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A project log for hgSynth

ESP32 based monosynth embedded in bass guitar

Igor BrkicIgor Brkic 05/06/2018 at 22:020 Comments

So, I'm happy to say that progress is happening. I got the sound! And waveform on OLED. And initial web GUI.

First, a video of an OLED and the GUI (sound is really low and can be heard only at the end - it was late at night):

Now onto  technical details...

Web GUI

For HTTP and websockets server I used https://github.com/me-no-dev/ESPAsyncWebServer library. It is a really nice library with one downside - it includes FS and SPIFFS ("filesystem" on ESP32's flash chip) support and when it's included code uploading takes additional 20-30 seconds (if someone knows how to turn this off please let me know). It has a support for serving files directly from SPIFFS but I decided not to use it. Using it would require additional step of uploading html/js/css files to flash which is OK but I'd like to handle everything related to uploading code in one step. So, here's my kind of hackish solution - insert the whole web page in the code as a const value (this way it will be written to flash). To minimize the code I additionally decided to use just vanilla JS without external libraries and I think the final product is quite OK - UI controls are defined in variable and dynamically built so it's easy to change UI by just changing that variable. To convert the whole html page to C header file I wrote another Python script (data/convert_to_header.py) which takes html, removes some whitespace, escapes some characters and packs it into a C header file.

ESP32's WiFi in this case connects to my local WiFi but in the real case it should start in the soft AP mode. Actually, I was thinking to first check if some predefined WiFi is available and connect to it and if it's not then start as AP.

Synth

Currently, oscillators are implemented via simple (non-bandlimited) lookup table. Filter is Paul Kellet's design (http://musicdsp.org/showone.php?id=29) - it's quite usable but I'll probably switch to some other design.

This first prototype contained components directly soldered to ESP board and a lot of flying wires so I decided to implement it on perfboard. Unfortunately, I disassembled the first prototype without taking a photo of it.

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