Kevin Vance - IR Blaster

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01:52 am

IR Blaster

Tuesday, October 27th, 2009
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So when Comcast dropped a bunch of analog channels last month, my mythtv setup got a little less useful. They did unencrypt some digital channels, but I was still down to one tuner for most cable channels.

I got my converter box last week, a Pace DC50X. It works well enough. Even with the RF output, and the digital to analog back to digital conversion, it still looks better than the old analog signal.

Of course, the problem with a converter box is that mythtv can no longer change the channels. The converter comes with an external IR receiver port, a mono mini-jack. So my first thought was to have a sound card generate the electrical signal the IR receiver would make. But there are already established methods for communicating with IR, so I decided to just use an IR blaster.

There are plans for making your own, but I'm not really up for that. My electronics experience is limited to soldering broken connections, and some basic theory from high school physics class. I would not want to plug a circuit I built directly into my PC.

So I bought the serial port one from After actually installing a serial port (heh), it works as expected. MythTV can now change the channels, and I have a pretty good DVR again.

There is one thing that kind of bugs me about it though. When it's transmitting, LIRC masks interrupts. So for the ~1 second it takes to change the channel, the sound skips and the system clock drifts a little. I can probably live with that, but it might gradually drive me insane. I'm not sure which yet.

I'm not too familiar with multicore x86 or linux's IRQ handling, but I wonder if it would be possible to keep the LIRC driver on a different core, and only mask IRQs on that core. Otherwise... I have been looking for an excuse to buy an arduino...
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[User Picture]From: rspeed
2009-10-27 10:55 am (UTC)
Does the box have a Firewire port? Might want to look into that as a way to avoid the extra analog step.
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[User Picture]From: kvance
2009-10-27 02:50 pm (UTC)
Nah, this is the one that comcast gives out for free. It only has ports for coax in, coax out, power, IR receiver, and a switch for whether you'd like channel 3 or 4.

For another $7/mo, I could get a box with a firewire port. But from what I've read, they won't send encrypted channels over the firewire, so it wouldn't be an improvement over my digital tuner anyway.
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[User Picture]From: wikle
2009-10-27 11:34 am (UTC)
If you can somehow incorporate a live animal into the process you can officially call it a Rube Goldberg device.
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From: (Anonymous)
2009-10-30 04:24 am (UTC)
That's the audience ;)

Do cable card enabled tuners cost too much? It sounds like you have 1 in there already and you had another from the first generation you were using on the analog lines?

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[User Picture]From: kvance
2009-10-30 04:36 am (UTC)
As far as I've heard, CableCard will never certify a digital tuner for MythTV, since there has to be DRM all the way to the monitor/speakers. Also as far as I've heard, nobody's done the reverse engineering to make the drivers for them, and you'd have to buy a whole new computer just to get one anyway.

I have 1 digital and 1 analog tuners hooked up right now, the analog one was getting less useful without the DTA box.

Edited at 2009-10-30 04:39 am (UTC)
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