In article <20020930224924.74008.qmail@...>
>I'm trying to run LIRC with a home-brew
>Tx and Rx on the same COM port. Has anyone else tried this, and if so,
>how have you got on?
No problem for me.
>From what I can see, when I have both connected, the range/accuracy of
>both drops sharply. On their own, the Rx has a really good range, and
>catches about 95% of commands I beam at it, and the Tx has a fairly
>good range, and again, sends every command I ask.
>When both are connected at once, the Rx reliability drops, and only
>decodes 5-10% of commands, at hardly any range. The Tx range also
>My main question is - is this a function of the current (i.e. if I give
>the Rx it's own external power instead of using the RTS will that
>improve things) or is it a case of the software only being able to
>handle EITHER Rx OR Tx due to its interfacing with the COM port (in
>which case, I assume there's little I can do to fix it).
My guess is your system uses a MAX232 or similar, and it can't handle
the curent draw of both the receiver and transmitter. Try measuring the
voltages under the various conditions. An external power supply is
probably the best solution. A 9v battery can be used for testing.
>Finally, as a bonus question - assuming I ever get over the above
>problem, how possible would it be to hang TWO Rx's across the same
>port, using diodes on the returning data to separate them, and using an
>external power supply for each if needed?
With the extra current draw, you are even more likely to need the external
power. As someone else said, the receivers are open-collector and can
be put in parrallel. (At least one brand has internal pullup resistors.)
One 78L05 can supply more than enough power for several receivers.
Blars Blarson blarson@...
"Text is a way we cheat time." -- Patrick Nielsen Hayden