Going back to basics here, as I’ve come across a problem which I can’t seen to rectify and maybe I am missing the obvious.
I made a solder hot plate thingy for soldering SMD, using this link:
23VAC to 5VDC psu - 5V input to the Nano, everything else is running from 3.3v, supplied via Nano
Solid State Relay
K type thermos
Iron base - 230VAC, supplied via psu and the SSR
The purpose is to solder smd components. It consists of two displays, one being a temp which the user selects using the pot and another screen which shows whether the device is ‘off’ ‘preheat’ and ‘reflow’ and shows the current temp from the thermo. So, one oled is used with two different screen, showing which state it is in or another screen comes up when the pot is adjusted.
A push button is pressed and the relay is powered, letting 230VAC power the iron, this is until the temp reaches 150C and then the button is pressed when ready, with the temp being raised to the set point. As the screen is flickering between displays, the button can not be selected.
Originally I thought my issue was solely the thermocouple, as when the CS connection is removed, the display stopped switching between screens. The thermocouple outer is braided metal, which I thought may be the problem. So I wrapped the outer with heat resistant tape, as when the braided metal initially touched the iron, there was static, but only upon movement of the thermo. Obviously, the end of the thermo is directly touching the iron, which didn’t cause static and it is reading fairly accurately and settles.
Further fault finding led me to checking all connections, which appeared to be fine. The I discovered if I remove the 5V supply from the psu and power the Nano via USB, the oled settles and it all works perfectly.
So, this must be a ground issue? I tried a common ground between the electronics and the psu and the iron but nothing changes, still the same issue. I tried grounding the sheath of the thermo and still the same problem.
I could just use separated supplies and never worry again but this is bugging me and I’m not sure what else to try and I don’t like the idea of a common supply without some sort of protection, such as a optocoupler, maybe?
Anybody shed any light? Thank you