One thing the CoCo community has needed for some time is a viable way to repair or replace the keyboards in our aging machines.
The original CoCo keyboard is a membrane type internally, with the circuit printed on mylar. Many of these mylars are wearing out today, and the conductor tends to develop cracks in the section connecting to the motherboard.
In the recent past, there has been talk of having a run of replacement mylars made, with a couple of individuals going as far as to get quotes. Though an option, prices seem to be expensive enough that to date this has not happened.
Cloud9 has developed a solution that involves a very thin PCB with tactile switches being used to replace the mylar in original keyboard casings which looks like a good option.
Having wanted to make a keyboard replacement myself for quite some time, I decided to throw my hat into the ring with my own design. I had a couple of criteria for the final keyboard.
- It had to use standard modern key switches of the current de facto standard
- It had to be a drop-in replacement
Later models of the CoCo1, as well as CoCo 2 models and the CoCo3, can all accommodate the same design. These are models I’ve targeted.
One of the major obstacles to a new keyboard for the CoCo is that like most early computers, the legends on the keycaps are not laid out as they are in what has become the standard layout over the years. This means that new keycaps that will fit modern key switches cannot be purchased with pre-labeled keys. Blank keycap sets are available, but then there is the issue of labeling them in a professional fashion.
Of course there are companies that will produce custom keycap sets for you, but prices and minimum quantities are high, and any change in design would be very expensive.
One of the ways manufacturers label keys is using lasers. After investigating this a bit, I decided that would be a good way for me to go. Owning the laser system myself would allow me a great deal of flexibility as well, enabling me to put nearly anything on nearly any keycap at a whim.
So I purchased a 20w fiber laser system for the purpose (and for other things).
20w fiber laser system
The system is quite flexible, and does the keycaps with ease.
Laser marked keys, an early test
Keycap marking with the laser
With a solution for the keys decided on, I moved on to the rest of the design. To avoid needing special molded or printed parts for a keyboard housing while still providing enough rigidity, I decided on a design that would sandwich aluminum bars between the switch PCB and a top plate (bezel) around the keys.
Initial PCB design
Another issue with a CoCo drop in keyboard is how to go about the connection to the motherboard. This I accomplished with a thin (.6mm) PCB for the main board connector and a ribbon cable. Receiving the PCBs back for the fabricator for all this, I proceeded to assemble a prototype.
PCBs for prototype keyboard
The keyboard is modeled after the original CoCo3 keyboard, shown with the prototype in the picture below.
Prototype with original CoCo3 keyboard
First test, CoCo MECH keyboard
Next I installed the aluminum frame, drilling and tapping the rails to fit the PCBs. I assembled this prototype in a hurry with hand tools. Things will be more precise in actual production, but still, this went well.
Prototype with frame installed
Prototype installed in a CoCo3
Installed in an ‘F’ board CoCo 1
I made some changes and produced a 2nd revision of the board which I’ll order to continue development with. This project has gone extremely well so far and I don’t see any issues in further refining it into a great drop in keyboard option for our CoCos!
REV02 design, main PCB