[mythtv-users] weird problem with IR serial receiver

Richard Woelk richardwoelk at yahoo.ca
Thu Apr 26 04:42:17 UTC 2007



Lord Darkhelmet wrote:
> I built a serial port receiver following the plans on lirc.org (and 
> duplicated all over the place) and it did not work.   After much futzing 
> with it, I got it to finally pick up signals but I had to change the R1 
> pullup resister from 4k7 to 15K.   Based on the number of people who 
> have it working as published I assume something is not right with my 
> attempt.  With the 15k resister in place the supply voltage going to the 
> tsop is 4.97v but the output voltage from tsop is 2.53v and drops under 
> 2 when a button is pressed on the remote.  The motherboard is an old 
> Asus P3V4X and the OS is FC5.  I have not tried either the stock circuit 
> or my version on other hardware yet.   Seems to be working but I'm not 
> sure why or if I'm risking the motherboard.  Any insight would be great.
>
> Dean.
>
>
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>   
Dean,
    You won't be risking your motherboard or serial port with that mod. 
Raising the value of the pull-up resistor will just slow the rise time 
of the digital signal.
Think of the IR signal closing a switch from the output line to ground, 
the pull up resistor allows that line to rise back to 5V
If it works, keep using it that way.

The output of the tsop is a digital square wave with a rate of about 
4Khz, depending on the remote that is sending.
If you can, look at it with an oscilloscope in DC mode. the wave will 
rest at around 5V without a signal, and go to almost zero at the bottom 
of the square wave

HTH

Richard




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