MiniDexed

MiniDexed is a FM synthesizer closely modeled on the famous DX7 by a well-known Japanese manufacturer running on a bare metal Raspberry Pi (without a Linux kernel or operating system). On Raspberry Pi 2 and larger, it can run 8 tone generators, not unlike the TX816/TX802 (8 DX7 instances without the keyboard in one box). Featured on HACKADAY.

Features

• Uses Synth_Dexed with circle-stdlib
• SD card contents can be downloaded from GitHub Releases
• Runs on all Raspberry Pi models (except Pico); see below for details
• Produces sound on the headphone jack, HDMI display or audio extractor (better), or a dedicated DAC (best)
• Supports multiple voices through Program Change and Bank Change LSB/MSB MIDI messages
• Loads .syx files from SD card (e.g., using getsysex.sh or from Dexed_cart_1.0.zip)
• Menu structure on optional HD44780 display and rotary encoder
• Runs up to 8 Dexed instances simultaneously (like in a TX816) and mixes their output together
• Allows for each Dexed instance to be detuned and stereo shifted
• Allows to configure multiple Dexed instances through performance.ini files
• Compressor effect
• Reverb effect

Introduction

Video about this project by Floyd Steinberg:

System Requirements

• Raspberry Pi 1, 2, 3, 4, or 400 (Zero and Zero 2 can be used but need HDMI or a supported i2s DAC for audio out). On Raspberry Pi 1 and on Raspberry Pi Zero there will be severely limited functionality (only one tone generator instead of 8)
• A PCM5102A or PCM5122 based DAC, HDMI display or audio extractor for good sound quality. If you don't have this, you can use the headphone jack on the Raspberry Pi but on anything but the Raspberry 4 the sound quality will be seriously limited
• Optionally (but highly recommended), an LCDC1602 Display (not i2c) and a KY-040 rotary encoder

Usage

• In the case of Raspberry Pi 4, Update the firmware and bootloader to the latest version (not doing this may cause USB reliability issues)
• Download from GitHub Releases
• Unzip
• Put the files into the root directory of a FAT32 formatted partition on SD/microSD card (Note for small SD cards which are no longer sold: If less than 65525 clusters, you may need to format as FAT16.)
• Put SD/microSD card into Raspberry Pi 1, 2, 3 or 4, or 400 (Zero and Zero 2 can be used but need HDMI or a supported i2c DAC for audio out)
• Attach headphones to the headphone jack using SoundDevice=pwm in minidexed.ini (default) (poor audio quality)
• Alternatively, attach a PCM5102A or PCM5122 based DAC and select i2c sound output using SoundDevice=i2s in minidexed.ini (best audio quality)
• Alternatively, attach a HDMI display with sound and select HDMI sound output using SoundDevice=hdmi in minidexed.ini (this may introduce slight latency)
• Attach a MIDI keyboard via USB (alternatively you can build a circuit that allows you to attach a "traditional" MIDI keyboard using a DIN connector, or use a DIN-MIDI-to-USB adapter)
• Boot
• Start playing
• If the system seems to become unresponsive after a few seconds, remove usbspeed=full from cmdline.txt and repeat (details)
• See the Wiki for Menu operation
• If something is unclear or does not work, don't hesitate to ask!

Pinout

All devices on Raspberry Pi GPIOs are optional.

CAUTION: All GPIO numbers are chip numbers, not header positions.

GPIO	Device		Function	Direction	Comment
14	UART		TXD		OUT
15	UART		RXD		IN
18	DAC		CLK		OUT
19	DAC		FS		OUT
21	DAC		DOUT		OUT
02	I2C		SDA		IN/OUT
03	I2C		SCL		OUT
17	LCD		EN		OUT
27	LCD		RS		OUT
16	LCD		RW		OUT
22	LCD		D4		OUT
23	LCD		D5		OUT
24	LCD		D6		OUT
25	LCD		D7		OUT
05	ROTARY ENCODER	CLK (ENC A)	IN		default setting
06	ROTARY ENCODER	DT (ENC B)	IN		default setting
26	ROTARY ENCODER	SW		IN
12	PWM AUDIO	PWM0		OUT
13	PWM AUDIO	PWM1		OUT
07	SPI		/CE1		OUT
08	SPI		/CE0		OUT
09	SPI		MISO		IN
10	SPI		MOSI		OUT
11	SPI		SCLK		OUT
04	NONE
20	NONE

Downloading

Compiled versions are available on GitHub Releases. Just download and put on a FAT32 formatted SD card.

Building

Please see the wiki on how to compile the code yourself.

Contributing

This project lives from the contributions of skilled C++ developers, testers, writers, etc. Please see https://github.com/probonopd/MiniDexed/issues.

Discussions

We are happy to hear from you. Please join the discussions on https://github.com/probonopd/MiniDexed/discussions.

Documentation

Project documentation is at https://github.com/probonopd/MiniDexed/wiki.

Acknowledgements

This project stands on the shoulders of giants. Special thanks to:

• raphlinus for the MSFA sound engine
• asb2m10 for the Dexed software
• dcoredump for https://codeberg.org/dcoredump/Synth_Dexed, a port of Dexed for embedded systems
• rsta2 for https://github.com/rsta2/circle, the library to run code on bare metal Raspberry Pi (without a Linux kernel or operating system) and for the bulk of the MiniDexed code
• smuehlst for https://github.com/smuehlst/circle-stdlib, a version with Standard C and C++ library support