So, you got one of those TI99 keyboards from Radio Shack for $2.95 and still have not wired it up to your 1000 or 2068, right? I was going to write this up a while ago, but I learned that so many different companies made the circuit boards that it would be difficult to give a direct “how to” and cover all of the permutations. The response in favor of the article was overwhelming, so here it is.
It is not necessary to grind off all of board traces and rewire the entire board. It is necessary to make a number of trace cuts though. All of my keyboards have numbered pads on the underside. Since each key is actually a switch, there are two pads for each key. These are denoted as left and right in this project.
A key matrix schematic comes with your keyboard. Mine has the keypads of the numbers 1 through 0 labeled as 1 through 10. A is 23 and V is 38. If yours is numbered the same, then you should have little trouble wiring your keyboard as described herein.
Only the bottom row needs to be cut and moved over one. Fortunately, the TI and ZX matrix are similar. A few of the special keys must also be jumpered around, and the space keys must be linked up again too. Cut the traces above or below the pads specified. Then jumper the necessary pads together.
Cut as follows:
ABOVE BELOW
46L 44R
47L 39L
33L 38L
33R 12R
42R 26R
41L
41R
40R JUMPER TO
37R
36R 33L 10L
35R 33R 31L
34R 40R 30R&26R
32R 38R 27R
22R 37R 26R
36R 25R
35R 24R
34R 35L&44R
39L 40L
12R 23L
26R 15R
I refer you to Volume 1 of SWN, page 42, and/or the ZX81 or 2068 schematic for the ZX key matrix. You may now directly solder or otherwise connect the ribbon connector of the keyboard to the computer as follows:
KEYBOARD COMPUTER Pin 1 D5 Pin 2 D3 Pin 3 D4 Pin 4 D7 Pin 5 D8 Pin 7 D1 Pin 8 K0 Pin 9 K4 Pin 10 D2 Pin 11 D6 Pin 13 K1 Pin 14 K2 Pin 15 K3