Almost "All in one" MiniDexed IO Options

By Kevin on March 2, 2025

As I was browsing around I happened to notice a couple of interesting add-on boards that comprise a OLED display, rotary encoder and some buttons.

With the addition of a I2S DAC (or just using the existing PWM output) these make a really interesting option for MiniDexed IO.

Warning! I strongly recommend using old or second hand equipment for your experiments. I am not responsible for any damage to expensive instruments!

If you are new to microcontrollers and single board computers, see the Getting Started pages.

The Displays

There are lots of cheap display boards out there. These are the boards I've been looking at:

Which are called some variation of the following:

"0.96 inch OLED IIC 12864 OLED Display with 4x4 key I2C SSD1315 LCD Screen".
"1.3 inch OLED display screen with EC11 rotary encoder module IIC".
"0.96 inch OLED display screen with EC11 rotary encoder module IIC".

These particular ones have the following display parameters

SH1106 (1.3"), SSD1306 (0.96"), and SSD1315 (0.96" with buttons).

1.3" Encoder Display	0.96" Encoder display	0.96" button display
SH1106	SSD1306	SSD1315
128x64	128x64	128x64
2 Buttons	2 Buttons	4 Buttons
Switched Rotary Encoder	Switched Rotary Encoder

SSD1306 is directly supported by MiniDexed, but the other two are not. But it turns out that the SSD1315 display works fine as a SSD1306 and all three have the same I2C addressing scheme - 0x3C is the default.

The SH1106 based display however will need some updates to the core operating environment used by MiniDexed before it can be used, so for now that one can't be used.

0.96" Encoder Display

The following wiring and configuration should allow the use of this display with MiniDexed.

Raspberry Pi GPIO Connections

Display VCC	3V3	5V
Display SDA	GPIO 2 SDA	5V	DAC VIN
Display SCL	GPIO 3 SCL	GND	Display GND
	GPIO 4	GPIO 14 TXD
	GND	GPIO 15 RXD	Opt: MIDI IN
	GPIO 17	GPIO 18 PCM CLK	DAC BCK
	GPIO 27	GND
	GPIO 22	GPIO 23
	3V3	GPIO 24
Display TRB	GPIO 10	GND
Display TRA	GPIO 9	GPIO 25
Display PSH	GPIO 11	GPIO 8
	GND	GPIO 7
	ID_SD	ID_SC
Display BAK	GPIO 5	GND
Display CON	GPIO 6	GPIO 12
	GPIO 13	GND	DAC SCK / GND
DAC LRCK	GPIO 19 PCM FS	GPIO 16
	GPIO 26	GPIO 20
DAC GND	GND	GPIO 21 PCM DOUT	DAC DATA

Note: I ended up swapping TRA/TRB over (which can be done either in the wiring or in the definitions in minidexed.ini) to make the encoder operate in the direction I wanted.

I've also chosen to wire the "CONFIRM" button as a HOME button, but this could be used for SELECT if required. I'm using the encoders switch for SELECT.

The display board doesn't include any audio so a I2S DAC is highly recommended, which has to be connected separately. It is also possible to connect up a MIDI IN circuit to GPIO 15 (RXD) if required.

MiniDexed.ini Configuration

SoundDevice=i2s

LCDEnabled=1
SSD1306LCDI2CAddress=0x3C
SSD1306LCDWidth=128
SSD1306LCDHeight=64
ButtonPinBack=5
ButtonActionBack=click
ButtonPinSelect=11
ButtonActionSelect=click
ButtonPinHome=6
ButtonActionHome=click
EncoderEnabled=1
EncoderPinClock=10
EncoderPinData=9

It is possible to leave SSD1306LCDHeight=32 and then the display is double-height, but it is also a little grainy, so I prefer just to use half the display with a "fuller" text myself.

0.96" Button Display

Here is how to use this display with MiniDexed.

Raspberry Pi GPIO Connections

Display VCC	3V3	5V
Display SDA	GPIO 2 SDA	5V	DAC VIN
Display SCL	GPIO 3 SCL	GND	Display GND
	GPIO 4	GPIO 14 TXD
	GND	GPIO 15 RXD	Opt: MIDI IN
	GPIO 17	GPIO 18 PCM CLK	DAC BCK
	GPIO 27	GND
	GPIO 22	GPIO 23
	3V3	GPIO 24
Display K1	GPIO 10	GND
Display K2	GPIO 9	GPIO 25
Display K3	GPIO 11	GPIO 8
	GND	GPIO 7
	ID_SD	ID_SC
Display K4	GPIO 5	GND
	GPIO 6	GPIO 12
	GPIO 13	GND	DAC SCK / GND
DAC LRCK	GPIO 19 PCM FS	GPIO 16
	GPIO 26	GPIO 20
DAC GND	GND	GPIO 21 PCM DOUT	DAC DATA

As there are only four buttons, I'm mapping them to Next, Prev, Select and Back.

This is the minidexed.ini configuration.

SoundDevice=i2s

LCDEnabled=1
SSD1306LCDI2CAddress=0x3C
SSD1306LCDWidth=128
SSD1306LCDHeight=64
ButtonPinPrev=10
ButtonActionPrev=click
ButtonPinNext=9
ButtonActionNext=click
ButtonPinBack=5
ButtonActionBack=click
ButtonPinSelect=11
ButtonActionSelect=click
EncoderEnabled=0

The rotary encoder is on by default, so needs turning off.

Closing Thoughts

I was hoping to be able to get all three up and running, but although the third display is recognised and can be poked to some degree, at the moment it is just showing a garbled output. I suspect it will need some alternative mappings or something.

It was nice to see that the ssd1315 just worked as is.

I notice that MT32-Pi has support for SH1106 and it seems like a relatively thin layer on top of the core SSD1306 support, so I'll take a look and see if I can get this into circle in a useful way. It would certainly be nice to be able to add support for more displays in MiniDexed.

Kevin