DIY EMF meter from £15 worth of Maplin bits - guide and testing results

Right, so I was fed up paying £60+ for commercial EMF meters that are mostly plastic and unreliable. So I built my own from components I got at Maplin (total cost: about £15) and it actually works better than some of the branded ones I've tested.

Here's what you need:

- Arduino Nano clone (£3 from eBay)
- LC oscillator circuit (£2)
- LCD display (£4)
- Coil of wire (literally any coil, I used telephone wire)
- Battery pack (£2)
- Breadboard and connectors (£4)

The principle is simple: you measure electromagnetic field strength by detecting oscillations in a tuned LC circuit. Nothing fancy. I've tested it against a commercial meter and the readings are within about 10% of each other, which is honestly better accuracy than you'd expect for the price.

I'll post the circuit diagram and Arduino code in a follow-up post. Anyone who wants to give this a go, happy to help troubleshoot.

This is brilliant, mate. I've been wanting to build something for ages but didn't know where to start. The cost is the real advantage here - if you lose it on an investigation or it gets damaged, you're not out £60.

Quick question: what's your frequency range? Commercial meters usually measure 50Hz-2kHz, does yours?

I'm not technical enough to build this myself, but I'm impressed you got it working for that price. The commercial stuff is a massive markup. Would you consider selling kits? Not trying to make you do unpaid work, but I'd genuinely pay £25-30 for a working unit.

I've tested it against a commercial meter and the readings are within about 10% of each other

Which commercial meter though? Because a lot of them are rubbish anyway. The real test would be comparing it to professional lab equipment, but that's probably not feasible. Anyway, decent DIY project. Respectable engineering.

Are you planning to account for false positives from household wiring? Because if you're investigating in a normal house, you'll get massive readings just from the electrics. The commercial meters have some filtering built in. Did you account for that in your design?

This is exactly the kind of practical advice this forum should have more of. Cheers for sharing the design. I'll give it a go when I've got time. Worst case, I learn something about electronics. Best case, I've got a working meter for nothing.