your description of "switched off" and "disconnected" in regard to the power supply is confused. An ATX power supply must be properly grounded using a three wire power cable and plug to a correctly installed mains outlet.
Static electricity causes a spark and sudden temporary "jolt" when touched, mains leakage causes a persistent "tremble" or "buzz" as long as it is touched.
Hello,
I don't know what is causing the issue but if you can't figure it out, you could side step the issue by putting your button between the two panels. When the user steps on the pressure pad, it will just activate the button inside the pressure pad.
