(I am an IBM newb)
Few questions :
What exactly does the solenoid in IBM beam spring keyboards do? Am I right in saying it just makes a clicky noise?
Is there anywhere I can hear what it sounds like?
Is there any delay between the noise from the solenoid and the keypress?
Do all IBM beam spring keyboards have solenoids?
Thanks for the heads-up on this one, CPT!
Here's a short writeup I made:
A solenoid is a moveable metal bit surrounded by copper coils. You put current down the coils and the metal moves. You can use them in hydraulic valves, etc.
KB solenoids (for Wang, IBM, televideo, etc.) have a "stop" at the end and a spring. The spring holds the metal piece on one side. When current is applied, it hits the stop, making a click. When current is gone, it slides back into rest position with the spring.
They are used to make a keyclick sound in the days before DC buzzers and cheap piezoelectric speakers. You could also use them to ring the terminal bell, but in KBs they mostly are used to make a keyclick, as even the click of a beam spring wasn't enough for some typists raised on typewriters.
It's sometimes possible to cycle them fast enough to make them "buzz" but a lot of them can't really cycle fast enough for that. They might be able to handle a buzz (depending on frequency of course) but they are really designed to just make a click.
In short: they make the KB sound and feel more like a typewriter, which is what people were used to at the time. You can use them for other things though, too.
If you like, I can record my 3278 beam spring which has a working solenoid, but I'll have to put the keycaps back on.
There is a very slight delay, but it's almost imperceptible. The solenoid driver xwhatsit has puts a lot of current into it, which means it can accelerate the metal rod pretty quick. More current would make it even faster, but would require more power than USB wants to give it. The way it is now is pretty quick.
Unfortunately, the "reset" time that it takes the solenoid spring to push the rod back to rest position can take a little bit> If you hold a key down, it will build up a buffer of clicks. This could be fixed with a different solenoid and a stronger spring as well as more current to overcome the spring force.
Not all Beam springs have them: for example the displaywriter does not. Those 60% beams that are built into desks probably don't either but I don't know for sure. All the common ones do, to my knowledge. The IBM 3178 "model C" type of model F keyboards also have a solenoid in them.
