MiniDexed Shield: A(nother) MiniDexed Pcb

[miotislucifugis]

Id like to share my new version of a miniDexed PCB:

I wanted to make something that is compact and full-featured, while still keeping it as simple/ inexpensive as possible and friendly for DIY beginners. (While I initially wanted to make my "ideal" minidexed, just for me!) I am the repair tech at a synth museum and I often get requests to do "DIY Synth building workshops." Usually, I turn them down because Ive never really found a circuit that is both simple enough for beginners to build in one sitting and that is also a nice, worthwhile, and playable instrument. (Personally I find most of these simple square wave/ drone/ optical theremin/ noise maker-type synth projects rather dreadful.) MiniDexed has long been a contender, but I needed a solution that puts it all together in a tidy, permanent package and avoids fussy dupont jumpers and some kind of costly/impractical (at least for for class settings) 3d printed enclosure the keep everything together. Also, it needs to keep the part count to a minimum and use (mostly*) through hole components. The "shield" format seemed ideal (yes, i know that for pi, they are technically called "hats", but to me they are all "shields"... anyway...)

Voila:

It uses all easy to source, off-the-shelf parts : a 1602 LCD, a cheap and cheerful (yet impressively good ) PCM5102A DAC module, an encoder, and of course, a raspberry pi. It features 2x 1/4" output jacks and a stereo 3.5mm jack for the Audio Out, TRS (type A) Midi IN and OUT. User configurable solder pads allow for a few different audio routing options: mono summing on the 1/4" jacks, bypassing the 1/4" jacks when a 3.5mm cable is is connected, and Direct out or Master Volume control

It can be built minimally with just the main board (+ Screen, Dac and encoder), or with an optional "Control" expander board that raises the encoder to make it easier for panel mounting, and/or or adding a Master Volume control. 3 different types of GPIO expander boards accomodate different types of GPIO buttons - either 5x pcb tactile switches or 4x (socketed) Kalih Choc or Cherry MX key switches.

• The keyswitch boards have some SMD parts, but are still very doable for beginners: 4x pull up resistors, and the 4x key switch sockets)

(Im still fleshing it out, but eventually) more info ( kicad files, build guide, minidexed.ini config, etc) can be found on my github:
https://github.com/miotislucifugis/MiniDexed-Shield

[Kirtai]

Oh this is very cool :)
Your link to your repo needs fixing though.

[miotislucifugis]

thanks!

[blixabloxa]

Looks great. Thanks for sharing.

[Gitarrenzupfer]

Very cool! Is the master volume control digital or analog. Could you please explain it in detail?

[miotislucifugis]

Its simply a dual 100k audio taper pot on the output. Ill try to put up a jpg schematic soon.

[Gitarrenzupfer]

I found the schematic already, but I could find the value of the pot. Anyway, a jpg schematic would be helpful für anybody...
Thank you 👍

[miotislucifugis]

In general, the value is not super critical, 100k - 1m will work. Be sure to use Audio taper tho'. Schematic, build guide etc are all on my to "do list"

[miotislucifugis]

Btw, if any one is interested in PCBs, full kits, or completed devices, just ask. ( I may eventually put them on my reverb/etsy shops and the Discord Linear night market channel,(... another thing on my list.)) I do have a few boards from the prototype batch that have a few minor errors (nothing major) that I would be happy to give out for free (+ shipping, of course... or you can pick them up in lovely Fribourg, Switzerland! ) You can contact me via email : charbot at gmail

[BobanSpasic]

Any possibility to add standard DIN connectors for MIDI as an add-on board?
I am interested in a PCB, possibly with pre-soldered components (excl. Pi, display and DAC)
I am located in Vienna, Austria.

[miotislucifugis]

There is no room to directly solder DIN jacks, but you could make a daughter board or use panel mount jacks and wire them from the 3.5 jack pads. Send me a email and we can discuss the details. I added my contact to the previous post.

[diyelectromusic]

That build/board looks amazing :)

I have found in my own pcbs that it is possible to overlap MIDI TRS and DIN footprints on the board as an option, but looking at your board that might make it slightly longer, and maybe a little wider...

Here's an example for my RPi 400 MiniDexed board: https://diyelectromusic.com/2023/12/18/rpi-400-midi-and-audio-pcb-design/

I can't claim credit mind - I pinched the idea from the Adafruit MIDI Feather Wing!

Kevin

[miotislucifugis]

Hey thanks!
It would have to be longer and thicker - the height of the jacks are a bit taller than the pi + header. And then it would mess with the spacing and layout of the controls/screen which i fussed over for quite a bit. At first, I really wanted DIN jacks and I definitely tried cramming it all in, but there was really no way w/o making it chunkier than I wanted. Trs seemed like a fair compromise, because as a whole, it looked better, and with midi on the side + power and audio out of the back... w/ some stout DIN cables plugged in, and 2x 1/4" cables... the whole ensemble starts getting kinda clunky.

I have to admit tho', Im really starting to appreciate (even love) trs midi (only type A, of course!) and have embraced it for a few other projects. It is perfect for diminutive pocket-sized synths like this and is great for travel / small desktop setups. DIN-TRS adapter are pretty common nowadays and personally, I welcome the thinner( and usually shorter) cables.