@themagpi We've merged in preliminary Raspberry Pi 5 support to MiniDexed thanks to Rene's excellent Circle bare metal OS now supporting it. It's still considered experimental and doesn't currently do anything a Pi 3 or 4 can't do, but it does appear to work.
The photo is me testing PWM audio output on my Pi 5.
Ha! Neat. I've just realised I can enable MIDI THRU for my RPi 400 PC keyboard to my serial MIDI interface and turn it into a MIDI keyboard controller via MiniDexed :)
Taking a typical “low to high” soldering approach, this is the suggested order of assembly:
Disc capacitors.
Button switches.
GY-PCM5102 module (if used).
4-way header for display.
GPIO header.
Rotary encoder.
Build Options:
With DAC: As described below with a GY-PCM5102 module on the board. The display will have to be fitted in a 4-way header socket and raised above he PCM5102 once fitted.
External I2S DAC: It is possible to use something like the Pimoroni Audio DAC SHIM between the Zero and the MiniDexed IO board. More details here: A DX7 USB Dongle.
Note: in the case where the SSD1306 is soldered directly to the board, e.g. if no PCM5102 is used, the 100nF ceramic capacitor for its supply pins will have to be bent over flat prior to mounting the display.
The key elements of the minidexed.ini configuration required to support this board are as follows.
# If in USB Gadget mode - see <a href="https://diyelectromusic.wordpress.com/2023/11/22/a-dx7-usb-dongle/">A DX7 USB Dongle</a>.<br></br>USBGadget=1<br></br><br></br># Either pwm or i2s<br></br>SoundDevice=i2s<br></br><br></br>LCDEnabled=1<br></br>SSD1306LCDI2CAddress=0x3C<br></br>SSD1306LCDWidth=128<br></br>SSD1306LCDHeight=32<br></br>SSD1306LCDRotate=1<br></br>SSD1306LCDMirror=0<br></br>LCDColumns=20<br></br>LCDRows=2<br></br><br></br>ButtonPinPrev=0<br></br>ButtonActionPrev=<br></br>ButtonPinNext=0<br></br>ButtonActionNext=<br></br>ButtonPinBack=5<br></br>ButtonActionBack=click<br></br>ButtonPinSelect=11<br></br>ButtonActionSelect=click<br></br>ButtonPinHome=6<br></br>ButtonActionHome=click<br></br>ButtonPinShortcut=11<br></br><br></br>EncoderEnabled=1<br></br>EncoderPinClock=10<br></br>EncoderPinData=9
Closing Thoughts
Whilst it is somewhat irritating to have made the 10p/10n mistake yet again, I’m quite pleased with how these boards have come out.
I have a stackable TRS MIDI interface in the works too which should be able to work with this IO board too.
The amazing Rene Stange added USB Gadget (i.e. device) support to the Circle bare metal Raspberry Pi environment a while ago so I’ve now incorporated that into MiniDexed. This allows MiniDexed to be used as a USB device – i.e. it can just be plugged into a PC and used via USB MIDI directly, as long as your Raspberry Pi supports USB Gadget mode and you have some means of audio output.
This post looks at how to make a “USB dongle” that is basically a USB MIDI accessible DX7.
A quite note before I start however. Why would someone want to do this? There are several VST DX instruments for PCs if you want DX sounds in your DAW and Dexed itself gives you full access to a DX7 via a software interface.
So there is probably very little practical reason to do this. But personally, I just couldn’t resist the idea of having a plug-in DX7 on a USB stick!
If you are new to microcontrollers and single board computers, see the Getting Started pages.
Parts list
Raspberry Pi Zero, Zero W or Zero W2.
I2S or alternative audio output for a Pi Zero.
USB “STEM”, “Zero Dongle” or other USB device connection (micro USB to USB A).
Note: the Pi Zero and Zero W will give access to a single MiniDexed tone generator. The Pi Zero W2, will support 8 tone generators.
Warning: When using a Raspberry Pi in USB Gadget mode, do not plug in its usual power supply! It should be USB “bus powered” only.
The Hardware
Whilst any Raspberry Pi that supports USB Gadget mode could be used with a suitable lead to power and link to MiniDexed, to make a USB “dongle” requires the use of a Pi Zero (any flavour) and a “dongle style” add on.
It will also need a means of outputting audio from the Zero as MiniDexed only supports USB MIDI, not USB audio.
There are several options for audio out on a Pi Zero. By far the easiest is some kind of off-the-shelf I2S audio interface.
A really good, low-profile one ideal for use as a dongle is the Pimoroni Audio SHIM, which can be found here. It doesn’t even need soldering, it can push-fit over the Pi’s GPIO headers, but any I2S audio interface for the Pi can be used as long it doesn’t interfere with the USB plug for the “dongle”.
My ideal combination is the USB STEM and the Pimoroni Audio SHIM as it is both low-profile and has the USB plug at one end and the audio output at the other.
Hopefully by the time you read this, USB Gadget support in MiniDexed will be merged into the main code (it is PR567). Details of how to configure it can be found on the wiki here, but the key MiniDexed configuration (minidexed.ini) required for this configuration is as follows:
USBGadget=1SoundDevice=i2s
The rest of the configuration is largely ignored, but things like the LCD, buttons and encoder can simply be disabled (set to 0) as they are not required.
A Single DX7
As mentioned previously if using a Zero V1/W then a single tone generator is available. The MIDI channel it uses will be as defined in the default performance.ini file. It is set to OMNI by default. To change it, change:
MIDIChannel1=<MIDI channel 1 to 16>
The default MIDI configuration for MiniDexed assumes voice changes will be made with a combination of bank select Control Change and Program Change messages with each bank containing 32 voices. But the following configuration allows four banks to be spread across all 128 Program Change values:
ExpandPCAcrossBanks=1
When plugged into a PC it will come up as “MIDI Gadget” as a USB MIDI compatible device. Here it can be seen in MidiOx, being selected as the MIDI output.
I have a MidiOx instrument file with all the voices for Roms 1a/1b/2a/2b/3a/3b/4a/4b selectable via Bank Select messages, and Roms 1a+1b+2a+2b configured for use as a single 128-voice bank via Program Change messages.
Find it on GitHub here. This needs to be copied to the “instr” directory of the MidiOx installation.
In MidiOx, View -> Instrument Panel, select “INS File: DX7ROMS.INS” and then choose one of the following for “instr”:
“YAMAHA DX7 ROMS” for the individually selectable 8 ROMs.
“YAMAHA DX7 VOICES” for the first four ROMs to be linked as a 128-voice single bank.
Both views (and voice selections) are shown below.
If using a Zero 2W then 8 tone generators are available. In that case there is a choice. It can be treated as eight independent tone generators, in which case the MIDI channels for each TG should be set independently.
The following configures TGs 1-8 for MIDI channels 1-8.
At this point, the MIDI interface is the same as before, but changing the MIDI channel will change the tone generator being used.
Alternatively, it is possible to now treat the 8-way TG MiniDexed as a single instrument with much more complex sounds.
If the following setting is enabled in minidexed.ini:
PerformanceSelectChannel=1
This will interpret Program Change messages on MIDI channel 1 as selecting “performances”. Each “performance” is a configuration of up to 8 tone generators with a range of voices and effets.
At present, MiniDexed loads performances into consecutive “slots” meaning that the numbers in the MiniDexed repository do not relate to the “patch numbers” used over MIDI. The MIDIOx file supports the files in the repository at the time of writing. If new performances are added in some of the gaps (and there are gaps) in the numbering, then the names will be out of sync with what is installed.
Personally I think we need to change this and make the numbers relate to the MIDI program numbers. Watch this space!
Closing Thoughts
As mentioned in the introduction, with a good selection of software synths available that provide a DX7 on a computer for use with a DAW, there is limited use for a “DX7 on a USB stick”.
But I still think this is a pretty neat thing to be able to do, if nothing else, just for the fun of knowing that a $2000 synth from the 1980s can now be replicated with ~$20 worth of hardware that can be plugged into any PC and just “played”.
@Raspberry_Pi
I've turned a discontinued #Pimoroni Speaker Phat into a #MiniDexed Phat in order to give a new lease of life to a slightly damaged Raspberry Pi 2 that I recovered from ewaste
I've been getting back to some making again, having done some more coding for #MiniDexed, played around with some bought kits from RaKit.
And on Saturday posted links to my #LoFiOrchestra classical performances in a #LoFiProms series - most of these had never been posted here on the Fediverse before.
Here is the build guide for my latest PCB - a bit of a niche one this - running two MiniDexed instances on two @raspberry_pi s to give 16 tone generators available over MIDI.
A1 Hello #MakersHour, Kevin here. Having missed out yesterday its nice to get another chance today :)
I've been out a lot these past few weeks, but I have now rebuilt my Linux machine which means I can get back to some #MiniDexed coding - assuming I can remember how to do it!