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#1
I downloaded Irreco to play around with, but I don't have an HTPC or anything that I can remote control over wifi. I've heard of people making IR tranceivers that plug into a headphone/mic jack (albeit through an op-amp, or similar). Would something like that be possible for the N810 with the current code in LIRC/Irreco? I could probably work out the hardware myself, but I don't know enough about those software packages to start hacking at them, if it takes more than a bit of compile-fu.
 

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#2
I looked into this approach a while back and came to the conclusion that it really wasn't worth the effort. On the hardware side of things due to the power levels you're dealing with the IR performance really won't be all that great (depending on the hardware you mockup your distance/range can be up to a few feet, assuming all is perfect), but the software side of things is more complex as you have to actually cheat and produce sound waves that mix both channels in order to generate the appropriate signal. So that is, it's not as easy as just "Recording" and IR signal and playing it back, you have to specifically generate the signals to match with the audio output capabilities of the tablet's sound hardware; I'll have to look into it again now that I have some time available, but last time I asked about this I got no response from anyone on the software side of things...

Thanks,
-Rob
 

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#3
Originally Posted by jolouis View Post
I looked into this approach a while back and came to the conclusion that it really wasn't worth the effort. On the hardware side of things due to the power levels you're dealing with the IR performance really won't be all that great (depending on the hardware you mockup your distance/range can be up to a few feet, assuming all is perfect), but the software side of things is more complex as you have to actually cheat and produce sound waves that mix both channels in order to generate the appropriate signal. So that is, it's not as easy as just "Recording" and IR signal and playing it back, you have to specifically generate the signals to match with the audio output capabilities of the tablet's sound hardware; I'll have to look into it again now that I have some time available, but last time I asked about this I got no response from anyone on the software side of things...

Thanks,
-Rob
I'm not sure what's needed to integrate with LIRC/irreco, but the signal generation shouldn't be too hard at all. And I'm (perhaps wrongly) a bit more optimistic on potential ranges, but I'm just guessing.

Honestly, though, since the only IR-controllable device I have is my tablet PC, I have no real interest in the software side of this project, so I'm not going to do anything about it. But if anyone does dig into it, and needs ideas on the actual signal-generation side, I'm willing to discuss it.
 

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#4
@jolouis: I hadn't thought about that... As I said, I just vaguely remembered hearing about such a thing being done on some platform, somewhere, at some point, and figured that if it was feasible, LIRC might already have a driver. When I get a chance, I'll start a thread on an electronics forum I participate in, and post a link here (and vice-versa). It would be nice to get something working - the N810 would make a pretty awesome universal remote control.
Also (just thought of it), would it be possible to use a USB-RS232 converter (say, some FTDI chip), and make a USB dongle with a battery for the transmitter? I don't have access to some of the equipment at university that I'd need to build it properly, but if that would work, I could likely put together something good enough for testing purposes. Let me know...
 

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#5
The USB-rs232 converter option can work, but to be successful there are a few things to consider: first, you need to make sure that whatever chip you're using (FTDI, PL2303, etc) supports all the extra signals that you might need for your hardware. For example the simple IR blaster I use on my mythbox at the house is just an IR-LED connected to the DTR line of a serial port (with a diode and maybe a resistor, I'd have to double check now I built it a while ago), and the LIRC serial module just turns that DTR line on and off at the appropriate rate, so for the tablet using a similar approach would require a chipset that will give you proper DTR control. I believe the FTDI and PL2303 will, but never really tried so you'd have to double check.
The second problem for the direct serial version like I just mentioned is that the range is very small; on a regular PC you'll get maybe a foot or two tops, and that's relying on the 12V signal line to drive the LED; on the USB converter the signal lines are usually only 5-6V (depending on the converter, some actually do put out 12V but most don't) which gives even lower performance. Now, there are better circuits out there, but I haven't tried 'em... the biggest issue though is that in order to attach the USB/serial converter you've got to have the kickstand down so you can get to the USB port, which is not always very convenient.
If I get some time I'll try taking a crack at building the IR blaster for the headphone jack and looking into that again too...

I managed to find a reference to the old Griffin Technology product (they discontinued it about 2-3 years ago now, but the patent does a decent job of describing how the thing worked):
http://www.freepatentsonline.com/6931231.html
As long as they don't decide to try and sue us or anything ;-) I know there's a better document around describing how to actually generate the waveforms and things that I'll post up a bit later (I've got it bookmarked on my PC at home but don't have access to it right now).

Last edited by jolouis; 2009-01-08 at 16:47.
 

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#6
Jolouis:
That's what I was thinking of, and it doesn't look terribly complicated. Also, a design such as that would work nicely with the N810's layout, as one could easily take a right-angle phono plug and fabricate/kludge a covering for it and the LEDs that wouldn't get in the way. I'll take a better look at that patent in a little while. I'm not up to the software side of things, but I could definitely build and test the actual hardware; I should have everything needed on hand. *checks parts bin*
 

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#7
Well I've got the right-angle solderable headphone jack connectors that I use for the Speaker/Microphone adapters here, so it wouldn't be difficult at all to get two IR leds and try and cram them all inside it. The software side of things could be a little trickier, especially figuring out how to make it work with irreco AND provide some mechanism to let you choose your remote codes/etc, but for testing purposes I came across another post somewhere about a guy who'd managed to use SOX to generate the required audio signals from a linux command line for a known LIRC settings file, so that sounds like a step in the right direction... unfortunately at the moment I don't have a lot of free time to play with this as I'm going on vacation in about a week, but...
 

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#8
I was just about to post this thread myself, and, happily, the forum does the search for me. :-)

I too am interested in this topic, but like most people, hadn't done the math about available power at the headset jack vs efficiency of IR LEDs.

It *sounds* as if someone upthread did, but they didn't show their work, so I'm still not sure.

For a little more space, I would assume you could build a squeeze-on dongle with a 2016 coin battery and an SMC driver transistor to bump up the power from the headset jack, I suppose, though we're getting into 'fabrication' territory.

What was that "you come up with an open-design widget and we'll build it for you" website/company mentioned on Slashdot last week?
 

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