EMF EXPLORER

Build your EMF Explorer Badge

Everything you need to assemble, understand, and troubleshoot your kit - written for explorers of all skill levels. Estimated build time: 1–2 hours.

New to soldering?

Take a few minutes to read through a soldering basics guide before you start. Two good options:

  • Full Solder Comic (PDF) - a friendly illustrated guide
  • Or refer to the infographic below, showing how to heat the pad, add solder, and let heat spread evenly
Soldering basics infographic - heat the pad, add solder, let heat spread evenly
Soldering tip: Keep your iron tip tinned to prevent oxidation, which reduces solder adherence and heat transfer. Clean the tip with a sponge or brass cleaner, and always leave fresh solder on the tip when not in use.

Safety first

💨

Good ventilation

Avoid inhaling solder smoke. Exhale while soldering to blow fumes away, and work in a well-ventilated area or use a fume extractor.

🧼

Wash your hands

Avoid eating or drinking while soldering - solder may contain lead. Wash hands when you're done.

🥽

Careful cutting

When trimming leads, hold the lead or aim it downward to avoid flying metal. Wear safety glasses, and keep your iron away from anything but its stand while hot.

Step 1 - Gather your supplies

  • Soldering iron (40–80W recommended)
  • Solder
  • Heat-resistant work surface
  • Wire snips for trimming leads
  • Two AAA batteries
  • Headphones with a 3.5mm audio plug

Step 2 - Place and solder components

Your component layout photo is your build map. Red text labels on parts indicate they must be inserted in a specific orientation - read the description for each part before placing it. Solder in stages and check your work as you go. Zoom in on the diagram as needed.

Rear-of-board component callout diagram

Prefer video? Watch the full video assembly guide on YouTube.

Step 3 - Trim leads & inspect

  • Trim as you go

    Hold the lead with your other hand, or aim it downward, before snipping - and wear safety glasses.

  • Inspect every joint

    Make sure all solder joints connect securely and look shiny/smooth. Reflow solder as needed to get a solid bond.

Step 4 - Power on and test

Connect the batteries, plug in your headphones, and hold your EMF board close to an electronic device - a cellphone, a power cable, even your soldering iron. You should hear that device's EMF signature in your headphones.

Step 5 - Go exploring!

Listen to different devices and notice the differences. How do Bluetooth headphones sound when connecting versus transmitting? What does a laptop touchpad sound like under your finger? Get curious about everything around you - the field guide below has ideas on what to listen to first.

What to listen to first

Hold your badge close to these everyday devices and listen through your headphones.

🔌

Power supplies

Detect the low-frequency hum given off by chargers, adapters, and power bricks.

💡

Light switches

Hear how a switch connects the power circuits running through the walls around you.

💻

Computers & monitors

Pick up the internal operational emissions of laptops, desktops, and displays.

🎛️

Dimmers & motor controllers

Dimmer switches and motor speed controllers produce distinctive variable-frequency noise.

📞

Telecom devices

Listen for the power circuit emissions of phones and communication equipment.

🎧

Bluetooth headphones

Hear the internal electronics at work - notice how the sound changes between connecting and transmitting.

📺

Remote controls

Pick up IR emitters and other emissions when a remote is in use.

🛴

...and beyond

Scooters, parking meters, vending machines, "open" signs - explore everything you can find.

Exploration challenges

New to listening for EMF? Try these starter challenges on your own or with a group:

  • The Bluetooth handshake

    Turn on a pair of Bluetooth headphones near your badge. Listen for the moment they connect to a phone - does the sound change?

  • The touchpad tap

    Hold your badge near a laptop touchpad. Tap and drag your finger across it - what does touch sound like?

  • The dimmer sweep

    If you have access to a dimmer switch, slowly turn it up and down while listening. Notice how the pitch shifts.

  • The street walk

    Take your badge outside. Parking meters, "open" signs, scooters, and streetlights all have stories to tell.

Learn more about the board and how it works

Who's it for?

This kit is for everyone curious about their surroundings. Wear it on a lanyard to light your way at night, or pick up headphones and start hunting for EMF signals. It's a great entry point into electronics - no prior experience required.

What is EMF?

Every conductive material can act as an antenna, picking up small currents from electromagnetic waves, which can be amplified and heard. Likewise, anything emitting electronic signals radiates them into the space around it - signals a coil of wire (like the inductors on this board) can pick up. Everyday household electronics tend to emit disturbances between 20Hz and 20kHz - right in the range of human hearing. EMF Explorer amplifies those signals by roughly 1000x so you can hear them clearly.

How does it work?

Inductors on the board detect EMF signals. When a changing magnetic field passes near an inductor, it induces a voltage - that voltage is amplified and sent to your headphones as sound.

Want to learn more?

How signals create magnetic fields

Watch this Veritasium video on how electronic signals create a magnetic field around wires to move electrons.

The electromagnetic spectrum

Read NASA's guide to the electromagnetic spectrum for the bigger picture.

Tune a real radio receiver

Explore a broad range of frequencies with the University of Twente's WebSDR tunable receiver.

Open the hood

Designed in KiCad - the badge artwork was built with vector layers in Affinity Designer, then converted into KiCad layers using Gingerbread. Explore the full design files on the EMF Explorer Badge GitHub repository - or read about it in Make: Volume 90.

EMF Explorer badge PCB artwork, UFO design with illuminated beam
EMF Explorer frequency monitor - real-time spectrum analyzer showing signal peaks

Try the frequency monitor

Plug your badge into your computer with a 3.5mm TRS to USB-C cable and see the frequencies it's picking up in real time.

EMF Explorer Zine cover - hand illustrated companion guide to the electromagnetic universe

Read the zine

The EMF Explorer Zine is a hand-illustrated companion to the badge - covering the science, the build, and the world of signals worth exploring.