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LED Necklace


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What do you think?

Compare the two schematics and check each connection one by one, you don't have to know anything about electronics to see that the connections on the one you've posted are wrong. I'm not going to go through it and list all the corrections when you're obviously not giving this enough thought.

Why not open my schematic in an image editor, such as MS Paint, and make all the modifications rather than attempting to copy it and potentially introducing more errors?

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Yes, that will work.

The LEDs might be a bit dim with 150R, don't forget that they're only on for half of the time so will appear dimmer than they would if they were connected to a battery via the usual series resistor. Try it with 150R and reduce to 68R, if they're not bright enough.

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You should've asked that before, it should have been your first question.

When there's no signal, the transistor will be off, no current will flow so the LEDs will be off. When the incoming signal is greater than the base threshold (typically 0.6V to 0.7V), the transistor will turn on and connect the cathodes of the LEDs to 0V, forming a complete circuit which will turn them on.

The 22R resistor limits the base current which is needed because the transistor's base looks like a diode which will be destroyed if nothing is there to limit the current. The capacitor blocks DC current and allows AC to pass, some old amplfiers pass a small DC current through the speakers which would cause the LED to light continuously. The diode is required to provide a path to current flowing in the reverse direction, without it, the capacitor will just charge and not discharge, remember the base of the transistor looks like a diode.

Read the Wikipedia article on BJTs.
http://en.wikipedia.org/wiki/BJT

If there's anything you don't understand, please ask.

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I can't get it working. I'm trying the left channel with only one led, trying to start small. Everything seems to be connected correctly. I'll list the components I'm using, maybe one isn't correct. 35v 10uf cap, 2n3904 npn, a 22 ohm resistor, 150 ohm resistor, and a IN4003 diode. Is there any common noob mistakes that I may be making ?

Thank you for your time.

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nevermind, I figured it out, but it is somewhat "blurry". would a peak detector help this ?
Can you reccomend a peak detecting circuit ?
Where would I attach it ?
Also I notice that as I turn the volume up, the leds get brighter.
Is there a way to adjust this so that it would be as bright at listening volume as they are on max volume ?
I plan using a splitter and listening while it blinks.

Thanks for your help

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Would it be possible to use one pot for the whole thing ? It would be easier to make each color the same brightness that way.
Also, would this peak detector work: http://freecircuitdiagram.com/2008/09/07/single-transistor-half-wave-peak-detector-circuit/
Would it be possible to also have 1 peak detector for the whoe thing ?

Thanks for your help

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It doesn't matter whether the pot is before or after the the capacitor.

To alter both channels simultaneously you'll need a dual ganged pot, alternatively you can not bother and mix both channels together by using a 100R resistor for each signal.

That's a clever little circuit but its output impedance is very high and a peak detector is only a small part of the circuit.

I think AG's idea is to use the peak detector to set the threshold for a comparator which switches on the LEDs. The good thing is that is it shouldn't need much adjustment, once set up, it will work over a wide range of volume levels.

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