MCU-controlled dual PT2399 delay

[synchroton]

Hi, here's a new design I'm working on. Just sent out the first prototype.

The basic idea was to exclusively use resistive control over all parameters of the delays (feedback, mix, and delay time) and use a digital sextet potentiometer to do it. So, six potentiometers to control the parameters, with six LED's and buttons. Pushing the switches change any potentiometer control between manual mode (value of the pot gets written directly to the digi pot) and automated mode (value of the pot affects some parameter of the effect algorithm) There are an additional two buttons (right now i'm thinking one is a "shift" button and one cycles through algorithms) but all of this is mutable in code.

The 4066 switches, I think, is a nice touch -- should let you decide whether input 1 goes to delay 1, delay 2, or neither, whether input 2 goes to 1, 2, or neither, and whether the feedback is engaged for either delay or whether the output is coupled to the input of the other delay. So you can have the delays connected serially or in parallel.

The MCU is an ATMEGA328, I'm going to use the Arduino bootloader and simple RX/TX/RESET arrangement for easy programming by people familiar with it.

Any comments/suggestions are welcome -- Here's a list of current issues:

- My feedback didn't quite have the range I wanted, I can go into self-oscillation but the # of repeats at minimum (full 100k resistance at the digi pot) is still pretty high.

- not sure what's going to happen with my VCC/2 - I'm pulling it off of the PT2399's, and joining them to a 10uF cap. This is my bias for the op-amps.

- I believe the input is out-of-phase with the feedback. This will probably be strange...

- traces are routed very poorly, and in close proximity to one another... I'm using Eagle Light so I was extremely limited, and am trying to get far too much circuit in far too little space. (10mil traces/8 mil width)

- I'm concerned about feedback resistors around my 4066 switch coupling the inputs to the wrong outputs when the 4066's are engaged.

- the output is just a voltage follower with current limiting resistor - I didn't want to change the gain at the output, but not sure if this is the best.


In retrospect, I probably would have used VCA's for the feedback, driven by filtered PWM output. Currently I'm using PWM to drive LEDs. I could've used the I/O expander but it would have been very slow. And harder to code. Trying to avoid as much PWM noise as I can.

Also I've heard that using a current sink is a better way to control the delay time (not sure why though) and I could've used a PWM control voltage there as well...

Any revisions I make to this design will have to take up less board space, rather than more, given that everything is currently shoe-horned in.



feel free to do anything with this design. I hope to sell these, but I encourage anyone to build it themselves if they so desire, or modify the schematics. Keep in mind this is just the prototype, but I'll be 'open-sourcing' the design.

[DrJustice]