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On Thu, 2007-07-05 at 09:38 -0400, James Knott wrote:
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<FONT COLOR="#000000">Colin McGregor wrote:</FONT>
<FONT COLOR="#000000">> Comes back to my on-going love/hate relationship with</FONT>
<FONT COLOR="#000000">> MythTV (great program but a TOTAL resource PIG!).</FONT>
<FONT COLOR="#000000">> Anyway what I want is an infrared transciever, so the</FONT>
<FONT COLOR="#000000">> MythTV box can both understand an IR remote, and can</FONT>
<FONT COLOR="#000000">> control other IR devices (like cable box, and VCR).</FONT>
<FONT COLOR="#000000">> The receiver part is painless, there are good, easy to</FONT>
<FONT COLOR="#000000">> build IR receivers plans available (I wrote about one</FONT>
<FONT COLOR="#000000">> for linuxjournal.com :-) ), the transmitter is the</FONT>
<FONT COLOR="#000000">> problem. How do you provide power to light the IR LED?</FONT>
<FONT COLOR="#000000">> Well, the conventional answers are:</FONT>
<FONT COLOR="#000000">></FONT>
<FONT COLOR="#000000">> - You don't really, basically you just put in an IR</FONT>
<FONT COLOR="#000000">> LED and a resistor on the serial port. Works, but you</FONT>
<FONT COLOR="#000000">> get an IR transmit range measured in inches.</FONT>
<FONT COLOR="#000000">></FONT>
<FONT COLOR="#000000">> - You connect the transmitter up to a wall tumour</FONT>
<FONT COLOR="#000000">> style transformer and power the IR LED that way.</FONT>
<FONT COLOR="#000000">></FONT>
<FONT COLOR="#000000">> Neither of the above is ideal. Then I ran across a</FONT>
<FONT COLOR="#000000">> design that uses a high capacity capacitor as a</FONT>
<FONT COLOR="#000000">> battery. The serial port is always trickle charging</FONT>
<FONT COLOR="#000000">> the capacitor, and the IR LED gets its power off the</FONT>
<FONT COLOR="#000000">> capacitor. As long as you don't go for high duty</FONT>
<FONT COLOR="#000000">> cycles the IR LED should have a range in tens of feet.</FONT>
<FONT COLOR="#000000">></FONT>
<FONT COLOR="#000000">> So, long range, and just one (serial) cable from PC to</FONT>
<FONT COLOR="#000000">> IR box. Only downside is one pain in the butt part to</FONT>
<FONT COLOR="#000000">> source (plus the previously noted smaller problem of</FONT>
<FONT COLOR="#000000">> looking for a really nice looking way to package the</FONT>
<FONT COLOR="#000000">> final result).</FONT>
<FONT COLOR="#000000">></FONT>
<FONT COLOR="#000000">> </FONT>
<FONT COLOR="#000000">So, why not use a battery?</FONT>
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.... or an array of smaller capacitors in parallel, until you find the right size. This way you can test the design out and tweak it before committing to an expensive part. It's also the kind of thing you can do right now. <BR>
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Batteries would definitely be simpler, though I understand not wanting to keep replacing them.<BR>
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-kms<BR>
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