Soldering an EMF Detector

The workshop is based on an open-source free circuit for the Elektrosluch detector of electromagnetic waves in sound spectrum with an inbuilt amplifier published in Weekend Project: Listen to Weird Sounds from Electromagnetic Fields and developed for LOM audio* by the amazing inventor Jonáš Gruska under the CC NC-BY-SA licence. Gruska allowed the use of this circuit for noncommercial purposes. It is thanks to his work that we may all have access to this amazing device for field recording and raising awareness of electromagnetic smog. And to uncover the unexpected acoustic beauty, versatility and textures that we find in the virtual aural space unfolded by this machine.

To his circuit from the Makezine, I’ve added a simple on-(off) switch and an LED indicator to promote the battery life of the device. For an easier educational process, I projected a PCB in KiCad free software for the design and simulation of electronic hardware. I also added a proposal for a simple ergonomic soft casing from recycled materials and one small laser cut front.

* The device Elektrosluch 3+ is sporadically available at LOM audio, Bratislava, Slovakia.

Tools for Soldering

There are several different printed circuit boards. In the original instructions, Gruska used a protoboard, which is a single-use board that does not have prefabricated paths between individual holes. Stripboard has prefabricated linear paths but no other connections between the holes. Breadboards are used for test experiments and may be used multiple times but are highly unstable. 

The prefabricated PCBs may be through-hole boards or surface mount devices (SMD). Our PCB for EMF detector is a hybrid between through-hole and SMD in which all our elements are soldered through-hole apart from a switch that is mounted on the board.

Soldering iron is used for melting and mounting the elements on a printed circuit board (PCB). 
Attention! Handle with care. The iron is 350°C! Always put it back on the stand.

Solder is the metal that melts at a temperature in the approximate heath range of the soldering iron. If you ever make a mistake, you should remove redundant melted solder with a desoldering wick. Solder is the metal that melts at a temperature in the approximate heath range of the soldering iron. If you ever make a mistake, you should remove redundant melted solder with a desoldering wick. 

Attention! Some soldiers are more toxic than others. Ideally, we use lead-free solder Cu6Sn5 that has fewer carcinogenic side effects. Nevertheless, always breathe out when melting the solder and blow the fumes away from you. 
Attention! Time your soldering technique well so that the elements are firmly melted into the PCB. An unsuccessful connection is called “a cold solder” as electricity will not run through it. To make a good solder, you should heat the surface equally as the element. However, you also must not overheat it, as you might either damage the element or burn the surface. A rule of thumb is that a successful solder melts onto the surface while a cold solder stays like a lump on the surface.

Pliers are used for holding electronic components so that your hands don’t get too near to the heated soldering iron.

With cutters, we remove access “legs” of the electronic elements that stick out of the PCB.

Wire strippers are used for stripping the insulation from cables to expose the metallic part so that you can solder it to the surface. 

Third-hand is a little helper that may prove handy when attaching the electronic elements in a through-hole PCB.

Making a PCB in KiCad

KiCad is a free software suite for electronic design automation that facilitates the design and simulation of electronic hardware. It took about 30 hours of clicking around KiCad to project the PCB for this workshop and I only recommend KiCad for someone who already has some knowledge in electronics as it requires drawing schematics with new symbols, adjusting a PCB layout with suitable components of the correct size and possibly some aesthetic features (print, shape), manufacturing file viewing, engineering calculation, Gerber files export for the print run, etc.

Electronic schematics are symbolic representations of electronic elements, their values and characteristics indicate what role they play in an electronic circuit, how they are positioned, directed and what are they connected to. The vocabulary for schematics is quite simple as it contains the elements that we will get to know in our circuit (resistors, capacitors, LEDs, opamps, outputs, ground), however, the connections between them, the values we chose and the (audio) result they produce requires a higher level electronic knowledge. For now, it is enough to just become a little more familiar with this symbolic language. 

Download the KiCad Gerbers bundle for ordering a printed PCB.

EMF detector DIY kits

The kits’ goody bags contain all the building blocks for the EMF detector including the casing. Silkscreen print by Pirate Piška.

Bill of materials (BOM)
PCB — 1x KiCad designed printed circuit board (PCB)
IC1 — 1x chip i.e. integrated circuit (IC): OPA2134 (optional: TL72, OPA1662)
IC1 — 1x 8-pin IC socket
L1, L2 — 2x inductor (22mH, vertical type)
R1, R22x — 1kΩ resistor
R7 — 1x 10kΩ resistor
R5, R6 — 2x 100kΩ resistor
R4, R3 — 2x 390kΩ resistor
C1, C2, C3, C4 — 4x 2.2µF 10V electrolytic capacitor / polarised
C5, C6 — 2x 100µF 10V electrolytic capacitor / polarised
SW1 — 1x push button/switch
D1 — 1x Light Emitting Diode (LED) BATT — 1x 9V battery holder
BATT — 1x 9V battery
AUDIO — ½ stereo 3.5 mm jack cable
JUMPER — white
SHRINK TUBE — yellow
ZIP-LOCK — black ♥

The layout shows the position of elements on the board. Pay attention to the SW1 and J1 that are soldered from the bottom side of the PCB.


Please follow the order of soldering and pay attention to special ways in which some of the elements should be bent. Trust me, it will spare you a lot of time and frustration with desoldering.

Elements by order of soldering [Detailed instructions: EMF-soldering-order.pdf]
PCB 1x KiCad designed printed circuit board (PCB)
IC1 1x 8-pin IC socket
IC1 1x 8-pin IC socket
IC1 1x 8-pin IC socket
R1 R2 2x 1kΩ resistor
R7 1x 10kΩ resistor
R5 R6 2x 100kΩ resistor
R4 R3 2x 390kΩ resistor
C1 C2 C3 C4 4x 2.2µF 10V electrolytic capacitor / polarised
C5 C6 2x 100µF 10V electrolytic capacitor / polarised
L1 L2 2x inductor (22mH, vertical type) Attention! Bend the legs at a 90° angle.
SW1 1x push button / switch
D1 1x Light Emitting Diode (LED) Attention! Bend the legs at a 90° angle.
Audio ½ stereo 3.5 mm jack cable
Battery 1x 9V battery holder
Jumper white
Shrink tube yellow
IC1 1x chip i.e. integrated circuit (IC): OPA2134 (optional: TL72, OPA1662)
Battery 1x 9V battery
ZIP-lock black ♥

Soldering IC socket

Do not yet insert the IC as integrated circuits are sensitive to heath and we want to apply as little heat to it as possible. You will add the IC into the socket right at the very end of your process.

Attention! The IC has orientation, which is indicated with a small circle or a half-moon shape. Make sure it is orientated upwards.


Soldering of passive components: Resistors

In electronic circuits, resistors are used to reduce current flow, adjust signal levels, divide voltages, among other uses. Most commonly, beige coloured resistors have 4 stripes and a 5% +/- tolerance, which means that their resistance may vary quite a bit, which is not significant for opamps like ours but may prove to be too inaccurate for some modular synthesisers. A more accurate resistor with 5 stripes and a 1% +/- tolerance is usually blue.

I recommend using one of many Resistor Code Calculator App on your mobile device to monitor your resistor colour and value. However, the most accurate way to measure the resistors is by using a multimeter. Set your multimeter to the Ω symbol, adjust a black probe to one leg of the resistor and the red probe to the other leg. Make sure that you are not touching the resistor with anything else as your body’s resistance might affect the measurement.

R1, R2: 1KΩ R3, R4: 390KΩ R5, R6: 100Ω R7: 10KΩ

Soldering of passive components: Capacitors

A capacitor is a device that stores electrical energy in an electric field that has charging and discharging cycles. In audio electronics, we most commonly use ceramic, polymer, electrolytic and tantalum capacitors. The first two are very inexpensive and have no polarisation, meaning that they work the same no matter how we place them on the board. In our EMF detector, we will only use electrolytic capacitors. Pay attention, there is a small plus symbol + on the board indicating where the longer leg of the capacitor should go. Once we cut the legs, we may observe a gray stripe, which always indicates the opposite, the minus symbol –.

C1, C2, C3, C4: 2.2µF C5, C6: 100µF

Soldering of passive components: Coil

An inductor is a passive electrical component that opposes sudden changes in current. Inductors are also known as coils. Inductors slow down current surges or spikes by temporarily storing energy in an electromagnetic field and then releasing it back into the circuit. An inductor blocks or impedes changes in current and functions as a low pass filter. An inductor has no orientation.

Attention! Bend the legs at a 90° angle.

L1, L2: 22mH 

Switch (SMD)

An electronic switch is an electronic component or device that can switch an electrical circuit, interrupting the current or diverting it from one conductor to another. We have the most simple on-off switch with two legs that have only one function, to switch off the battery. However, there are much more complicated switches that may have many functions at once. Such switches usually have 4, 6 or even 9 legs. Solder switch as a surface mount part. First, add some solder to the surface, then melt the part onto the surface.


SRT cable: 3,5 mm jack (shrink tube)

A stereo audio cable is composed of three parts that indicate how each of the two stereo signals travels through the circuit. The Sleeve is connected to the ground (GND) of the circuit board. The Ring is connected to the right inductor and right opamp, and the Tip is connected to the left inductor and the left opamp. If you wish to isolate your cables (especially the Sleeve that has no internal isolation) you may use the shrink tube if you burn it ever so slightly with a lighter. If you use a cable that has different colours or you’re not sure which one is which, you can simply test it with a multimeter. On the 3.5 mm jack the Tip is the end of the jack, followed by the Ring and the Sleeve is closest to the plastic part.  Set the multimeter to the bleep sign (audio speaker icon) place one probe on the ring and measure which wire responds to it. To make sure, place the probe to the sleeve and measure which wire responds to it. The Sleeve should always correspond to the uninsulated wires. 


Battery holder for 9V

Every battery or battery holder has a +/- orientation. It is a convention that red always indicates plus +, while black always indicates ground or minus –. 

Attention! Never solder anything on the board while a battery is connected to prevent shortcircuit.


Light Emitting Diode (LED)

A diode is a two-terminal electronic component that conducts current primarily in one direction; it has low resistance in one direction, and high resistance in the other. A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The red colour diode is an ancestor of all light diodes as the technology only allowed for the emission of low-intensity infrared light. 

Attention! Bend the legs at a 90° angle.



The older version of the PCB has one quirk. To make the switch work properly, we have to make a so-called bridge connection with a wire between the left Switch SMD surface and the upper hole of the R6 indicated with a letter B on the back-side of the PCB panel. Use strippers to remove the insulation from the tips of the wire and use a shrink tube if you wish to insulate it later.

Connecting active components: opAmp2413 / TL072 (8 pin)

Carefully place the first four legs into the IC socket, bend a little to also place the four legs on the other side, then firmly push the IC into the socket.

Attention! The IC has orientation, which is indicated with a small circle or a half-moon shape. Make sure it is orientated upwards or you may burn the chip when connecting to the battery.


What is dual op-amp?

An operational amplifier, or op-amp, is a voltage amplifying device designed to be used with external feedback components (resistors and capacitors). Op-amps are linear devices that have all the properties required for DC (direct current) amplification and are therefore used extensively in signal conditioning or filtering. The difference for dual supply op-amps is that it can swing positive all the way to negative, capturing the entire AC (alternating current) signal cycle.

Connecting active components: 9V battery

Connect the battery to the battery holder while pressing the IC (chip) with your finger. If the IC becomes hot really fast, immediately disconnect the battery as such overheating signals a short circuit.

Press the switch!

a) If the LED turns on: Bravo! Connect the jack to your recorder, set the gain to a minimum (see In The Field with EMF Detector, page ??). Move the coils near a power source and listen. If you hear a squeak and a crackle: Bravo! If you don’t hear anything then troubleshoot.

b) If the LED does not turn on: Troubleshoot!

Testing and Troubleshooting

There are two basic rules of troubleshooting. The first is the empirical test. Go through all the solders that you made, recheck that none of them is cold. Pay attention that non of the connections that should not have been made were somehow melted. To remove extra solder from your board, use the desoldering wick. Recheck that all the right components are in the right place. Recheck the orientation of the electrolytic capacitors. If that doesn’t solve the problem, turn on the multimeter and check possible incorrect connections with the bleep sign (audio speaker icon). Next, check the resistance in the circuit, which should be around 4.5V on each side of the circuit. If you detect large discrepancies between one side and the other, pay attention to the solders that lead to the strange behaviour.


In DIY electronics, you must protect your device with well planned and well-fitted casing. There is nothing more frustrating, especially for a beginner, to come home from a workshop and realise that the cables have torn and you have no soldering iron to fix them. After you have tested your device and everything works fine, you may attach the 9V battery and audio cable with zip-locks through horizontal and vertical holes on your PCB to prevent them from tearing. 

For casing, you will need:

  • One recycled toilet paper core. You may use an acrylic colour of your choice and apply it with a sponge to make it prettier.
  • 15×15 cm anti-stress material such as bubble wrap, anti-stress foam, paper wrap.

Your device fits snuggly into a toilet paper core. Once you’ve squeezed it in, cover the front end with the plexiglass cover, make sure that the two coils fall into two bigger holes at the side and the LED fits into a small hole at the centre. Once everything is snuggly packed, glue the plexiglass to the paper core with instant glue. To fully protect the device wrap it into an anti-stress material of your choice. Fix it to the paper with a hot glue gun. Tug it into the open end of the paper core so that only the cable sticks out. For further protection, make sure you use the fabric gift bag to carry the device around.

Next step

To learn how to use the device, please refer to the second part of the workshop In the Field with EMF Detector.

Teaching materials were commissioned by konS – Platform for Contemporary Investigative Art and produced by Rampa Lab and LokalPatriot.