7" Touch Screen Stops Sending Touch When 3v3 Pin is Plugged In

Question

I'm using python 3.4 to control the GPIO pins and using a GUI interface I made to interact with everything. I'm using a 16 channel relay to control some solenoids with the code. When I plug the 3v3 pin on the pi into the 5v pin on the relay the code works fine but the touch function of the touch screen stops responding. Mouse input still works fine. I need the touch to work as it will be the only input for the users.

I'm using a Pi b. My touch screen is the LANDZO 7 inch Touch Screen with 800x480 resolution.

Answer 1

I don't know how much of an answer this is, but here are my thoughts. I don't have the components you do, nor do I have the engineering degree to tell you for sure, but this is something I'd look into if I was in your place.

The 3.3v shouldn't be taking 5v in. There's a possibility that you are overvolting the touch screen electronics, causing it to not work and eventually will destroy the controls for it. There is a 5v on the screen, so I'd suggest trying to use that instead. If you can't, then use a couple of resistors to change your voltage.

I've done it with a HC-06 BlueTooth device on an Arduino. It works.

I'm guessing that removing the grounds from your relay is causing a "backup", of sorts, in the current. The power can't flow as normal, so the screen is getting fewer volts, so you aren't overvolting the touch aspect (as much) so it's working. I'm thinking it's trying to backfeed maybe 1.5v from somewhere that's normally grounded, and viola, almost 3.3v (5v - 1.5v = 3.5v).

Answer 2

So, I removed the two ground pins from my relay and now it all works fine... This isn't really an answer to why this is happening but it is, if only temporary, a solution.