[mythtv-users] IR blaster problems

Alen Edwards allen.edwards at oldpaloalto.com
Thu Jun 26 16:14:14 UTC 2008

Tony Brummett wrote:
> On 6/23/08, Ray Whiteman <ray.whiteman at consultant.com> wrote:
>>  One thing I would point out is that I don't need to perform
>>  set_transmitters...... Not sure if this makes any difference. The only
>>  other question I have is, do you have the correct lirc device? Are there
>>  more than one by any chance?
> There's only lirc device, and since the receiver part works fine, that
> can't be the problem... unless the transmitter part needs a separate
> device node?
> Anyway, I've come to a solution, though it's a bit on the ugly side.
> I ended up building a serial port blaster, and it worked... kinda.
> The STB would see most of the button press events I'd send, but for a
> 3-digit channel change, that meant success was well under 50%.
> I ended up disconnecting the IR emitter from the serial port blaster,
> and connecting the wires where it used to be directly to the leads of
> the IR detector in the STB.  Now it's worked 100% of the times I've
> tried.  I was just wondering, if anyone happens to know, if it would
> be a good idea to put a resistor or diode somewhere in the line to
> prevent an overvoltage problem?
> -- Tony  brummett at gmail.com

In all likelihood, you would have killed it already if it was a 
problem.  Ideally you would make your setup place the same voltage on 
the sensor as you would get from shining a remote control on it.  I did 
a quick search on ir detectors and see that their output can be anything 
from a resistance change, to a small signal level, to a TTL output.  You 
would need to know what you are dealing with.  Bottom line is I would 
definitely use a resistor to limit the current and try and put the same 
signal level there as is normal.  btw, if it is a TTL output, it is 
possible that using the remote could blow out your blaster circuit.  It 
is also possible that you could add two diodes, one on the stb emitter 
and one from the blaster to prevent either from blowing out the other.  
It really depends on what the stb circuit is.  Disclaimer: I give this 
response as a circuit designer, not as someone who knows specifically 
what is in your stb.


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