I am searching for a method to detect the type of metal of something solid and small and thin. The test surface is approx 4x2 cm with a thickness of maybe a few millimeter.

I cannot use magnets in this specific case but I can make direct contact with the surface (using a robot arm or another method) so I thought about using something like electrical conductivity (in uS/cm). I am not even sure if that's possible but according to this https://www.tibtech.com/conductivite.php?lang=en_US there is a big difference between the two possible materials I will face either steel (10,1) or aluminium (36,9).

So I am searching for hardware preferably a digital sensor that can do this using my raspberry pi. Something like an electronic conductivity sensor for solid materials as I only seem to find sensors for use with liquid. Does anyone know of such sensors or another method I can use other then electrical conductivity or magnetism to determine the difference between aluminium and steel.

I also thought of using heat and time measuring the heat conductivity but it has to be low heat as plastic is connected to the metal. Or using an (ultra) high definition camera with proper light and trying to determine it based on color difference. Which seems hard to do and unreliable due to other factors.

Also, if you know of any projects where they do use methods or another metal type detection technique with a raspberry pie, just for educational purposes, please share. As I couldn't find anything actually.

Edit: I found this (https://www.youtube.com/watch?v=B0lrcvT2HRc) again for liquids, but I will experiment to try to make a variant on this. But still, any ideas are welcome.

  • Your question is interesting, but I feel that it may be off-topic for Raspberry Pi SE. As a suggestion, you might try posting it on Physics SE. If you do, please delete your question here as cross-posting is "discouraged".
    – Seamus
    Jan 2 at 21:06
  • your question has nothing to do with Raspberry Pi ... asking how to interface a specific sensor would be on topic ... asking how to design a sensor is not on topic .... you are doing yourself a great dis-service by asking here ... it is like asking how to overhaul a lawnmower motor at a gardening forum
    – jsotola
    Jan 3 at 1:10
  • spectrometer can get you down pretty close to the alloy of steel... be ready to drop tens of thousands of dollars. some handheld ones even have external interfacing capabilities that could talk to a pi.
    – Abel
    Jan 3 at 14:28

1 Answer 1


The simplest of-the-shelf device to do this would probably be a low-resistance meter, using 4-terminal sensing. You could probably create your own version, but the design would be quite tricky, as the actual resistance value will be really low.

Would it be cheating to use the metal plate as a core in an inductor? I'd guess that your materials show very different characteristics when placed in a coil. I know that an inductor works by magnetism, but you say that you can't use 'magnets', and this method doesn't.

Failing that, what about weighing with a load cell? If the size is variable, it'd be quite easy to measure it with a camera and OpenCV, and work out the material from the density.

  • downvoted your answer because it is off topic to answer off topic questions ... your answer has no Raspberry Pi content
    – jsotola
    Jan 3 at 1:12

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