Basys3 switch issue

[justinkb]

I bought a Basys3 on Amazon and just received it.

I've been playing around with it a bit and it's a cool device, but I just noticed a weird issue with SW6 and SW2. Their signal output is usually clean as high when on, but if I approach those switches with my finger within half a centimeter (even not touching them), that output becomes erratic, flipping constantly. (It's almost magical, if anyone has a definitive explanation for this behavior, please reply) I have found out I can get the same behavior from all the other switches, too, if I position the switch around the middle between on and off. This leads me to believe SW6 and SW2 have bad solder jobs or something, which makes them behave while in the on position as if it is set to the "middle" position (obviously, middle position doesn't exist as defined behavior for such a switch I guess).

Is this a known issue with Basys3 boards, that some switches aren't properly functioning? Guessing I can't do RMA since I bought it on Amazon. Is this easily fixable by resoldering this myself? I happen to have hundreds of the exact switches used in the board from a project from years ago.

[justinkb]

I *think* I managed to determine this was a purely mechanical issue with the switches. I used a plastic pry tool to press down on the top metal contacts of the SW2 and SW6 switches while they were in the on position and they work better now. Still not perfect: while putting them into the on position, they still sometimes very briefly output a low signal while they have already output high signal initially

[JColvin]

Hi @justinkb,

Yes, what you described sounds like a mechanical issue where the tabs weren't completely set into place on the switches so that they were a bit more in that undefined state so probably any stray capacitance in your finger was changing the measured state of the switch. This isn't exactly the same thing, but you can read about a similar phenomenon here: https://electronics.stackexchange.com/questions/87233/why-does-an-led-light-up-when-i-touch-it.

As for the brief low signal when you turn a switch from "off" to "on", that would normally be classified as bouncing, and unfortunately is just an inherent property of mechanical devices like switches and buttons. It can be resolved though either a low pass filter in hardware (not readily possible with the Basys 3) or can be done through HDL, though I'm not sure if you already were aware of this detail and were asking about something else.

Let me know if you have any questions.

Thanks,
JColvin