Been busy building a 5v µModular system for students to learn about and experiment with sound. Design should follow the classic synth setup like for example a Minimoog, with added patchpoints. Part of the design is finished, as follows:
Input of  is an Arduino PWM wave. This wave is passively filtered to a DC voltage (ranging from 0v to 5v). This resulting voltage will be one way to drive the voltage controlled oscillator.  is necessary to shift the voltage to a more musically interesting range including lower frequencies (-2v to 3v). The range is not amplified to i.e. -5v to 5v because the Arduino PWM only has limited resolution (10 bit = 1024 values). The shifted voltage is inverted because of the sawtooth oscillator under .
 shows the voltage scaler (1v -> ~18mV) and the exponential converter as already discussed on sinneb.net. The 1k tempco should be coupled to the CA3046 array.
and finally  shows the sawtooth core for the Senk. Previous designs of me had an inverting schmitt trigger followed by an inverting buffer in the waveform reset loop. This design features a non-inverting schmitt trigger, sidelining the inverting buffer and a number of resistors. Deploying of the BC550 resulted in the best waveforms, as shown by this youtube video:
Next features I’m working on:
Oscillator pulse out, oscillator sub out and mixer section.
Mixed waveform looking cool in simulation :) Output needs AC coupling.