How do jack infrared adapters work? - Page 1
Forum section: electronics / projects

author: VinzC
author_rank: Frequent Contributor
timestamp: June 19, 2017, 03:23:31 pm
content: A friend and I have foundinfrared adapters on (what appears to be) an audio jackthat can be used as a universal IR remote with an iPhone or an Android phone. First off there seems to be legions of such devices for iThings but for finding one for Android phones/tablets appears not so straightforward a job. I expect Apple and their proprietary policies to use standard connectors and outputs in a non standard way — i.e. I could expect Apple to provide some form shadow power supply through the audio jack but I'm not aware of Android phones to do the same. On the other hand I know that on PC hardware the Intel HD Audio chip is able to make the difference between headphones and a line input because (based on impedance, I guess) so I expect this is also true on a mobile device.But to my knowledge an infrared diode requires a minimum DC level that is way beyond what would be noticeable on an audio jack to me. So I cannot imagine hooking up an IR diode on an audio jack and there you go (more or less)... However my knowledge is not universal and there are still many things I don't know.So my question is: how are such infrared adapters supposed to work on an audio jack?Can such a product be just a scam?Thanks in advance.

author: Zero999
author_rank: Super Contributor
timestamp: June 19, 2017, 03:49:39 pm
content: I suppose it might be theoretically possible by bridging the output and using a voltage doubler but it seems like a scam to me. As you've said, the voltage on a headset jack isn't high enough to drive an IR LED and there certainly isn't enough power. Another thing is I doubt the sound chip will be able to generate the 38kHz waveform most commonly used for IR remote control systems.

author: nuno
author_rank: Frequent Contributor
timestamp: June 19, 2017, 04:00:31 pm
content: I know of irdroid (http://www.irdroid.com/) but it's powered externally. (schematics under Documentation -> Downloads)

author: tszaboo
author_rank: Super Contributor
timestamp: June 19, 2017, 04:11:19 pm
content: The jack output is something like 25mW / channel, working into 16-600 Ohm output. You need something like 1.5V for an IR LED. If you place it between the channels, then it is 0.75V, quite duable, considering the power supply of the amp is something like 3.6V.The outputs are AC coupled, so there is no need for voltage doubling magic.

author: Zero999
author_rank: Super Contributor
timestamp: June 19, 2017, 06:47:54 pm
content: Quote from: NANDBlog on June 19, 2017, 04:11:19 pmA diode in reverse parallel with the LED would form a half wave voltage doubler, similar to what's used to drive a magnetron in a microwave.The question is whether the audio system will have sufficient bandwidth for a remote control application.

author: Cerebus
author_rank: Super Contributor
timestamp: June 19, 2017, 07:29:50 pm
content: People seem to be forgetting that smartphone jacks have a microphone input as well as the outputs, and that input carries a DC bias voltage for the typical JFET impedance converter that goes hand in hand with an electret condenser microphone capsule. Typically 2-5V via a few kohms.

author: Zero999
author_rank: Super Contributor
timestamp: June 19, 2017, 07:33:41 pm
content: Quote from: Cerebus on June 19, 2017, 07:29:50 pmBut the current is tiny, typically under 1mA, far below what an IR remote uses.

author: Richard Crowley
author_rank: Super Contributor
timestamp: June 19, 2017, 07:55:54 pm
content: The description claims that it uses a "supercapacitor" so it could be using the very tiny "plug-in power" from the microphone circuit to build up the necessary power to blast an intermittent IR signal. HOWEVER, the photo shows only a TRS plug, and not a TRRS plug that would be required to tap into the microphone power. It also claims to be "self-powered" but there is no evidence of where one would put even the most microscopic battery or cell in that thing.It claims to use some sort software/app. But never mentions what it is called so one could find it in the App Store (or whatever it is called?)It has the appearance of a complete scam to me. It might be very advanced technology, but then why are we seeing it on Ebay for €4?

author: mikerj
author_rank: Super Contributor
timestamp: June 19, 2017, 08:50:48 pm
content: Quote from: VinzC on June 19, 2017, 03:23:31 pmI can only see Apple and iOS mentioned in the advert, where does it say Android?

author: xani
author_rank: Frequent Contributor
timestamp: June 19, 2017, 09:33:47 pm
content: Probably thishttp://www.freepatentsonline.com/6931231.pdf

author: Zero999
author_rank: Super Contributor
timestamp: June 20, 2017, 07:36:24 am
content: Quote from: xani on June 19, 2017, 09:33:47 pmOh I see they use two LEDs connected back-to-back which doubles the frequency of the pulses. It should work but how well is another matter.

author: Codebird
author_rank: Regular Contributor
timestamp: June 20, 2017, 07:42:40 am
content: I can tell you that these can work, because I used one years ago in an old iPaq. But it wouldn't work in another model of iPaq, which tells me that it is very fussy about the drive circuitry - probably demands a lot more current than headphones, so not all devices can handle it, and I suspect the software may be doing something more low-level and device-specific than just playing audio. Which would explain why they are not available for android devices, which have a great deal of variation in hardware.

author: VinzC
author_rank: Frequent Contributor
timestamp: June 20, 2017, 12:28:57 pm
content: Thank you guys, it feels reassuring to see my deduction wasn't totally off. Nice trick they did in the patent so it even seems doable at home. But again that suggests it most probably wouldn't work with Android devices for the reasons exposed. I also guess this "trick" totally rules out some form of detection on the software side, which can only drive the audio output blindly, right?

author: Jeroen3
author_rank: Super Contributor
timestamp: June 20, 2017, 01:25:43 pm
content: Apples jack plug has ground on a different ring than most androids.https://en.wikipedia.org/wiki/Phone_connector_(audio)#TRRS_standardsApple solved this discrepancy by entirely removing the socket.