Re: Connect a wire to an IR receiver?

On 2020-03-28 23:24, Anarky wrote:
> Hello,
> 
> I would like to control multiple devices with my computer. On the
> transmitters page[0] it shows how to use the serial port, so I was
> thinking to build something like this:
> 
> DTR >---(1N4148)---(R)---> device's IR cathode
> 
> 1/ would it work?

You have to be a bit more precise. Most IR controlled consumer 
electronic do not have a "cathode" (an IR diode?) but a demodulating 
chip, TSOPxxx or similar. This removes the modulation from the signal. 
So most likely what you propose would not work. How to eliminate the 
modulation from the sent signal has been discussed here before, for 
example here: 
https://sourceforge.net/p/lirc/mailman/lirc-list/?viewmonth=202003&viewday=20

> 2/ is it dangerous for my PC or my device(s)? I plan to connect 3 on my computer

I would recommend deploying opto couplers, like 4N26, to achieve 
galvanic isolation. Connect the catode of the IR diode (pin 2) to ground 
of the PC, the anode (1) through a resistor (1k?) to the sender signal, 
the emitter (4) to the ground of the receiver, leave base (6) 
unconnected, the collector (5) to where the TSOP was, with a pull-up 
(10k?) to Vcc.

> 3/ how long could the wire be?

Uncritical, in particular if using demodulated signals. Use shielded 
(microphone) or coax cable, just to be safe.

> Thanks.
> 
> [0] https://www.lirc.org/transmitters.html

Be aware that this is a 20 year old document. How many 20 year old IT 
documents are still "valid"? (OK, you asked us, so there is hope for you 
;-)).

Greetz,

Bengt