Adding blinking indicator light to tremolo footswitch

[mattmayhem]

TLDR: Given a standard vintage fender tremolo footswitch, what circuitry would be needed to add an LED that blinks with the tempo of the tremolo? Anyone willing to help me out or draw something up?

Full Story: I use a super compact pedal board with all mini pedals so about a year ago I built a reverb/trem footswitch. It has LED indicators for on/off and works with all my amps that have the traditional vintage fender footswitch set up. Recently however, I read that my new magnatone's footswitch would flash the tremolo indicator light in time with the trem tempo, and sure enough, the footswitch blinks the trem tempo with all my amps! So I opened it up to see if i could understand what's going on in there, but the PCB with surface mount components is totally opaque to me... Looks like there are a couple footswitches out there that do this (magnatone and swart at least). Anyone have any idea how they achieve this? Any info, links, drawings, etc would be super helpful. Thanks!

[mattmayhem]

Just in case anyone stumbles upon this later, here's what I did that seems to be working with all 8 of my amps from the Fender Custom Vibrolux and Vibro-Champ to the Magnatone Panoramic Stereo and Gretsch 6161 (all bias modulated trem). Feel free to critique, add comments or improvements, etc...

[antonis]

You can use on-off indicator LED as Rate blinking indicator also by simply wire it in series with LFO transistor Collector resistor..
(which resistor might need undersizing a bit due to extra LED forward voltage drop..)

e.g. on following schematic (part of EA regenerated tremolo..) original Collector resistor value was 15k..