Sync LED with Delay time - PT2399

[dulcetpine]

I want to have an LED that blinks in sync with the delay time of a pt2399 based delay pedal.  I did a few searches but couldn't find an answer, does anyone have any suggestions on how to achieve this?

[R.G.]

Sure.

The delay time of a PT2399 is 684,000 clocks. Take the output of the clock pin and divide it in a digital divider by 684000. The result is an LED that blinks on and off at the delay time. Your divider chain has to be able to run correctly with a clock at over 22Mhz to function properly at short delays. 68400 has factors of 2^4, 5^3, 3^2, and 19, so you'll need to divide the actual clock down by those factors to get the timing to blink the LED once.

There may be some design work required to get this set up properly.  

I would approach this with a four-bit 74ACT counter chip to divide by 16, to get down to 4275x the LED rate, then a pair of  divide-by-five stages to get down to 55kHz max and only count every 171-th pulse for making the LED go. I'd use an 8-pin PIC to do the count-to-171 and blip the LED with a fixed-time pulse every time the count-to-171 rolled over. Three 16 pin hard logic chips and a PIC should do it fine. The alternate is to use a maybe four more hard logic dividers and a one-shot for the driving the LED.

[R O Tiree]

Here's the schematic, hard-wired logic but without using a PIC, as RG has suggested:



There's a vero board for something very similar, but some have experienced clicking in time with the LED flash with this layout. I did this as part of an Echo Base +++ build (included tap-tempo, LED flash and a bunch of other stuff) and it was on a PCB using isolation routing. I also kept digital and analogue grounds separate. It shouldn't take me too long to knock up a daughter-board if you'd like? You can either etch it yourself or I can fab it for you for a small consideration.

Basically, the CLK signal from pin 5 of the PT2399 goes into pin 10 of the first binary counter. This counts up to 1024 and the resulting pulse resets the first counter and clocks the second counter. The second counter counts up to a total of 668 (times 1024 = 684032 clock cycles) and those diodes act as a poor-man's AND gate - when all the selected pins are high counter 2 gets reset. When pin 14 is high, the LED gets switched on for a short time.

It is important that you use a separate power supply (7805, caps, protection diode, etc) for this daughter board and that the wire connecting to pin 5 of the PT2399 (clock out) is kept as short as possible.

[ascianabhro]

cant find the link of the schematic, can somebody post the link again