Two Keyboards on one PC

This circuit does the exact opposite of what most of this type of changeover switches attempt to do. Usually a changeover switch is used with two PCs and one keyboard. This version however makes it possible to operate one PC with two keyboards. K1 is connected to the PC for this purpose while K2 and K3 are connected to two keyboards.The data outputs of the keyboards are high in the idle state. As soon as a key is pressed the keyboard will serially transmit the data. The data line will now also be low from time to time. This low level is detected and remembered by the flip-flop circuit around IC1.