Syringe logic probe

[Travis] sent in his oh so simple(why didn’t I think of that) syringe logic probe. that he put together for his version of the sump logic analyzer. Real probes tend to be pretty expensive. With some effort, you can probably fit an led/diode/resistor in there and make a simple 5v logic probe. If you’d like a nice logic analyzer, Spartan-3 board that it’s based on is only $99.


  1. Gordon Rogers says:

    Another really nice logic probe that i have build from kit form in this one: Very small and seems to work very well.

  2. monster says:

    i’m torn between making a joke about downloading a virus like hepatitis from reusing the logic probe and making a joke about being able to use heroin while hacking

  3. dax says:

    jeez, with any sort of fumbling — I’d want to dull down the tip a little. Just a quickie on a bench grinder or something.

  4. blarg says:

    Yeah, I was thinking about a heroin joke as well. Certainly would raise eyebrows. Think the germs would be killed by the electricity?

  5. J Pino says:

    eeeew…. I dunno… A syringe… hummmm…

    I do prefer tu keep using this logic probe with pulse injector:

  6. BigD145 says:

    A syringe can be had for free from a needle exchange, which makes this quite cheap.

  7. Brent says:

    For you kids out there, this is an old idea and was pretty common back in the day that logic probes were a more common piece of test equipment. I remember seeing it in an electronics magazine nearly 30 years ago.

  8. Mike says:

    Can you imagine what a cop would think if he had this syringe probe on the seat of his car when he got pulled over? That would make a good segment for the show cops.

  9. mike says:

    if I was more awake I’d make a joke about track marks/PCB tracks.

    Actually, my concern is with the needle being stainless steel, which isn’t a very good conductor. I wonder if there are any alloys that will “stick” to stainless but enhance its conductivity ? A better idea might be to get that ultra-tiny kynar wire, and run it *inside* the needle, and have a tiny exposed lead coming out, maybe coat the stainless neeedle with a non-conductive film.

    If kynar wire didn’t work, just unwrap some braided wire and use one braid, although that may conduct with the steel tube and mess up the signal. I would highly advise putting it back in a box when you’re done, if you forget and drop that in your toolbox or on your floor, Murphy will assure you find it in the most painful way possible.

  10. Dan says:

    Buried as lame. Wire wrap wire or a household pin work just as well, if not better, and are less dangerous.

    This guy is a hack anyway.

  11. atrain says:

    Buried? Where do you think you are?

    Dan: A household pin doesn’t have the precision of a needle. In some cases, when working w/DIP stuff, you can just use a paper clip. This is good for when you are working on a very small scale circuit.

  12. Dosbomber says:

    At last! Something geeky to put my old unused insulin syringes to use!

  13. andre says:

    Pretty neat. I wonder if you could make an array of these things with variable spacing for a logic analyser.

    Polymorph this might actually work well for extracting data from broken PCB’s you might run into, and reflashing “dead” PC motherboards.

    Now, the really clever bit would be to incorporate a talking frequency/waveform analyser into said syringe :)


  14. RM says:

    Can anyone tell me how I could use a logic probe to test laptop motherboards? I would like to use a logic probe to test mosfets, voltage regulators and controllers like maxim/isl chipsets.

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