IR decoding with your… guitar

[Benjamin] sent in the craziest thing I’ve seen lately. He’s using the magnetic pickup in his electric guitar to sense IR signals. The guitar is hooked to a preamp that’s feeding into his computer. By capturing the pulses with something like audacity, you can grab samples of the codes without building any specialized hardware.

If you’ve got something for Hack-A-Day, use the tips line!

25 thoughts on “IR decoding with your… guitar

  1. If i understood right.. You connect a el guitar to audio-in at your computer (trough amplifier), then you record with audacity (or something), then you just point a TV-remote (or something sending IR-signals) at the guitar strings?

  2. I agree with that #1.

    It’s really weird that IR can disturb coils… does anyone has any idea of the physics involved???

    I wonder if it’s true IR or some side effect, like, say, some waves directly from the remote control circuit, and not from the IR leds on it. I definitely have to try this thing… and I guess I’ll try replace the led by equivalent normal diode to test my first guess, too.

  3. Hey, guess what? I’ve just tryed with my old passive bass and Audacity. It actually works (I mean I get different signals when I press keys on the remote) but it works no matter where I direct the IR beam… the idea is to have the remote close to the coils, and even when hiding the IR or directing it in the opposite direction of the coil, the signal is exactly the same.

  4. This is quite a common occurrence when doing sound for bands – a friend of mine once put his mobile phone next to the ‘line in’ for a 100W amp (turned up to 11) – the interference of him getting a text message, when amplified, caused more than a few people to jump ;-)

    Anyone know any more acoustics hacks? (Has anyone else heard of the mysterious ‘cones’?)

    Sapere Aude


  5. It is *not* recording the infrared light from the controller. It is recording the EMF from the electrical pulses that drive the LED.

    You can put any electronic device near a guitar pickup and hear the EMF. Try a simple electric motor and you’ll get the idea.

  6. From a mobile near a speaker is due to EM waves effecting the magnetic field used to drive the oscillating deeley.

    I would guess this is kind of the same, IR is still EM. This might explain why all the pulse are same width, it’s only the change in the field that produces a change so the fact that one is of longer duration makes no change.

  7. The reason this is so effective is probably because the LED in a remote control is way overdriven with huge current pulses, sometimes as much as an amp rather than the 20mA that an LED is usually rated for. They can get away with this because the pulses are very short and the overall duty cycle keeps the average current within the rating of the LED. I think you’d be unlikely to detect the current pulses if it were switched at only 20mA or so.

  8. I used to do this as a kid, although I used an AM/FM radio. The AM coil antenna inside the radio case will pick up the same EMF from a remote, the remote is basically a very weak RF transmitter as explained above by Dan and Henry.

  9. I used to do stuff like this all the time. Just grab any random electrical thing from around your house and use it right in front of your pickups. I saw Eddie Van Halen use a drill and that got my mind wandering… dunno how/why it works, but you can get some weird sounds out of things. Pickups that aren’t potted correctly can become microphonic, so you can sing into them and get some weird sounds for your vocals!

  10. “So does this mean Eddie Van Halen is now an Uber hacker???”

    No, it probably means that Les Paul was an “over” (German for “over” is “uber”, so it seems) hacker before his time. You could call him a “großhavker” which would imply he was a “mega hacker”, or a “Superhacker”, which translates to English as “super hacker”. It’s up to you, but for the love of the German language, please stop abusing “over”!!!

    -he who stacks pork

  11. Well time to do research- is it the current going through the LED? In that case desoldering it should cause the interference to stop.
    To me it looks more like emf from some integrated circuit triggering the modulation since we see spikes instead of either the 40kHz carrier or a signal for the whole duration of each bit.

  12. It would be interesting to see what range of signal the pickups actually pick up. Obviously sound within the human range is caught, and Garry Goodman has an 11-string bass whose pickups can detect the 17hz of its lowest string. I may not be fluent in the exact physics, but I have a moderate understanding of the forces involved. Could lightwaves, microwaves, etc. be picked up as well, with the proper delivery?
    From a musical perspective (I play the electric bass), this is facinating to me. I’d be keen on investigating this further.

    Info on Garry Goodman:

  13. I don’t think this is capacitive coupling, but it’s a nice try. Capacitive coupling involves a build-up of charge on one plate; this can’t occur here because there isn’t a pickup ‘plate’ – if the coil were to act as a pickup plate, both leads would have the same charge, yielding no change in voltage (that requires a difference in charges).
    I think it is more likely that the change in magnetic flux is generating the waveforms here. This is because there is a high current in the remote, yielding a relatively strong magnetic field. The voltage generated in the pickup is given by the equation CHANGE IN MAGNETIC FLUX / CHANGE IN TIME = VOLTAGE. When the remote’s circuit turns on the LED, the magnetic field increases, causing a positive change in flux on the pickup. When the remote’s circuit turns the LED off, the magnetic field decreases, causing a negative change in flux.
    By the equation above, voltage is directly proportional to the change in flux, so this explains the spiked waveforms above and below the 0 line (when the current is held at the same level, there is no change in flux, so there is no voltage).

  14. #18

    It could indeed be capacitative (though I suspect the inductive coupling as you do). The capacitor would be formed between the pickup and the remote circuitry, with the air between as the dielectric. A charge appears on the remote side, and is coupled to the pickup coil. I believe this is the same effect behind radio transmitters and antennas.

  15. re: 18

    i admit i don’t know much about radio transmission, so you could be right. luckily, there is a simple way to test which effect is making the waveform. someone could move an electrically charged balloon over the pickups. if a change in voltage is detected, the effect we’re seeing is not due to magnetic fields but to capacitive inductance.

  16. I record vocals for my band by putting a cell phone next to the pick ups, then calling the phone and singing into the phone I called it from. You get some pretty interestign sounding vocals.

  17. I actually noticed this a while back. I kinda made my own hack by hitting record into my Sound Forge program, and then I noticed that I could hear a slightly airy high frequency. It was my palm pilot cell phone battery. It was emitting an almost scary frequency so I wanted to record it. You can hear once in a while the “clicks” are the actual electromagnetic pulses, and the frequency is the EMF and RF radiation waves… Kinda makes ya think about sticking it close to your ear again huh? :P I’m putting some links on it cuz well, anyone can use these files. If ya like it, have fun with it.
    The song can be previewed on reverbnation at and listening to the feedback trick track on there. The mp3 of the file can be found here at Rapidshare:

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