One thing that was a bit of a pain with converting this board was the lack of diodes and the fact the shift keys were on the same columns as several alphanumeric keys.
My other FLS 3rd gen board has diodes for each switch:
- Another FLS 3rd gen board
- switches2.jpg (289.05 KiB) Viewed 4973 times
The
Tandy 1000 doesn't:
- Tandy 1000
- PBB_front_sm.jpg (264.58 KiB) Viewed 4973 times
I guess the original IC handled this, but since I just wired up the bare matrix, it caused problems with simultaneous key presses on the same column. I don't use my boards for gaming so I don't get hung up on NKRO, but I do like to be able to type a capital "C" with either shift key. So I wired diodes to the shift keys and the alphanumeric keys on the shift key columns - a bit of a pain because each switch has four contacts. Three of these are continuous with each other representing one switch terminal, the fourth representing the second terminal of the switch. On some switches the three represent the row terminal and the fourth the column terminal, but on others it's the other way around - and PCB traces often run though the contacts.
- contacts_labeled3.jpg (122.93 KiB) Viewed 4973 times
So as much as I don't like messing with original PCBs too much, I did some trace cutting and bridging and added diodes to the shift keys and the alphanumeric keys on those columns (and wired up the Caps Lock and Num Lock LEDs):
- Diode on Left Shift key (black and white wires to Caps Lock LED)
- diodes8_labeled.jpg (294.09 KiB) Viewed 4973 times
- Alphanumeric key on Shift key column
- diodes5a_sm_labeled.jpg (153.71 KiB) Viewed 4973 times
Kind of messy, but it works.
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