First of all, much to my surprise, the layout for a reproduction SCELBI keyboard interface is nearly complete, well ahead of schedule. I’m not sure when I’ll pull the trigger on getting boards made, as I think it really needs to be used in conjunction with the oscilloscope interface or something similar.
Using the interface with many vintage keyboards may present a bit of a problem, as it was designed to interface with the keyboard design in the April 1974 issue of Popular Electronics magazine. The basic interface design is described in the first SCELBI Computer Digest, which can be found at Cameron Cooper’s scelbi.com website. The PE keyboard is unusual, in that it is ASCII decoded, but does not latch data. This means that data is only present while a key is actually pressed, or shortly thereafter (the keyboard circuit has a RC network that will hold data for a little while). This is why the SCELBI keyboard interface has latches incorporated into it.
Since there is no latching of data on the PE keyboard, the actual latch mechanism on the SCELBI interface is triggered whenever data is actively being sent by the keyboard. This will not work with keyboards that have onboard latches, since they present data to the interface all the time. Some kind of modification with have to be made for interfacing with those kinds of keyboards. This is not a huge problem, but will require some additional thought.
Of course, a more interesting solution would be to build a reproduction PE style keyboard to go with this interface. I couldn’t entirely rule out the possibility of taking on that project sometime in the future, but first I’m going to finish the few remaining SCELBI boards that are begging to be built.
If you did go down the route of designing a new keyboard would it worth making it a sort of generic keyboard that could be configured for use not only on the SCELBI but also Apple 1 reproductions? There seems to be a shortage of suitable keyboards.
Maybe – I have an Apple 1/Apple II datanetics style keyboard partly designed, but on hold. One (of many) reasons it’s on hold is that Wendell Sander already has a prototype of that style keyboard working. I believe that he is thinking of making a batch of them.
The PE keyboard uses mostly discrete components, so is not that adaptable. I think a daughter card could be designed that makes it more generic. I’ve spent all of 10 minutes thinking about this, but I expect there would be some interest for a PE reproduction or replica, if it could be made at low enough cost.
The Cherry KB that Tektronix used in the 4010 is ASCII and not latched. At one time they were fairly easy to find. I guess not any more. Anyway, it uses a neat, simple circuit, fully documented on bitsavers. I use mine unlatched, interfaced to an IMSAI through a Processor Tech 3P+S. It rarely drops a keystroke.