Dusted off analog saw + ladder filter breadboard from 2014 and finally it is filtering. Together with the STM32F103 at $1.55 this is starting to look like an ideal Rust no_std playground.
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Starting out in C+ASM for critical parts (PDM DAC for CV). Saw+Pulse circuit is working. Not using HW temp comp for exp conv to simplify circuit. Will use digital regulator to tune it. Period measurement on STM is working using EXTI from saw discharge pulse. This is fun.
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I stopped working on this after I got the diode ladder working as well (original design!). It sounds like a rubber duck. I was so proud. Analog is hard. Meanwhile I bought a TD-3 to get rid of 303 envy, but the STM circuit is way more flexible. No time unfortunately...