Electronic – Digital equivalent of a double-throw switch

It would be really helpful if you knew how the switch was wired within the KVM relative to the rest of the circuit to understand the best application of a transistor or IC.

For instance, if the switch is just bringing an input to ground through a resistor, you may be able to sink the current directly through an I/O line

In the absence of specific information on what the switch is doing, you can't go wrong with replacing a switch with a relay. The relay contacts would replace the switch, and you would drive the coil from the Arduino through a transistor (since the I/O line can't drive the relay directly). Of course, you would have to deal with the clicking and the relatively shorter operational life of a relay over a transistor.

USB Micro has the following lines:

• VBUS (+5v)
• Data+
• Data-
• ID
• Ground

Of these, ID is generally not carried over a cable: It is either shorted to signal ground (host device) or left open (slave device). It does not carry any data.

Both VBus and Ground can be left connected to both endpoints in the scheme, thus reducing the switching requirement to 2 lines, D+ and D-. (Another line for ID if it must be carried across, but never seen that done). This is why USB multiplexer ICs typically carry just 2 channels.

There are several USB 2.0 multiplexer ICs that would do the job, for instance Intersil ISL54200, Maxim MAX4906/4907, or Texas Instruments TS3USB221E.

A TTL-controlled bidirectional analog multiplexer/demultiplexer like the HC4053 may be less expensive but will not work for this purpose, due to data speed requirements and capacitance matching issues.

As noted by others in the comments, USB does not take kindly to endpoints being switched. The USB protocol is not a basic TTL logic connection, it involves identification of the USB device and negotiation of speed (and also current limits). Until this handshake is done, the connection is not done.