I completed the first Arduino based controller. It has a single control voltage and a single gate, both directly wired to a male 3.5mm connector. Using serial commands over the USB connection, it allows specifying the control voltage between 0 and 5V(*), and the binary gate value (TTL logic).
*) although the design was meant to go up to 5V, the voltage controller in the cheap Arduino Nano that I purchased on Ebay only delivers up to 4.57 Volt.
This is how it connects to a computer:
A look at the inside of the 50x25x25 mm aluminium enclosure. I would not have been able to fit many more components in this box.