IR transmitter woes. Help please.

[argofanatic]

Hi all,

I'm working on building myself a super-duper, browser based, touchscreen remote control for my audio-visual setup. So far I have everything working including the learning remote portion.

I'm using winlirc (the windoze version of LIRC . The IR transmitter that I built is giving me a lot of grief. The schematic I'm using is here .

The transistors that I'm using are a BD139 and a BD140, the IR diodes are LTE-5208. The diodes are IN4007's.

Here's my problem, the circuit only works if I place my finger accross the silicon diodes and the PNP transistor's emitter! (Not quite sure how I discovered that). Also my range is only about 3 feet.

Any help in getting this working would be very much appreciated. An alternate circuit for driving the IR leds can also be suggested. My plan is to have 8 IR leds in an octagonal arrangement (illuminate every part of the room, because I have equipment scattered everywhere).

Thanks,
argo.

[AuroraB]

Concidering that you are "stealing" power from the DTR line, both your transistors and the diodes seems very high power- BD 130/140 having low hfe for the job.
Something like 2N3904/3906 or BC546/550 ( or any small signal type) and 1N4148 is better suited for the job.

[argofanatic]

Thanks for the response.

Originally posted by AuroraB
Concidering that you are "stealing" power from the DTR line, both your transistors and the diodes seems very high power

Those parts are what I had kicking around the parts drawer. If I were to supply 12V directly rather than "steal" power, would this be better ? Or would part substitutions still be in order ?