After triple checking the schematics and design files and ordering 80 PCBs (50 sensors and 30 i2c boards) there was an anxious wait for them to arrive and do some initial tests to find out if there were any mistakes. We now have enough boards to make two new pattern matrix devices, one 4X4 and one 5X5 – the plan is to evaluate the design and refine it for future builds.
The picture below shows the first test boards populated and plugged it into the Pi – it’s much neater than the lego and breadboard prototype! The good news is that it seems to work so far, the only problem I’ve had is with the hall effect sensors, the pads are a tiny bit too close together for my skills. After a couple of tricky situations fixed with a de-soldering pump, I think I’ve come up with a strategy that works. I can bend the outer pins away from each other and solder the central pin first – then bend them back to finish the outer ones and being very careful not to bridge the pads.
The blue jumpers on the square i2c boards allow you to program the device channel that the two expanders use – these could alternatively be hard soldered, but it’s good to have the option to reuse the parts or reconfigure a pattern matrix so we can add different sensors etc.
For reference, the KiCad 3D viewer models look pretty close.
Never seen so many VGA ports, ironic perhaps. It’s great that it’s transparent, but I’m regretting the material choice for the panel – acrylic is horrible to work with and leaves behind lots of microplastics pollution I have to carefully collect up. Lesson learnt for next time, lots more soldering to do now – then more testing with the Raspberry Pi. Following on from the previous post, the instruction blocks will plug in to these 9 pin plugs.
Update after the last post. After many hours soldering 75% of the board is complete! The Pi can now address a whopping 12 bytes of data.
After thinking about it for a while, and checking with the languages I’m planning to use – I’ve decided to double the number of instruction ‘slots’ by halving the bits to 4. This doesn’t actually change the core hardware at all – I’ll just scan two at a time and split them in software (part of this project has been to see how much easier it is to change software than hardware). Some of the instructions can span two addresses if needed, but this makes more efficient use of the resources. The ports on the left of the board are where the plugs for the programming ‘interface’ will come in – each one will now split to two locations.
Here’s my test GPIO software running on the Pi, constant testing has been the only way to stay sane on this project. Eventually I could replace the Pi with a microcontroller for some applications, but the Pi has been a great way to ease the prototype process.