Induced Interference on Arduino Uno in a Car?


I'm new here so don't really know the etiquette ect.. so tell me if I'm doing it wrong!

So I'm currently trying to log cylinder head temperature on my 2CV using thermocouples and I keep getting a lot of strange characters on the screen:

These characters appear only with the engine running, with or without thermocouples connected. It also happens with the Arduino anywhere in the car, powered by the laptop or the car. I tried in vain to decrease the interference (I assume that's the cause) by covering the coil in foil, this had no effect at all.

A bit about the Car - There's very little to it electrically, essentially an alternator, lights front and rear and one wasted spark coil.

A bit

I'm using an Adafruit Thermocouple Amplifier MAX31855, an Uno Rev 3 Board, an LCD screen like this - and will be using one of these to record the data I gather, but I can't read Japanese (I assume thats what it is??) so could some one here advise me on what is causing this and how to eliminate it?

Thanks for any help you can offer!

Any electronics in an automotive environment is subject to serious noise and downright circuit-destroying voltage spikes. The spark coil can induce spikes of hundreds of volts into a piece of wire and the starter motor creates tremendous surges. Everything needs to be protected by transient surge suppressors, and unless you have reasonable knowledge of electronics, working with very low level signals like thermocouple amplifiers is going to be nearly impossible. Your entire circuit needs to be in a grounded metal box and all leads into it need to be shielded and/or decoupled with capacitors. The thermocouple cable has to be heavily shielded.

A bit of time with Mr. Google is recommended, for example "automotive surge (spike) protection". The issues have been discussed on this forum a number of times.


I'll try a grounded box, decoupling capacitors and shielding over the weekend. With regards the grounded box, I guess OEM ECUs are different to Arduinos as (apart from engine ECUs) the majority seem to be housed in plastic casings?

Non-resistor spark plugs will create this interference. Typically the plug will have an "R" in its name to designate the presence of a resistor.

See this thread for more info: