Keyboard change-over switch: If you have a non-qwerty board and would like to use this with your computer without having to relearn where the deviating keys are, this simple circuit will help. It receives two keyboards on K2 and K3 respectively and connects these via switch S1 and connector K1 to the computer. Check the keyboard connections on your computer, because some PC compatibles have a slightly different pin layout. The connection between the circuit and the computer is via a standard 5-way DIN cable; you can, of course, make your own cable as shown at the bottom of the diagram (K4 and K5).
Switch S1 is a four-pole change-over tYP e9 either rotary or toggle. Since the supply line is switched also, the additional keyboard does not increase the load. The additional LEDs that indicate which keyboard is in circuit increase the current drain by about 10 mA.
So much for the hardware; now for the software. Whatever keyboard you connect, the codes it generates do not change. Advising the computer that a different keyboard layout is used is the task of the keyboard driver. In MS-DOS versions up to 3.2, this driver is called KEYB??.COM, where in place of the question marks an abbreviation for the relevant country is given. Normally, the correct version of this program is executed in AUTOEXEr C.BAT, after the change-over you have to start the program manually. From version 3.3 onwards, there is the file KEYBOARD.SYS (and in some old versions), KEYB??.SYS), and then you have no choice but to restart (alt-ctrl-del) the computer every time the keyboard has been changed with a system disk in drive A on which you have stored the relevant data in CONF1G.SYS and pass these to KEYBOARD.Sys. Alternatively, you can i+tstall the Correct KEYB??.SYS.
