The waveshaper used is fairly simple; Since the PT-80 output is a squarewave, a PLL is used as a frequency multiplier using a CMOS counter which in turn drives a R2R network to output a sawtooth output. By routing the PLL VCO input to different outputs of the counter, selectable with a switch, i got a simple way of selecting octave range.

Despite the fact that i'm only having a 6-bit output, the sawtooth is suprisingly even.



The 150pF cap should possibly be replaced with a cap in the 680pf - 1nF range to get better response.

At first i was trying to use the smoothing cap as a triangle output, but since this is my first PLL experience i decided to go with the more obvious sollution.