MT32-Pi for Atari ST

Blogs & guides and tales of woo by forum members.
Post Reply
Posts: 19
Joined: Fri Jan 14, 2022 2:43 pm

MT32-Pi for Atari ST

Post by elterwater »

Just wanted to share my build journey for this lovely little project. As many people know one of the key strengths of the Atari ST was the built in MIDI capabilities. But if, like me, as a youngster in the 90s you were too poor to actually connect anything to these ports, the MT32-pi project comes to the rescue to provide synthesiser emulation!

Credits to Dale Whinham for the baremetal kernel project

and Chrissy for the PCB design: ... i-midi-hat

Chrissy's board design is very simple and cheap to put together per-board, but downside is that you end up needing to order 5 of everything to make it worthwhile placing an order with places like mouser :/

The project is compatible with Pi Zero 2 (not original Pi Zero), Pi3 and Pi4 boards. I have built some with both Pi Zero 2 and Pi3 A+ and honestly there's no benefit from the Pi3 over the Pi Zero 2 except the overall stack is much more stable as the PCB is twice the size of a Pi Zero 2 and so is a little top heavy.

Important gotchas to note

1. Pay attention to Dale's wiki guide and in particular the soldering of the jumpers beneath the GY-PCM5102 DAC module as these will most likely arrive unsoldered. If you forget to do these, then you'll spend time scratching your head wondering why there's no output and then having to solder jumper pads in a tight space.... ... DAC-module

2. As of September 2023, I found that my recently purchased Pi 3A+ boards from ThePiHut were not compatible with the default distribution package available from Dale's github repository. This resulted in my Pi board blinking the green LED a four slow times then five fast times and failing to boot. You will need to replace the start_cd.elf on the sd card with a more recent version from the official Raspberry Pi firmware-master: ... aster/boot

The build

This is a short pictorial guide to how I built mine, there are probably much better ways to build but this method suits my ham fisted soldering skills.

1. Start with the GY-PCM5102 DAC board first. As mentioned in Gotchas, you will need to solder the pads as per Dale's guide if they are not in the correct jumper position, otherwise you'll hear no output.

MT32pi-1.jpg (130.3 KiB) Viewed 233 times
MT32pi-2.jpg (185.88 KiB) Viewed 233 times

I would also strongly suggest adding additional solder blobs to the five contacts around the 3.5mm headphone socket. The default from the factory has the contacts sitting ON TOP of the board solder pads and the entire socket comes away from the PCB with the slightest touch. The additional solder should help keep everything in place.

MT32pi-3.jpg (168.72 KiB) Viewed 233 times
MT32pi-4.jpg (229.58 KiB) Viewed 233 times

2. Here's the bare PCB delivered from JLCPCB, very simple and well labelled. There are choices you will need to make about which DAC board, which orientation of OLED display (square or oblong) etc which will steer other details such as arrangement of buttons.

MT32pi-5.jpg (213.02 KiB) Viewed 233 times

3. I start with soldering the diode and two resistors first.

MT32pi-6.jpg (226.21 KiB) Viewed 233 times

4. The optocoupler next to give maximum access to the six pins before adding on the capacitor. Note the orientation of the optocoupler dot to the board.

MT32pi-7.jpg (206.38 KiB) Viewed 233 times

5. Add the capacitor, the DIN port and the 2x20 header block for the interface to the Pi.

MT32pi-8.jpg (224.59 KiB) Viewed 233 times
MT32pi-9.jpg (133.03 KiB) Viewed 233 times

6. Data pins for the DAC board and then the GND support pin

MT32pi-10.jpg (187.66 KiB) Viewed 233 times

7. Mount the DAC board

MT32pi-11.jpg (215.51 KiB) Viewed 233 times

8. Then add the control buttons and a screen.

MT32pi-12.jpg (243.97 KiB) Viewed 233 times

9. Prep your SD card as per Dale's instructions and updating the start_cd.elf file if required. Connect it all up with audio output from the DAC board into your favourite speakers and a MIDI cable to the MIDI-OUT of your ST.

10. In best Blue Peter tradition, here's one I made earlier mounted to a Pi Zero 2 :)

MT32pi-fin.jpg (241.83 KiB) Viewed 233 times

There are a few games which make use of the MIDI out capabilities to give you some lovely tunes, such as BombJack and many titles released by Sierra. These sometimes have a habit of outputting both sound chip music via the normal channels and the MIDI port simultaneously so you'll need to work out a way of mixing the two together....

I've not managed to coax Pro MIDI player into playing any of my internet downloaded MIDI files as it doesn't recognise them. I'm currently exploring Midi Music Maker by Dave Henry to play those MIDI files. There are guides elsewhere (follow Dale's Wiki) on sourcing the correct ROM files to make this all work and a variety of different soundfonts for you to experiment with.

Hope this helps someone out there!
User avatar
Posts: 230
Joined: Sat Sep 08, 2018 3:10 pm
Location: Brooklyn & Edinburgh

Re: MT32-Pi for Atari ST

Post by stween »

Nice work. And, time to link again to this:
User avatar
Posts: 180
Joined: Sun May 08, 2022 6:11 pm
Location: The Midlands

Re: MT32-Pi for Atari ST

Post by chronicthehedgehog »

Yes it's a pretty cool device. That Bombjack midi soon gets annoying though :D although it was a novelty at first.

+1 to trying the scumm-st games. The games (Monkey Island etc) were going really cheap at GOG.COM recently
Post Reply

Return to “MEMBER BLOGS”