One the things I really wanted to pay attention to for my MiniDexed TX816 was the panel itself. Usually, my panels are a very “DIY, it’ll do” affair but I want this one to at least make an attempt to capture some of the style of the original TX816.
I looked at a range of options and in the end designed the panel as if it was a PCB and then looked at some quotes to get one made. Then I used https://pcbshopper.com/ and went with the cheapest.
This post looks at the design of the panel.
Posts in this series:
- Part 1: Introduction, context, and high-level design.
- Part 2: PCB design.
- Part 3: Panel design.
- Part 4: PCB assembly.
- Part 5: Mechanical assembly.
- Part 6: Pico MIDI Router and TX816 IO Code.
- Part 7: In use!
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High-level Sketch of the Panel Design
As mentioned previously, this is the general design I’m going for. It is a 250x160mm panel that will fit nicely as one of my CD Rack Synthesizer Projects.
I’m not going to go through all the specifics of the measurements here, but the basic principles are:
- The panel is the full 160mm wide.
- The top and bottom 20mm of the 250mm panel are reserved for fixing and mounting.
- For symmetry, I’ve left a 40mm gap in the middle between the two rows of tone generators.
- This gives me a single tone generator area of 85x40mm with 20mm spare top and bottom.
- The central 40mm strip is where I’m going to position the MiniDexed IO.
- There are no mounting points for the PCBs themselves, I’m hoping to rely on the fact that they will be anchored using four potentiometers each!
Whilst I’ve arranged this for two-rows of tone generators to fit into my CD Rack Format, there is no reason why the 85x40mm design couldn’t, in the future, be re-used in a different way – either for individual “tone generators” or as a single row of 8 tone generators.
It also really wouldn’t be much of a stretch to fit each one into a 4HP Eurorack module (128.5mm high; 1 HP = 5.08mm wide) if required. In fact I really like the idea of a Eurorack version at some point in the future and could probably re-use my IO PCBs too.
Here are some of my scribbled notes about the dimensions.
I used the KiCad PCB layout editor to design the panel:
- I started with the full board dimensions, picking a useful origin and defining the outline edge cut for the 250x160mm panel.
- Rectangles were produced using Edge Cut shapes and placed using absolute positioning.
- Most holes were placed using various sizes of “mounting hole”. I ended up using the following:
- 2mm – LEDs (I’m using “lighthouse” or “tower” style LEDs that have a 5mm footprint on the PCB, but just require a 2mm opening)
- 2.5mm – mounting holes for a 128×64 SSD1306 OLED display (I’m using this as it comes with mounting holes, unlike the 128×32 display I’d normally use).
- 3.5mm – panel fixing holes (top and bottom for mounting into the “rack”).
- 6mm – MIDI sockets (I’m using MIDI TRS, panel mounted sockets).
- 8mm – potentiometers, encoder, audio jack.
- Update: the potentiometers I ended up using actually required a 9mm diameter hole, so I had to widen these holes in the final build.
- The exception was the power switch hole, which had to be 12mm, so I used a 6mm radius circular edge cut.
- The front silkscreen was used for all labels.
- I added a copper ground plane front and back, even though I don’t plan to use it.
I saw some advice that to have a panel made from a PCB manufacturer, their automated systems might come unstuck if there was no copper layers.
Then after sending it off, I also read that a copper ground plane can help ground potentiometers and other panel mounted components. But this would have required some of the solder mask to leave some of the copper exposed, which I didn’t do! Maybe next time.
Here is the KiCad PCB view of my panel before filling in the ground plane zones, alongside the panel I got back from the PCB manufacturers.
This was ordered using all the default options apart from the PCB colour, which you can see was black. I just exported the Gerber files as usual and uploaded them to the manufacturer to get a quote.
Closing Thoughts
I investigated a number of avenues for making a panel, and all online, commercial operations would have turned out to be quite expensive compared to treating it as a PCB. As it was, many PCB manufacturers wanted a fair bit too, but using pcbshopper I just went with the cheapest and this was the result.
My other CD Rack panels are 2mm thick aluminium – this is just standard 1.6mm FR4. Whilst it is possible to specify 2.0mm FR4 it is a lot more expensive than the standard sizes. If it was just holes to be drilled, I’d have probably simply gone with a DIY aluminium panel as with previous builds, but that would have almost certainly meant giving up on the TX816 esthetic.
I’m really pleased with how it looks, so the crunch time will be if it stands up to any significant use once the PCBs are attached behind it. I’m also still wondering if I should have included some additional mount points between the PCBs and the Panel. There will be “spare” mount points on the PCB, so if it seems like more are required, I could always hand-drill some extra holes in the panel.
Another uncertainty is the “z-axis” component… I was really careful about the x-y placing of components on the PCB and mapping that across to the panels, but I really didn’t quite know how to model the gaps between the PCB and panel. In the end I opted not to worry about it and figured I’d try to work something out once I actually have the physical objects via some ad-hoc hacking about.
This is an area where some kind of quite turnaround 3D model would have been really useful!
It would be really handy to have a local maker space with a laser cutter and 3D printer… but then I also like being largely independent!
Kevin
Simple DIY Electronic Music Projects 