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Old 27th June 2006, 12:54 PM   #1
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Location: Quebec, Canada
Default IR transmitter woes. Help please.

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.
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Old 27th June 2006, 01:13 PM   #2
AuroraB is offline AuroraB  Norway
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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.
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Old 27th June 2006, 01:20 PM   #3
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Thanks for the response.

Quote:
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 ?
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