Is it possible to drive a tip31 from the signal generated from an mp3 player? Answered
I have been reading through the many many instructables about driving leds from an audio signal, but so far my experiments have not worked out. I'm trying to drive one led from the audio signal coming from a pair of earbud style headphones.
Here are some videos demonstrating the circuit.
(I can't get the editor to embed videos today, so please follow the links to view the youtube videos
Proof that the led works
Proof that the transistor works
Hooking up the audio signal - I got nothin
Proof that there is an audio signal coming into the circuit
I'm basing this circuit on the numerous diagrams on instructables for syncing an led to music. Here are just a couple of them...
Sync LED to music
LED Music Sync Headphones
These and many other instructables show the same circuit and they all seem to be working, so what am I doing wrong?
I hooked the base of the transistor up to the signal coming from one half of a earbud type headphone wire, hooked the ground of said wire to the emitter, and then hooked up the collector/emitter to a circuit with one standard led and 3V worth of batteries.
I checked the output of the headphone wire with an oscilloscope, and there is definitely audio coming out of it, but it's a very tiny signal, on the order of a few millivolts. How does such a small audio signal generate enough sound to be heard? How does anybody drive a transistor off such a tiny signal? Doesn't it need at leat 0.7 volts to get over the diodey hump of the base-emitter junction. ( I don't know, that was a pidooma, it's been way too long since my last electronics class. )
thanks for any thoughts...