MonoMiK

So, time to optimize signal count coming from the backplane. One important bunch of signals are the control voltages from the CPU. One idea is that you can store patches, even with those front panel knobs, which are true analog to the the attached electronics. There are some tricks that the CPU is able to scan those CVs in a simple way and then lock out the front panel knobs to provide the values from the CPU. To keep complexity low, only all panel knobs can be turned off together, so the software has to be able to help the user dial in the desired values when a stored patch has to be modified.

Besides those knobs, not much CVs are really needed. Each VCO pitch and VCF cutoff gets a separate CV line from the CPU, which controls keyboard tracking and larger detunes by software. The front panel knobs will be there for full realtime control without using the CPU, if front panel usage is desired. Older synths of the 80s use a similar way, but they usually have the CPU between the knobs and the synthesizer, so there is no infinite resolution for those controls. Here, it is not for stored patches, but it is for real front panel control.

As space on the backplane is very limited, i had to use SMD components here. The resistors you see in those photos are 0805 sized components. Not funny to solder them by hand to a veroboard with 100 mil hole distance. For size comparisons, the resistors are 80 mil long and 50 mil wide. 100 mil are 2.54mm, so you can have an idea about the size. During the soldering, one of the resistors fell down on the floor - no way to find it :)