A handheld device to measure electromagnetic fields

Measuring Electromagnetic Fields With Just An Arduino And A Piece Of Wire

April 17, 2022 by Robin Kearey 9 Comments

Electromagnetic interference problems can be a real headache to debug. If you need to prove what causes your WiFi to slow down or your digital TV signal to drop, then the ability to measure electromagnetic fields (EMF) can be a big help. 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 electromagnetic field detector.

The basic idea is quite simple: connect an antenna directly to an Arduino’s analog input and visualize the signal that it measures. Because the input of an ADC is high impedance, it is very sensitive to any stray currents that are picked up by the antenna. So sensitive in fact, that a resistor of a few mega-Ohms to ground is required to keep the sensor from triggering on any random kind of noise. [Mirko] made that resistance adjustable with a few knobs and switches so that the detector can be used in both quiet and noisy environments.

Making the whole device work reliably was an interesting exercise in electromagnetic engineering: in the first few iterations, the detector would trigger off its own LEDs and buzzer, trapping itself in a never-ending loop. [Mirko] solved this by encasing the Arduino inside a closed, grounded metal box with only the required wires sticking out. The antenna’s design was largely based on trial-and-error; the current setup with a 7 cm x 3 cm piece of aluminium sheet seemed to work well.

While this is not a calibrated professional-grade instrument, it should come in handy to find sources of interference, or even simply to locate hidden power cables. You can view this as a more advanced version of [Mirko]’s Junk Box EMF Detector; if you have a second Arduino lying around, you can use that one to generate interference instead. Continue reading “Measuring Electromagnetic Fields With Just An Arduino And A Piece Of Wire” →

A Simple EMF Detector And Electroscope You Can Make From Junk Box Parts

January 10, 2022 by Dave Rowntree 47 Comments

2N2222 devices used, but practically any junkbox NPN will do

Electromagnetic fields are everywhere, all around us. Some are generated naturally, but in vast majority of cases, it’s we humans that are generating them with artificial, electronic means. Everything from your mobile phone to the toaster will emit some sort of signal, be it intentional or not. So we think it only befits the general electronics-orientated hacker to have some way of sniffing around for these signals, so here is [Mirko Pavleski] with his take on a very simple pair of instruments to detect both static and dynamic electromagnetic fields.

CMOS clock input connected directly to the antenna. Warning! ESD damage risk!

The first unit (a simple electroscope) uses a cascade of 2N2222 NPN bipolar transistors configured to give a high current gain, so any charge near the antenna will result in increasing currents in subsequent stages, finally illuminating the LED. Simple stuff.

The second unit relies on the extremely high input impedance of the old-school CMOS 4017 decade counter, which is likely of the order of 100 MΩ or even more. Normally you would not leave such a CMOS input floating, or even connect it with too long a PCB trace — lest it pick up a stray signal —but for detecting alternating EM fields, this appears to work just fine. Configured as a simple divide-by-ten, when presenting 50 Hz AC, the LED can be seen to flash at 5 Hz.

Simple stuff, and this scribe has all those exact parts in the junk box, so will be constructing these shortly!

We’ve covered electroscopes for years, here’s a modern twist on a famous classic experiment, and some hair-raising experiments to get you started.

Continue reading “A Simple EMF Detector And Electroscope You Can Make From Junk Box Parts” →

Perceiving Invisible Forces With An EMF-Detecting Dress

October 3, 2014 by Kristina Panos 9 Comments

In June of 2014, [Afrdt] spent two weeks on a boat as an artist-in-residence in Linz, Austria. During that time, she created a dress that detects EMF waves and outputs them to vibration motors and a headphone jack.

[Afrdt] started by making two EMF coil antennas and sewed them to cuffs that snap together. She crafted fashionable fabric stripes that both conceal and carry the cables from the coils to an Adafruit FLORA that’s sewn into the body of the dress. The wearer experiences haptic feedback via vibration motors in the chest, and sonic feedback from a mini female headphone jack built into the collar. The zipper functions as a low-pass filter and volume control for the jack. One side bears resistive tape and runs to the FLORA, which is programmed to play an 800Hz tone. The other side runs to the headphone jack via conductive thread. As the zipper is opened, the pitch increases to toward the maximum pitch of 880Hz.

She drew inspiration for this project from [Aaron Alai]’s EMF detector project and built the code on top of it. Broader documentation and many more pictures are available both at [Afrdt]’s site and the residency program’s site.

This project is an official entry to The Hackaday Prize that sadly didn’t make the quarterfinal selection. It’s still a great project, and worthy of a Hackaday post on its own.