maybe too simple?
Hi,
From the looks of those pics, these guys have made all the points I was going to make....simply connecting up an audio source to the base of a transisitor used to switch LED's may in fact work, but its a very crude way of doing things.
Audio source may blow your transistor...or not provide enough voltage for it (0.6 usually). And connecting LED's without any form of current limiting resistor will make em heat up, if not blow instantly (depending on your power source). LED's also have a voltage requirement...if you've got 3 1.8V LED in series...you need at least 3*1.8 = 5.4V to get them to light up.
Also, it leaves no room for improvements..like having a different colour LED for bass, middle and treble.
It might be a good idea to use a single stage opamp, setup as a comparator (or..a comparator for that matter
) that way you could add a potentiometer to adjust the 'sensitivity' so that your LED's flash nicely in time with the music. I would also add a diode on the input, along with a zener diode to protect your circuit against massive signal peaks (10v+).
Try google for 'clipping detector'. Its a circuit used to indicate when a signal input is too large, and needs attenuating. It turns on an LED when the input goes over a certain level (user adjustable). I think it does exactly what you are after.
An alternative, but still, very simple solution would be using logic...like a 74HC04 inverter or two. These inverters are quite handy for simple switching solutions and theres plenty of schematics on the net, using feedback resistors to change the sensitivity, add hysteresis. BOTH of the above solutions would probably need a power transistor for driving the LED's. It might not be necessary for a few LED's, but it'll allow you to connect more in the future, or higher current (brighter) LED's.
Its all about how simple, or complicated you would like to make it. Obviously simple is better (and cheaper) but I wouldn't go too simple or you'll be facing reliability issues.
My two pence.
Blueteeth.