He suspected EMF interference so as a quick first step he decided to throw together an EMF detector using an Arduino.

A total of 10 I/O pins (D2–D11) of the Arduino UNO is used to drive a 10-LED bar graph display (LDA-B10ZX). Here, the bar graph is wired to digital pins of the Arduino through 470R current-limiting ...

Professional equipment is often very expensive, but building an EMF detector yourself is not even that difficult: just take a look at Arduino expert [Mirko Pavleski]’s convenient hand-held ...