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MiniDexed
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MiniDexed

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 Pi Raspberry 2 and larger, it can run 8 tone generators, basically creating an open source equivalent of the TX816/TX802 (8 DX7 instances without the keyboard in one box).

Features

  • Uses Synth_Dexed with circle-stdlib
  • SD card contents can be downloaded from GitHub Releases
  • Runs on Raspberry Pi Zero, Raspberry Pi 1, 2, 3, 4, 400
  • produces sound on the headphone jack, HDMI (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

TODO

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 or 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 alphanumeric 1602 LCD Display 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
  • 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
  • Boot
  • Start playing
  • See the Wiki for Menu operation

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 locally

If you need to build the source code yoursel, you can use the following example, e.g., to build for Raspberry Pi 4 on a Ubuntu 20.04 build system. See build.yml for complete build steps that create versions for Raspberry Pi 1, 2, 3,and 4 in 32-bit and 64-bit as required.

# Choose your RPi
export RPI=4

git clone https://github.com/probonopd/MiniDexed
cd MiniDexed
mkdir -p kernels sdcard

# Recursively pull git submodules
git submodule update --init --recursive

# Install toolchain
if [ "${RPI}" -gt 2 ]
then
	wget https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-aarch64-none-elf.tar.xz
else
	wget https://developer.arm.com/-/media/Files/downloads/gnu-a/10.3-2021.07/binrel/gcc-arm-10.3-2021.07-x86_64-arm-none-eabi.tar.xz
fi
tar xvf gcc-arm-*-*.tar.xz 
export PATH=$(readlink -f ./gcc-*/bin/):$PATH

# Build dependencies and MiniDexed
./build.sh
cp ./src/kernel*.img ./kernels/

# Get Raspberry Pi boot files
cd ./circle-stdlib/libs/circle/boot
make
if [ "${RPI}" -gt 2 ]
then
	make armstub64
fi
cd -

# Make zip that contains Raspberry Pi 4 boot files. The contents can be copied to a FAT32 formatted partition on a microSD card
cd sdcard
../getsysex.sh
cd ..
cp -r ./circle-stdlib/libs/circle/boot/* sdcard
rm -rf sdcard/config*.txt sdcard/README sdcard/Makefile sdcard/armstub sdcard/COPYING.linux
cp ./src/config.txt ./src/minidexed.ini ./src/*img ./src/performance.ini sdcard/
echo "usbspeed=full" > sdcard/cmdline.txt
cd sdcard
cp ../kernels/* . || true
zip -r ../MiniDexed_$GITHUB_RUN_NUMBER_$(date +%Y-%m-%d).zip *
cd -

# Optionally, create a RPi image. This can be written to a microSD card using tools like Etcher or dd
sudo apt install --yes  mount parted
IMG="`date +%Y-%m-%d`_minidexed-RPi${RPI}.img"
dd of="${IMG}" seek=50MiB bs=1 count=0
sudo parted "${IMG}" mktable msdos
sudo parted "${IMG}" mkpart primary fat32 2048s 100%
DEV=`sudo losetup --find --partscan --show "${IMG}"`
sudo mkfs.vfat -F 32 -n BOOT "${DEV}p1"
mkdir boot
sudo mount "${DEV}p1" boot
sudo cp -R sdcard/* boot
sudo umount boot
sudo losetup -d "${DEV}"
rm -r boot

# Write to SD card
sudo dd if="${IMG}" of=/dev/mmcblk0 bs=512k status=progress && sync

Discussions

https://github.com/probonopd/MiniDexed/discussions

Wiki

https://github.com/probonopd/MiniDexed/wiki

Acknowledgements