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Wiring 2 Red LED's Into IR Amplifier

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Wiring 2 Red LED's Into IR Amplifier

Postby GazzaS » Thu Jun 23, 2011 12:18 pm


I hope someone can help.

I originally took an IR Amplifier circuit that takes a 5v IR signal (from IR extender or USB-UIRT) and amplifies the low power emitter into a high power room blaster. The circuit is here:


I modified the circuit to give me 3 IR LED's in parallel so that my entire room is covered (these are high powered LEDs with 1.2v forward voltage and 100ma forward current), reduced the 15 ohm resistor to 10 ohms and am powering it with a 9v battery instead of the 12v source. I am also using L940-36V IR's and an MPSA13 transistor.

This circuit works perfectly, however I now want to modify it to add a Red LED at the blaster area and another at the power source area with the goal of allowing me to see when an IR signal is emitted. I added one forward voltage 2v Red LEDs in parallel to the other three IR LED's with 400k resistor and the other one in parallel to the circuit with another 400k resistor. However they do not seem to light at all. The circuit tests fine and connecting power to the LED's lights them up, but in the circuit they just will not light up :(

I've very new to electronics (as you can probably tell) so am probably doing something very silly. Any guidance is most welcome.


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Postby loupurdie » Sat Jun 25, 2011 4:44 am

You can also use Google.com to find many tutorials, tutoring and free information...for example you can find many online forums for electronics...they can give good information and advice on how to learn electronics.
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Postby GazzaS » Sat Jun 25, 2011 7:49 am

Thanks for the reply.

I have looked at a lot of tutorials and information and was posting on this forum after I still could not work out why the LEDs in parallel would not work. Isn't that why this forum section was created?

Anyway worked out that because the IR LED's were 2v forward and the red LED was 1.2V it would not work in parellel. Therefore I moved just one red LED into series and worked out the resisitor required based on the 9v - 1.2v - 1.4v (transistor). Now works pefectly and gives me a visual indication when IR signal is sent.

My only query now is that when the device is unplugged from the IR emitter port I see sometimes the RED LED lights very dim when the emitter lead is moved. Any ideas why? It's like it's like the NPN tranistor is picking up just enough voltage to let some current through.


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