nascom1_keyboard

The Nascom-1 was only expected to sell about 200 kits. They bought these rather nice keyboards from a company as surplus items, which were originally intended to go into computer terminals but were never used. Later kits had more conventional keyboards.

The keys available are pretty minimal. The Reset key (not shown on the above keyboard) was a standard switch which had to be soldered to the board. You can just see the 2 holes for it close to the top edge of the PCB, above the 2 blank positions at the RHS of the top row.

Pressing keys is all well and good, but in this case it’s interesting to see how they work. As far as I know there are no longer any magnetic-transformer keys made by any manufacturer.

key-bottom

Construction of these Licon keys is interesting. There is a central core on which there are 2 windings, primary & secondary. These are of very low resistance. On two sides of the core there are magnets, coupled to the shaft of the key and sprung upwards so that they are on each side of the coils. The magnetic field saturates the core so that pulses are not passed through the transformer. When the key is pressed the magnets are moved downwards, away from the core, allowing the scanning pulses to pass through.

key-releasedkey-pressed

 

 

Pulses are sent to columns of keys (the computer sends “counter reset” and “clock” signals) and the rows read back via the keyboard matrix. Any pulses picked up are then latched and the contents of the latch read back by the computer as a 6-bit code. That code is then decoded by the monitor software.

ct1keyb

Keyboard circuit diagram