This $20 synthesizer sounds very nice indeed

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"BPSynth is a #diy monophonic #virtualanalog #synthesizer based on a STM32F411 'BlackPill' microcontroller created by @Synthetech . In this video, I show which parts you need, where to get them and how to assemble them, plus some sound impressions. Table of contents:

00:00 short demo
00:07 hi
00:30 parts needed
00:58 were to get and how to install the firmware
02:23 building the BPSynth
04:20 building the MIDI jack
06:50 important considerations
07:14 set up a MIDI controller
07:39 synth engine overview
08:07 demonstation track
11:14 conclusion

Resources [active links here]
Firmware can be found on Blaines' YT channel: @Synthetech
BlackPill STM32F411 board https://de.aliexpress.com/item/100500...
UDA 1334A DAC module https://de.aliexpress.com/item/100500...
5pin midi socket https://de.aliexpress.com/item/330301...
6N137 optocoupler https://de.aliexpress.com/item/100500...
220 and a 10k ohm resistor https://de.aliexpress.com/item/100500...
1N4148 diode https://de.aliexpress.com/item/100500...
Jumper wires https://de.aliexpress.com/item/100500...
Breadboard https://de.aliexpress.com/item/100500...

HÄLP ZIS CHANNEL
https://www.patreon.com/floyd_steinberg
https://floydsteinberg.gumroad.com/
https://floydsteinberg.bandcamp.com/"

Synthetech videos:

BP Synth.. a DIY Virtual Analog Monosynth

video uploads by Synthetech



BP-Synth Code Tutorials

video uploads by Synthetech

Additional videos on YouTube.