LED Popping

[HankMcSpank]

Thanks guys....keep 'em coming.

Robert - tried all of those!

Jumper - my PWM pin is in use for other things! (& I want to stay with the PIC I'm using - a 16F690)

Mike - the amp on my circuit is already muted (I didn't explain very well - it's the gain in the guitar amp that is high. The guitar signal feeds into my circuit....which I mute when switching - but this source guitar signal is simply 'Y'ed into my circuit.....the original guitar signal proceeds to the guitar amp as normal - it's this signal that's picking up the LED switching lcick from my circuit.

So the path is like thus....


Guitar pickup 'Y'ed off into two .....
1 ----> into my circuit
2 ----> onwards to the amp as normal (clicking heard on high gain settings from switching in my circuit above)

I need a way of ramping up the led slower so there's no sharp current surge (which is what reckon was causing the pop) - PWM would have been perfect, but like I say, I really want to stick with the 16F690. I have some spare pins left, so it's plausible to do some kind of pseudo PWM.

Toying with the idea of an inductor in series with the led (or possibly bringing a cap into play), just to delay the sharp switch on.

I found this site, but the jury is still out that they've got it wired correctly (I'm pretty sure it's wrong!)...

http://www.muzique.com/lab/led.htm

[rsocor01]

Toying with the idea of an inductor in series with the led (or possibly bringing a cap into play), just to delay the sharp switch on.

A cap in parallel with the LED won't work as the current will rush in to the cap trying to charge it, making matters worse. Now, a resistor in series with an inductor would do just fine. Keep in mind the time constant L/R. One L/R time constant is the time required for the current in an inductor to increase to 63.2 percent of the maximum current. This is similar to the RC time constant in a capacitor+resistor circuit.

By playing with the R and L values, you can adjust the delay that you want for the incomming current. I found this very nice picture on the web that ilustrates this point.



http://www.tpub.com/neets/book2/2d.htm

Robert