Buffering a Self Flashing LED in a pedal. (solved)

[Rylan]

I just made a boost pedal and the person it's for wanted a blinking LED, I used a self flashing LED with an inline resistor but noticed a background pop or click type noise with the flashing of the LED. I was thinking a polarized capacitor might help but didn't have a good starting point to try for a value, was going to just stick a 10uf in there and see what happened unless anyone has any expertise on this.

[daverdave]

Have you a copy of the schematic and the location of the LED you're sticking in there? A datasheet for the LED might help as well.

I've not got alot of experience with flashing LEDs but it sounds like an issue with it switching a fairly large current as it turns on and off, this might be causing an audiable click due to the transient. Using a decoupling cap is going to create a time constant with the series resistor which I imagine would slow down the speed at which the LED become illuminated fully due to the charging and discharging of the capacitor.

[Rylan]

Thanks for the reply, I actually have it working.
I tried some capacitors this morning and found the value of 16v 470uF across the LED to buffer the current sufficiently to remove all audiable click/pop and has no effect on the speed or intensity of the LED, nor does it impact the sound.
For anyone wondering it was a biasing mosfet type boost, like the zvex stuff.

[Rylan]

Oh by the way, if anyone ever does this, a build note:
Wire the capacitor from the middle leg of your footswitch to ground, that way when the pedal is off the capacitor is disengaged. Otherwise the LED will have to blink away for about 30 to 60 seconds while it discharges the capacitor.

[nd_efx]

You can use even much smaller cap like 22uf with serial diode in font of it ( like RC filter but diode instead of resistor ). When used with regular diode this is simple way to achive soft light on/off.

[Rylan]

Ah nice tip, I had considered trying some diodes but thought since the LED itself is a diode that it might not work so well. I'll try that next time as I would rather avoid storing 470uF all the time, I imagine your method would be more battery friendly than mine.