Equipment
Arduino Uno R3
DS18B20 1 wire temperature sensor
2 channel opti isolated relay
basic 8x2 char LCD
3 momentary buttons (menu, up, down)
9VDC 650mA wall wart
110v fan (it is running through a transformer to step down the voltage and make fan run slower, fan was existing)
I am making a digital aquastat for a wood boiler. This is an existing wood boiler, I am replacing the mechanical aquastat with this one, The aquastat will control a draft fan and overheat zone.
The LCD display is multi function, during normal run it tells current temp, and fan on or off state.
The buttons control a menu for setting fan on temp, fan off temp, overheat temp, F or C and saving options.
Also while not in the menu one button allows for viewing max temp, min temp, and overheat count, the other button allows you to reset the counters.
Relay 1 of controls the fan, Relay 2 controls the overheat (basically turns on a blow off zone)
This was bench tested extensively with no problems with EMI affects from turning on and off the relays.
As I am sure you have guessed ounce installed I started to have problems with EMI when relay 1 fan would turn off, this would cause the display to become garbled. Although the arduino would continue to work cycling the fan on and off.
To track where this interference is coming from, I removed the wall wart and powered the arduino from a 9v battery and ran dozens of cycles with no problem, when I reinstalled wall wart and problem immediately returned.
I understand this is from an inductive load but I am confused by how this is affecting the arduino and or display and how to correct this..
The wall wart is powered from an outlet separate from the power supplying the fan
I am using this wall wart Wall Adapter Power Supply - 9VDC, 650mA (Barrel Jack) - TOL-15314 - SparkFun Electronics
I do not have enough experience with snubbers to know what I am doing but, I did cut the ends off the wall wart and added a home made snubber (47uf & 180r) This did not work and I think it might have made it worse.
Thank you for any assistance you can provide.