My multiplex chips turned up as planned, and so I really got stuck in today. Firstly, I rebuilt my ISP (programmer) onto a piece of stripboard. This is something I will need to use a lot in the future, so building something a little more permanent made a lot of sense. It also freed up one of my breadboards, which would be useful for the next part of my day – building bigger breadboard prototype utilising the CD4051 multiplexer chip, as well as a proper mode switch and eight pots rather than just the one.
This building process was done in tandem with a lot of coding, and I have ended up with all modes and inputs working (the multiplexer works like a dream!). Currently there are no outputs or the ability to actually run a sequence, but that will be a job for tomorrow…
I also had a bit of a think about how the CV inputs will work. At the moment I am just using pots with a nice easy voltage range from 0-5V – exactly what my ADCs can work with. However, my plan is to augment each input with a CV control as well, mixing the 05V from the pot with an external source – most likely an LFO or another sequencer. Eurorack modules could potentially throw anything from -12V to +12V into my inputs, so I need to make sure that my circuitry is protected, and also that my expected CV input range (-5V to +5V) works nicely with my inputs. The diagram below is a first attempt at a design that will achieve this. The section on the right with the diodes should limit the signal to between the 0-5V range that I need. This is based off some schematics from the Doepfer website. I will need to order some parts and test this with a multimeter next week…
