NEED HELP CAVE DWELLER BLINKING TEMPO LED

[Briman1974]

HI,
I have built a cave dweller and I really like it. I have done the mod to the dwell pot already and I have also added a switch to go between bright and the standard darker repeats. What I really want to do is add a blinking LED to show the tempo of the pedal.
Has anyone done this?
Thanks in advance for your help.

[midwayfair]

The circuit required to do this properly is MASSIVE. You need a chip that can convert the clock output (see that unused pin on the PT2399 in the schematic? That's the clock output) into a control voltage for the LED. Actually, it turns out it involves two very large chips:
http://www.diystompboxes.com/smfforum/index.php?topic=102660.0

The blinking LED circuit is actually larger than the delay itself.

There are some other options. One is to build the Taptation tap tempo controller (JMK sells PCBs, and the necessary chipset is sold by DIYStompboxes for $20); obviously this involves a larger enclosure and a second footswitch.

One final option I can think of, and probably the smallest circuit that can do this, is to splice a transistor gain stage in before pin 3 of the Dwell pot. Send the emitter output (~ unity gain) to the dwell pot, then decouple the collector and create an envelope circuit to convert the audio into DC. Run the DC through an LED to ground and it will blink each time a repeat happens. This won't tell you what the tempo is when the pedal's switched off or you're not playing, but it might look cool.

Maybe someone else can think of a way to convert the clock signal to a ticking sound. That would reduce the size of the circuit in the first paragraph, but none of these are likely to be small enough to fit this pedal into a 1590A.

[Ettore_M]

The only way I can think of and it might be a small circuit, is with using a uC. An ATTiny could do the job, I guess. It could read the output frequency of the PT2399 and output a true/false signal to light the LED on and off.
But then again, don't ask me how it could be done. I know very little stuff for C and AVR programming.

Hector

[Briman1974]

Thanks Midwayfair! Wow! that's a lot of Diodes! Definitely a huge circuit. LOL. I thought it would be simple cause I've modded a lot of TR2's and have added a blinking LED. Those are pretty simple to do. There are also multiple ways to do it on those. I know the TR2s are a whole lot different circuit than the cave dweller.
Must be a limitation of the PT2399. Great sounding pedal though. Really am enjoying this build.