Fade On LED Gimmick

[genXslacker]

I'm a nostalgia-hound and typically prefer classic features. But I guess* ADHD is in my basket of neuroses, and I'm highly entertained by a pedal gimmick even if I'd never use it on a second pedal. Also, I'm away from home and the rest of you have to suffer because I can't get into my sweltering garage shop and make some pedals that I'm probably going to be disappointed with.

Anyway, if the title of the post isn't obvious, these little boards fade the status LED on and off, instead of the usual instant-on-or-off we're all used to (and very satisfied with and don't think require any improvement).

The first is a mostly "by the rules" vero layout. The second allows one to save a relatively large amount of space for those crowded builds that require a gimmick. Both are attributable to the MadBean SSABP 3PDT cheater board.









A few notes on the compact version:

Piggyback the diode on the 1M resistor in parallel.

The electrolytics are going to be leaning away from each other quite a lot.

Point-to-point solder the power wires onto the 22k resistor leads.


*translation: "I know"

 

[SpringReverbFan1234]

Nice layout, should be quite cheap and easy for a power indicator.
Normally I just use the "Millenium 2" bypass from http://www.geofex.com/article_folders/millenium/millen.htm
I made boards for it here: https://oshpark.com/shared_projects/icrDmvuG

 

[phi1]

Nice! Could it be simpler, like just a big cap in parallel with the LED?

Ok maybe it’d have to be too high capacitance to get a slow fade

 

[genXslacker]

Nice layout, should be quite cheap and easy for a power indicator.
Normally I just use the "Millenium 2" bypass from http://www.geofex.com/article_folders/millenium/millen.htm
I made boards for it here: https://oshpark.com/shared_projects/icrDmvuG

Nice!

 

[genXslacker]

Nice! Could it be simpler, like just a big cap in parallel with the LED?

Ok maybe it’d have to be too high capacitance to get a slow fade

That's above my pay-grade. I'm just good at following instructions, but the logic makes sense to me.

 

[Feral Feline]

You got a schematic for that?





YEAH... WELL...

P E R F !​

I had drawn up several perf layouts of varying compactness, what you see above is my first (11x4) and last (6x5).

[EDIT!]
Found errors in the resistors, fixed those and re-uploaded; also re-jigged 6x5 caps to face the same way (Robert's influence).
Put a version of the 6x5 with the refdes and separate traces in my IMPERFECTIONS thread.
[/EDIT]

 

[Robert]

Nice! Could it be simpler, like just a big cap in parallel with the LED?

A large cap could cause pops due to inrush current.

In addition to looking cool as it fades in/out, this has the advantage of gradually increasing the current to the LED, so no pops.

You could even adjust the values so the fade isn't visible, but still slow enough to reduce popping.

 

[genXslacker]

For anyone interested, MadBean's SSABP documenation provides some coaching on varying the timing.

The Cliff Note's version is to use a lower value (e.g., 4u7) for the cap that connects to the base of the BJT to speed up the fade on; decrease the value of the 22k resistor (e.g., 10k) to speed up the fade off.

Going the other way with the value changes prolongs the fading.

I breadboarded some variations before I put this in a pedal (last year?) and my recollection is that, for the purposes of the gimmick, the default values were about right. A slower fade seemed to me to be too gimmicky, even for a gimmick. Lowering to 4u7 and 10k seemed pretty quick, as I recall. I bet it wouldn't take too much lower than those before the fade wasn't apparent to the eye.