This circuit is built around the Spin Semi FV-1 DSP chip.
This (too long) demo shows some programs I have been working on:
Most of the effects were created with the great SpinCad software created by Digital Larry. Some are parts of available code stitched together (still have a lot to learn in that respect)
Apart from the circuitry supporting the FV-1 chip, you can see an input buffer and a mixing stage mixing the buffered direct signal with the output of the FV-1. The hardware mixing works fine in most cases and avoids dedicating one of the 3 pots controlling the FV-1 parameters. Sadly with some programs where the signal coming from the FV-1 is too similar to the direct signal, there is some phasing effect because of the very slight latency introduced by the DSP.
I also added a hardware feedback path that takes the right output of the FV-1 and feeds it back to the right input through a pot.
The 8 programs loaded in the external EEPROM are selected with an 8 position rotary switch and a network of diode logic.
The POT0 input on the FV-1 is connected to either a pot or the jack for external expression input. A momentary switch is also inserted to this input. A 4 position rotary selects between the use of the pot or expression input each time with the option to have the momentary switch going high or low.
I added the momentary switch mainly to use it for an infinite reverb effect (freeze) and also for tap tempo.
There is a 3 pin connector on the PCB to allow programming the EEPROM in circuit.