I've used my modular Raspberry Pi 2,3,4 A+/B+ Synth Case to create a variant for the two versions of my RPi Zero MiniDexed IO Board PCB Design.
The OpenSCAD file should allow for a range of variants to be produced, but I've gone for the following:
- HD44780 PCB for Raspberry Pi 4
- SSD1306 PCB for Raspberry Pi 2B+, 3B+
- SSD1306 PCB for Raspberry Pi 3A+
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, see the Getting Started pages.
OpenSCAD Design
This uses the core Raspberry Pi Case OpenSCAD module, but includes the details for the additional PCBs.
One thing I had to watch out for - the HD44780 version actually extends the whole box quite significantly past the end of the RPi, so this meant the following:
- I needed a way to extend the PCB and case within the original RPi module.
- I needed an option to not include a SD card cutout (as it would now be in the middle of the bottom panel).
- I had to support some components on the underside of the addon board that might extend past the original RPi circuit board (in my case the three MIDI DIN sockets).
This proved a little tricky, but I've managed to update the original module to allow the above.
The box height is now governed by the following:
- Thickness of the box - top and bottom (th).
- Padding around the Pi PCB in the z direction (pad.z).
- Thickness of the Pi PCB (board.z)
- Gap between the Pi PCB and the addon PCB (md_pad.z).
- Thickness of the addon PCB (md_board.z).
- Additional padding above the addon PCB (md_ext.z).
The md_ext parameter also allows the box to be extended in the x-direction (past the SD card) and y-direction (past the GPIO connector).
The addon board components are defined in a similar manner to the original RPi board definitions. There is a 4-element array detailing the original x,y,z position (with respect to the addon board itself), the original x,y,z dimensions, and then additional position and size parameters for the cutout for the component.
I've had to be somewhat conservative with the overall height of the box, aiming for something that is tall enough to encompass all components, but not so tall that the switch on the encoder won't work!
In terms of the SSD1306 this means that the MIDI socket pokes out of the top slightly.
There is one additional "hack" for the HD44780 version. I've added two additional PCB supports to the base that reach up to the addon PCB. For some reason, I've not been able to calculate the height. They should be pad.z+board.z+md_pad.z, when assuming they start at the thickness of the outer box. But for some reason I always come up short. So I've just hacked on an additional 1mm.
Find it on GitHub here.
SSD1306 Build
Some decisions have to be made about the PCB when it is constructed. Namely, the OLED display will require extending somehow to meet the display. It may be that simply using a pin header socket raises the display enough. Some experimentation will be required.
It will also be necessary to extend the buttons up to meet the case. I estimate a 12mm button would do it, but some experimentation is required here too.
In my case I 3D printed a couple of extensions to use, which has the added advantage that the buttons will match the case.
Also required are some M2.5 12mm spacers (and nuts/washers to adjust) between the boards.
HD44780 Build
As already mentioned, I had to strike a balance between having a box tall enough to allow all the components to fit, but not so tall that the encoder didn't poke through enough.
In the end my compromise was as follows:
- Use a pin header socket for the HD44780 display.
- Remove the plastic spacers from he HD44680 pins.
- Trim the pins down slightly.
This can be seen below.
Two sets of spacers are required:
- 15mm between RPi and the IO board.
- 10mm between the IO board and the display.
As the display headers have been slightly shortened, it may be necessary to adjust the retaining lugs on the rear of the display so that they avoid the optoisolator. This was only an issue for me as the optoisolator was in a DIP socket, so was a little higher than the other components.
Closing Thoughts
These PCBs weren't particularly designed with a case in mind, and it has proved a little tricky to get something that seems to work.
The HD44780 is much more suited to a case like this, and it shows, but I think both are relatively credible options really.
Kevin
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