How to Design a PCB for VHS Tape Case Synthesiser.

This article is more about design thinking rather than PCB manufacturing, but I hope it will help someone.

Step 1: Backstory. Why VHS Tape?

Last winter I've decided to get back to electronic music after a long pause.

And I came across the classical approach to sound generation with modular synthesis. I found the VCV RACK app where you could try modular synthesis in a virtual environment.

I was very excited about the possibilities of modular synthesis and wanted to try something less virtual. But there was the downside for the offline synthesizers — the price. Most of the modules are quite expensive.

Luckily there are some synthesizer producers like Bastl-Instruments who dig open source. Guys from Bastle make a micro modular synthesizer "Kastle" and provide all the schematics and source code. I liked how it sounded, so I've decided to give it a go. Besides for quite a while, I wanted to learn how to solder and build Arduino projects.

So for two months I was studying schematics and buying everything from BOM for Kastle. I wasn't planning to make a PCB for my first try in an electric project and chose to use a prototyping PCB.

Eventually, everything worked out. I've soldered everything and learned how to flash the firmware to Attiny 85. The resulting device was quite weak in terms of construction, but it worked for a while. When it eventually broke I've decided to make a better version.

I've spent some time thinking about what case I should use and what I didn't like in my first build. Original Kastl synth is a cool looking synth and is very portable. It is not that bigger of a tennis ball ) Check this promo video:

But this design makes it hard to patch oscillator parameters and turn potentiometers because everything is cramped on the front side.

When I saw someone throwing away a VHS tape it was BINGO! moment.

It was a perfect case for my new build: it is easy to find, easy to disassemble, plenty of space inside, some cool looking transparent `, hinged cover on the back to cover input/output and USB sockets.

All these benefits led to an idea to redesign the synth radically.

I came up with this design.

I've decided to separate the patch matrix from potentiometers. I didn't want any part protruding outside the tape case so I could use regular VHS sleeves. And when another person asked me "will it be a synthesizer with keys?" I've added a keyboard as a feature.

So the only problem with this build was that I didn't know how to make a PCB. I knew a year or so later I would figure everything out. But I got lucky and in July I've met an engineer who agreed to help me. I didn't expect at the moment that it will turn into partnership later.

End of backstory and back to PCB designing part.

Step 2: How Device Features and Product Design Affect the PCB Design .

The task seemed straightforward — get the CAD model of VHS tape, get the inner shape of the tape and design a PCB within this shape. But there are design features to keep in mind.

Let me list the features I had in mind:

Nothing protrudes outside the case
A patch matrix is hidden beneath the reel window
Input and output sockets are hidden behind the back cover
Potentiometers in the middle
Use accumulator battery for portability.
Make PCB modular if it's possible.

These features were crucial for PCB design.

We had to get the inner shape of VHS tape on a strictly calculated inner height.

To calculate it we've followed this math: PCB thickness + the height of the tallest element. In our case, it was a potentiometer. The rest of the components like push buttons and patch matrix position were defined by this height.

The rest was a technical redesigning initial schematic. Some features were added in comparison with original Kastle. The result was a project file we've sent to local PCB producer to make the first prototype of "Kasseta" synthesizer.

Another thing we've figured is that "Kasseta" PCB shape can be used for prototyping PCB that will fit inside VHS tape for other projects. So we've designed and produced it too.

Well That's It. I Hope It Was Useful.