I have few computers on my desk and to make chaos smaller for all of them I use only one keyboard connected to USB KVM switch. The original was cheap mechanical - based on a push button. Few months it was working fine, but some time before it started to make problems - the commutation was broken - I had to press and press again the button until it connects properly the keyboard to the desired computer. It is known the the weakest parts in electronics devices are always the mechanical parts. So... I decided to make fully electronic KVM USB switch.

I wanted to use the same housing of the old mechanical switch. Its extracted PCB is shown on the pictures. The new electronic one has to have the same dimensions and all USB connector have to be placed on the same positions. In this way the new PCB would fit directly in the old KVM case. For that purpose I measured precisely all the dimensions of the old PCB, whole holes coordinates and parts positions. All this was drawn on sheet of paper used after that a base for the new PCB design.

The main part of the electronic KVM USB switch is the Texas Instruments TS3USB221E High-Speed USB 2.0 (480Mbps) 1:2 Multiplexer – Demultiplexer Switch Chip. (The datasheet is attached). That solved the problem with the 2:1 Multiplexing. Now was sought a solution how to omit the mechanical switch. Instead it I decided to use touch sensor. I chose the TTP223 module. It can be found almost in all electronics online shops. Its advantage is that it has programming solder bridges, which can define its working mode. I needed to force it in triggering mode - one touch on, next off...and etc. For that purpose the bridge B have to shorted. Because the TI chip TS3USB221E works on 3.3V supply, which is also accepted by the TTP223 I added a 3.3V Voltage regulator with AMS1117-3.3V with all needed surrounding caps. The TTP223 controls which USB connector is passed to the output one. On its output I put also both LEDS indicating the active USB channel. The power supply USB lines from the computers sides are separated by use of Schottky diodes ( PMEG3050EP - 5A, low voltage drop).

All the information about the project can be found here : https://www.instructables.com/Electronic-KVM-USB-Switch-for-PC-Keyboard/