Sunday, 10 August 2014

Raspberry Pi B+ ZX Spectrum USB Keyboard Case Mod

When I reviewed the Raspberry Pi Model B+ last month I knew it was going to make some changes to the way I integrate the Pi into my retro computer USB keyboards. Once I've made the old computer into a USB keyboard, the next step is to integrate the Raspberry Pi . I could just throw the Pi inside and trail the wires out of the computer. But that would be too easy, and a bit impractical. What I like to do is to arrange the connectors into the spaces where the original connectors were, so it appears like a finished product.
The wires are all then plug neatly into the back and away you go.
The problem is, due the space limitations inside a small case like the Spectrum, this means quite a lot of work to reduce the height of the Pi, and align the connectors. One of the big problems with the older Model B boards is the USB and LAN connectors don't line up, so couldn't be placed together on the back of the case.
Also the Model B has only two USB ports usually led to the USB jack being removed and connected to a four port USB hub (which fitted neatly in the expansion port). The other USB connecting to the keyboard controller.
This just about fitted into the Spectrum case, with a choice of external connectors. Either the LAN as above, or the SD Card.
Or Composite Video and Audio if you like.
On the new Raspberry Pi Model B+, the USB ports have multiplied and fallen back into line with the LAN jack, so it is now possible to use those unchanged.
The Commodore 64 above fits very nicely, but the Spectrum needs a little creative dremmeling to the case.
The HDMI and power still have to be extended to reach, but the inside is a lot simpler.
With a little planning, that has left space for the USB keyboard controller in the top of the case. I've had to modify one of the ZX81 boards here as space is tight. I need to design a new USB keyboard PCB for the Spectrum now.
The end result is a fully integrated Pi
This one is also slightly different to normal as the customer has selected the loopback option. This means it can be used in two ways. In one way, it is a ZX Spectrum USB keyboard that can be plugged into a laptop etc. This utilises the micro USB output jack only.
The second mode uses a short cable to connect that to the Raspberry Pi B+, so the Pi can use the keyboard, it then becomes the complete Pi system.
This is also the first to feature an external switch for the keyboard mapping mode. Previously, this was only changeable via a jumper on board, but I've moved that to an external switch, just visible through the Mic hole.
This means the fully mapped keyboard, with access to various symbols and functions as printed on the keycaps, and more importantly function keys, can be used when running Raspian and setting up things like the Fuse spectrum emulator. Then the switch can be changed to the direct mode, where all the keys will work correctly in the emulator. I'll soon be making these versions available in my Etsy store. If you're interested please contact me.
Update: I've now added an RTC module.