The Elektor TAPIR is an E-smog detector that can sniff out sources of electromagnetic radiation. It is not a precision instrument, but a handy tool to find out if something is radiating or not. Both cases are interesting. For instance, if a laptop power supply is not radiating anything, then it is probably not switched on, or it is dead, which explains why your computer’s battery doesn’t charge anymore. On the other hand, if you are experiencing interference where you don’t want any, you can use the TAPIR to find the culprit to switch it off or move away from it.

The TAPIR Is a 3D SMT Soldering Kit

The TAPIR comes as a kit of parts that you must assemble yourself. The kit includes everything you need to build a fully functional tool that you can carry around in your pocket. The only thing not included is an 1.5 V AAA battery.

Tapir kit
The TAPIR comes as a kit of SMD parts.

The kit is also interesting as an exercise to improve your soldering skills. The circuit uses SMT parts, which are somewhat more difficult to mount on a circuit board than through-hole parts. Furthermore, the TAPIR consists of seven small PCBs that must be soldered together to form the tool’s enclosure. Therefore, the TAPIR is a 3D soldering kit. Assembling the kit is explained in detail in the Construction Manual, with many photographs.

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The Circuit

The parts are packed in a nice black box with white print on it. The bottom of the box shows the TAPIR’s schematic and the parts list. The circuit is a simple three-stage low-frequency amplifier without any filtering. Therefore, high frequencies are amplified too. The non-linear properties of the transistors sort of down-convert these high frequencies, which makes them audible as strange noises that you can listen to with the included earphones.

Two Antennas: H & E

The TAPIR comes with two antennas that you must also assemble yourself (only the earplugs are preassembled). The H-field or magnetic field antenna consists of an inductor with ferrite core soldered on two pieces of wire. This antenna is suitable for detecting magnetic fields created by for instance other inductors, transformers, and loop antennas.

The second antenna, a rod antenna with a loop at the end, detects electric or E-fields. These are emitted by high-voltage transmission lines, EL backlights and old mopeds passing by.

Electromagnetic fields are a combination of both fields, mostly occurring in the ‘far field’ at a larger distance from the generating object.

Bear in mind that when you hold the TAPIR in your hand, your body is part of the antenna, which may increase the audible hum level.

elektor tapir with circuit
The TAPIR makes display updates audible.

Useful Debugging Tool

Although detecting electro smog is one possible use of the TAPIR, I find it much more interesting as a debugging tool. Especially with the H-field antenna (the inductor) it can help you detect all sorts of activity in a circuit. The absence of any activity means that the circuit is not doing anything. A running crystal oscillator produces high-pitched noise; you can hear a display being updated, and you can even hear current flowing. Move it slowly over your smartphone with its display switched off, and you will hear all sorts of sounds, from noise and squeaks to pulsating bleeps.

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The E-Field Antenna

The E-field antenna seems less useful. Sometimes the results are better when you create a physical connection between the TAPIR and the source by touching it with your other hand. This can remove mains hum. The E-field antenna is also very sensitive to touch. Sliding a finger over it is clearly audible. I assume this is due to static electricity created in the insulator around the wire.

To get good results in these situations, it is, of course, best to switch off as many other electromagnetic sources as possible. LED lighting can be quite a strong source of interference, but also large transformers. Also, be aware that conducting surfaces may reflect interference, potentially pointing you in the wrong direction when looking for a source.

Discover the World With Electromagnetic Ears

In an interference-free environment, like outside in a garden, you only hear soft noise. But as soon as you get near a mains cable, the TAPIR starts humming. Walk around the house and you’ll hear all sorts of noises. An induction cooktop when powered on produces great PWM sounds. I find it quite magical, actually. Of course, it takes some practice to learn what the sounds mean and how to interpret them properly, but once you do, you have a neat little gadget that can help speed up repairs and debugging.

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