This project attempts to build a low-cost analog synthesizer based on well-available components like LM324 or TL084 op-amps, which is easy to understand and learn.
The goal is a semimodular synthesizer which is compatible to existing other systems, where possible. The following features are planned:
For the sake of simplicity, the following trade-offs are being made:
So far, apart from standard resistors and capacitors, the synth uses LM324 op amps, and BC547 / 2N3904 bipolar-junction-transistors and 2N7000 MOSFETs.
The control logic and its firmware is currently based upon a STM32F103 based "blue pill" board, which can be sourced for less than 2 EUR from your favourite chinese seller. (Note: look for those boards with a rectangular white reset switch, not a flat round one.) Previous versions were developed for the STM32F411 discovery board, which should still work after adjusting the Makefile.
under simulation/
, some circuitry was tested (using the KiCAD SPICE
simulation).
Most importantly, simulation/vco
shows a functional exponential VCO. There
are detailed annotations on which part serves which purpose.
simulation/software/ contains tooling to do transient simulation on parts of the synth with different control voltages and to further analyze the results.
Under measure_vco/
you can find the tooling and test results for measuring
the pitch deviation of the VCO.
hardware/ contains the actual hardware boards and drafts:
To build libopencm3:
git submodule update --init
make -j8 -C libopencm3
If you're using a STM32F411 board, you must adjust measure_vco/firmware/Makefile
and use the DEVICE=stm32f411re
instead of the DEVICE=stm32f103c8t
line.
To measure the vco frequency response:
cd measure_vco/firmware
make
then do whatever is neccessary to flash the program onto your board. For the blue
pill board, putting it into bootloader mode by jumpering BOOT0 to 1, resetting, and
calling stm32flash -w dac_test.bin /dev/ttyUSB0
does the job, while for my
STM32F411-discovery, which has a non-standard blackmagic firmware on the STLINK chip, it is:
arm-none-eabi-gdb dac_test.elf # make sure it loads the .gdbinit file
load
run
Connect the pins correctly, then record the output with an UART adapter (or using the blackmagic uart device).
All software, firmware and schematics are released under the terms of the GPL3 license.
Note that this does not include the simulation/**/*.lib
files needed for
simulation. Vendor licensing as noted in the respective files applies.