Pls. Help: DIY IR Blaster


New Member
Hi there,

I'm building a PVR, and have come across a problem of switching channels on my FTA receiver. I'd like to use BeyondTV software, which claims to be compatible with Girder as far as IR emitters are concerned. However, I don't feel like spending $$ on an IR receiver/xmitter, since I already have an IR receiver that came with my PVR card.

If I build a simple IR transmitter ( an IR LED in series with a resistor and a diode, connected to DTR & GND of the serial port ), is there a Girder plugin that will handle a simple device like that? I've asked this on Girder forum, but got no replies.

I don't see how such a device could be made to work, because of the tight (and fast) timing requirements of IR signals. The buffered nature of device i/o in Windows makes it impossible to have such precise control over signal timing. I don't think you could even generate the signal envelope with any precision, never mind the carrier frequency...
Please have a look here:

The description is here:

This site
is no longer available, so I only copied the following text from google cache:
To build an IR LED transmitter, use the info at, especially The hard part is really just procuring then correctly orienting the IR LED. The anode (usually longer LED lead) goes to DB9 DTR [pin 4], the cathode (usually shorter LED lead) goes to DB9 GROUND [pin 5]. It does not matter which leg you put the 1Kohm resistor in. The reverse blocking diode (1N4148, 1N914, 1N4001, or equivalent) must be oriented as shown in the picture above, with the cathode (banded end) toward the LED anode. This blocking diode prevents the sensitive IR LED from being reverse biased past its maximum rating (typically 5Vdc). I have run informal distance tests with the above configuration, using a Radio Shack Catalog Number 276-0143 "High Output 5mm Infrared LED" in series with a 1K resistor and a 1N4001 diode. It works to about a meter, but since there are quite a few variables here (e.g. COM port driver current), well "Don't Blame Me" if your setup only goes half a meter. For what I am doing, a meter is sufficient.
Thanks, Treetop! I've already built an LIRC receiver for a friend. He uses that with Girder & Igor plugin, and is vary happy with it. I used SOME of the links you've mentioned. but wasn't familiar with others. In this one:
I'm confused why Marsupial mentions 'the emitter part', his links describe a LIRC receiver...

The only 'Girder-ready' schematic of a receiver/transmitter I've see is the UIRT2:, but this one requires programming a PIC. I was hoping to find something easier than that...

Once again, thanks for your input!
ardo, for what it's worth, here is my experience:

A few years back, I used to drive a IR LED directly from a serial port modem line (I used RTS instead of DTR, but there is no real difference). I used DOS, which allowed me direct control of the port pin. I had to modulate at 40 kHz, which meant toggling the pin every 12.5 microseconds. When the PC was transmitting IR, it could do nothing else.

When I tried to do the same thing on WinNT, I could not directly control the pin. I needed to open the Comm port and toggle RTS through the windows API. Windows could not do it within 12.5 microseconds.

I ended up interfacing to an HC05 microcontroller through the serial port. With it's counter/timer, I was able to transmit and receive much more precise IR than I could ever do on the PC.

(BTW: I did not use a resistor, and instead depended on the current limiting in the RS232 driver. I would not recommend that today).