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Project Notes

#124 EMRDetection/RFDetectorProbe

A simple RF detector mounted in a pen.

Here’s a quick video of the detector in action, probing a 555 astable oscillator running at a few hundred kHz:



This is a quick build of an RF detector based on the circuit presented in dazaro3’s RF Pen detector video. The best explanation of how this works is possibly w2aew’s video concerning a similar circuit.

I used 1N60P diodes, which seem to work fine for my current purposes (medium wave).

Mounted in a pen, the probe makes a pretty effective detector. Connecting the ground wire to the circuit under test is not absolutely essential for approximate measurements, but is probably best connected to get more accuracy especially with smaller amplitude signals.

Note there’s no switch in the circuit, however the current drawn when no RF detected is negligible - a few µAmps, bascially the transistor leakage. Still, it would be a good idea to remove the batteries when not in use.



The Schematic

Breadboard Test

… running on 9V with a green LED and 1kΩ current-limiting resistor R1.

The Build

Pen Build

I switched to 3V supply, a super bright white LED (since the pen handily comes with a semi-transparent green casing) and the current-limiting resistor R1 reduced to 220Ω.

Soldered and ready for assembly..

The Build

The finished product..

The Build

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.