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LIRC Remote Receiver

So building a serial port based IR receiver for my computer based TV has been one of those projects I've been meaning to do for quite a while. (Think last September) So at the end of March I finally got around to it.

A little background information: basically this gives the computer the ability to receive signals from a regular TV remote. So with the LIRC software it can decode those signals and be configured to do different things, adjust volume, change channel, etc. The basis for the receiver, I got from the LIRC page on serial port receivers.

Here was the result:

I made one slight change from the main schematic on that page. I used a low drop out voltage regulator instead of the one listed. This allowed for use on laptops where the serial port might not output the 10V seen on most desktops. You can see the schematic I used below.

The receivers worked great and all under both Linux and Windows (using WinLIRC on Windows of course). Now here is the kicker: Trying to get it to work under Windows on a laptop natively lacking a serial port. So without doing much research I purchased a USB serial port cable. In my mind it should have worked, but it didn't. Once I had thought about it, I could understand why it wouldn't. The receiver would receive sufficient power but the input signals were all messed up coming into WinLIRC. After doing some research on the net, I came to the realization I wasn't the first person to try this. Then even after much dinking around with driver settings and the receiver circuit, I still could not get it to work.

So taking it to the next step, I thought of using a PCMCIA serial port card. So I borrowed one that was from several years ago. I plugged it and Windows detected a standard COM port on the computer and the receiver worked fine. Being very relieved that I had found my saving grace I ordered a similar card off a site on the Internet.

Finally after getting a working one (the first one I received was defective) I tried it out. The IR software reported no signals coming into it. So after some investigation I found that there was simply no voltage coming out of the serial card. Thus the IR IC had no power and couldn't receive any signals.

After even more fiddling with the PCMCIA serial card, the thought occurred to me that perhaps the lazy people that designed it for some reason designed it only work with self powered devices and not bus powered devices. So I took the 5V being supplied by the USB bus via a USB cable and hooked that into the circuit and it all started working with the PCMCIA card.

So the next step will be to build some sort of DB9 dongle that will provide the required input voltage to the device. I figure this is the best method to get it to work versus permanently re-wiring the device since if it ever becomes unnecessary to use the PCMCIA card, the IR receiver could just be plugged into a standard serial port. Granted this isn't as clean as I had hoped but it will have to do for now.

Posted on: Apr 25, 2006 at 2:37 pm - (0) comments.

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