Remapping the HP150 keyboard

Many reasons. There isn't that much space inside the HP150 keyboard, I guess it could fit if I used SMD parts (but there may not be enough headroom for a socketed PLCC EPROM). It's a lot harder to prototype with SMD parts in my experience. I can wire up through-hole devices on stripboard in a couple of hours, testing as I go. If I used SMD, I'd have to lay out a PCB (takes a lot longer than running wires!), either etch it or more likely send the design off somewhere and get the board back a week later, and then I'd have to debug it, and repeat the PCB production when I'd found I'd made a mistake (rememebr that in this case I didn't have a documented interface I was connecting to, I had to make assumptions as to how the HP150/HP120 keyboard microcontroller behaved). And as I mentioned I did make a few modificuations while tracking down a problem which turned out to be a dodgy keyswitch on the HP150 keyboard. Doing that with SMD parts would have been a lot harder And if you think I can afford to prototype with through-hole and then make an SMD version, think again! At least not for a one-off like this. And of course, when doing mods like this I like to use components that were around at the time the machine was made, in packages that were currently used. SMD was not common at the time of the HP120/HP150. -tony