Metalab Bypasses IR Remote With Audio Circuit

Infra-red (IR) remotes are great, unless you’re in a hackerspace that’s full of crazy blinking lights and random IR emissions of all kinds. Then, they’re just unreliable. Some smart folks at Metalab in Vienna, Austria cut out the IR middle-man with a couple transistors and some audio software. They call the project HDMI Whisperer, and it’s a cute hack.

Metalab’s AV system has a web-frontend so that nobody ever has to stand up unless they want to. They bought an incredibly cheap 5-to-1 HDMI Switch to switch between displaying multiple video streams. But how to connect the switch to the Raspberry Pi server?

Fortunately, the particular switch has a remote-mounted IR receiver that connects to the main unit through a stereo audio jack. Plugging this sensor into a laptop and running Audacity while pressing the buttons on the remote got them audio files that play the remote’s codes. Simply playing these back out of the Raspberry Pi’s audio out and into the switch’s IR input through a tiny transistor circuit does the trick. Now they have a networked five-way HDMI switch for $10.

Given the low data rates of most IR remotes, we could imagine using the same trick for devices that have built-in IR receivers as well. Simply clip out the IR receiver and solder in a couple wires and then inject your “audio” signal directly.

But IR hacks are loads of fun. We’ve seen a bunch here, from the classic camera shutter-release hack to a more general tutorials on cloning IR signals with Arduinos.

Thanks [overflo] for the tip!

20 thoughts on “Metalab Bypasses IR Remote With Audio Circuit

          1. I dont think that “a cult of pedophiles has been looking at pictures like this for thousands of years” is an argument against the disturbing nature of the image.

        1. I don’t know, but looking at image and seeing a pregnant child is it’s own kind of disturbing. not enough information discern if it female is a child or a petite adult. I giuess people will see what they want to see . Just like those who see and adult with shaved pubic hair and say she looks like prepubescent girl when the remainder of body says adult woman. [shrug] Moving on I was perplex why the image was used until I seen HDMI Whisperer

          1. Did you idiots also happen to see the freaking wings? It’s not a pregnant creature, it’s a little fat cherub angel.

            And seeing you people are so daft you should probably hide under your bed now because you upset your imaginary superguy in the sky.

            noun (plural cherubim)
            1 (plural cherubim or cherubs) an angelic being described in biblical tradition as attending on God, conventionally represented as a chubby child with wings.

    1. They essentially have! Audio isn’t audio til you hear it. It’s just a signal. IR remotes usually use a 36-40KHz modulated IR LED as a carrier wave, sending on-off pulses that are well within the range of a PC sound card.

      Receivers use a 3-pin demodulator IC, it has the photodiode behind a window at the front, and a circuit to demodulate the carrier, sending out just the pulses. You’ve probably seen one if you’ve stared at the display of a hifi or VCR. Presumably the jack carries the 3 pins, power, gnd, and data out.

      So just connect gnd and data out to your sound card, send some pulses in the range of perhaps a few hundred Hz, Bob’s yer uncle! Doesn’t matter if the pulses aren’t exactly square, it’s the timing that matters. In this case the “effort” was a jack plug lead and a bit of messing with Audacity. That’s the easy way.

    1. They are “cutting out the IR middle-man”; the IR reciever plugs into the HDMI switch using a jack plug, and sends the data through that. Rather than plug the IR reciever into the jack socket, they’ve plugged the audio output of the raspberry pi into it, and sent the same data as the IR reciver was sending, but sent as audio clip triggered by a web interface-triggered bit of software. The connection is entirely electrical (until you get into the wider networking side of things); there’s no infra-red used.

  1. When i saw this, i started to think about how could you implement this IoT style.

    An IR-reciever to learn the commands from the remote of your tv.

    An WiFi-bridge to FM or 433Mhz.

    Then every device has a (trans)reciever with IR-Led stuck to the front end.

    You could then create scenes.

    And remotely turn off the tv etc, set timers

    In Theory the reciever could be an IR-reciever with audio-Jack with MIC so your smartphone would record the commands send it to the Hub for further use.

    Or create a predefined command table.

    Just my 2 cents

  2. Pretty cool.

    For a while my company was thinking of using “audio” files so that customers could bootload new firmware with any laptop or smartphone, but that project fizzled out.

  3. I suggested exactly this approach a couple of months back at work to some coworkers for exactly the same use (though with an x86 PC rather than a Pi as the playback device, as it’s already part of the system). Considering they use an audio jack for the IR input, it makes for an easy way to connect everything up ;) Originally we were going to use RS-232 controlled HDMI switches, but those are becoming rarer and more expensive, and we needed something that could do 4K, so this fit the bill. Glad to see someone else managed to get it working too :)
    I’ve also used HDMI-CEC to do it with the Monoprice switch that had that. If there’s not a lot of CEC-capable stuff on the bus, you can get away with something very similar there (just playing back a waveform), but the IR approach is far simpler.

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