[KVM switch circuit / Multi-pole double throw switch]

The 157 is not a bidirectional switch

I had begun to wonder about that. In which case the video portion of the circuit would presumably work (two inputs, only one selected to output) while the keyboard and mouse would not (one input to one of two outputs).

I'm by no means restricted to using 157 chips. Getting parts is not a problem -- finding designs are.

[KVM switch circuit / Multi-pole double throw switch]

I've been searching internet, using all manner of phrases to find a circuit diagram for what should be a pretty simple project. What I'm hoping to build is a KVM (Keyboard / Video / Mouse) switch circuit for my computer.

A single keyboard, monitor, and mouse plug into the circuit, and the circuit is connected to the corresponding ports of two separate computer towers. Normally computer #1 sends/recieves the input/output to the peripherals. Flip a single switch, and the inputs/outputs are directed to computer #2.

In essence, a multiple-pole, double-throw switch.

I have asked around, and been told that multiplexing ICs are the key. I have several DM74ALS157 ICs on hand, and have attempted to build a simple circuit toggling between two LEDs using the attached diagram, but I've been unable to get a reaction out of it.

My electronics knowledge is sporadic; I can follow along in some technical discussions, and while I might not always understand how something works, I have no trouble following diagrams.