is this circuit correct?

Question

Parts Needed:
1 x 9V Battery
1 x Standard 3.5mm Male Plug (if plugging into a headphone jack like me)
1 x 100K Resistor 1/4W
1 x 22K Resistor 1/4W
1 x 470 Resistor 1/4W
1 x LED (or 2)
2 x General Purpose NPN Transistors (BC547 in my case. I had them lying around)

Below is the schematic with the input coming from one of the channels given by the 3.5mm plug:


http://www.runtimeerror.net/blinky/index.html



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Answer 1

Yeah, looks fine to me. If you wanted, you could replace the 22k with a 50k pot, enabling control over the bias point, and/or a 1 or 5k pot in series with the input before the divider to give a bit of gain adjustment.

This reminds me of something I put together a few years ago. I had a 20-amp solid-state relay and wired it pretty similiarly to your circuit. I fed it from a .wav of thunder loop, which also fed my beefy stereo, and plugged in a 500W halogen worklight and a xenon stobe from Radio Shack. Every Halloween I set this up to illuminate a gallows with the skeleton of a pirate hanging from it. Thunder and lightnig, everybody loves it.

Answer 2

Both Gary and The Wiz seem to have the right idea. I would try replacing the 22k resistor with a 50k - 100k pot, but also add an electrolytic capacitor of 1 -10uF from the input signal to the base af the transistor. It is possible the sound card output has a low resistance which is draining off the bias being applied to the darlington pair, causing it to lose sensitivity to low level signals. Be shure to connect the + side of the cap to the base, and adjust the pot for desired effect. Good luck!

Answer 3

Hi! I went to the schematic and found it straight forward. Looks like it ought to work fine. If you discover you must turn up the music very loud before the LED lights you can adjust the bias on the input transistor's base. Try raising the value of the 22k resistor to increase the circuit's sensitivity. If the LED lights with no input signal present, try lowering the 22k resistor. Have fun...........................

Answer 4

You could probably get away with just using 1 transistor. That double arrangement is for higher power loads, say like a DC motor. An LED shouldn't need that much current.