The Port MuxR: A KVM switch for electronics

The Port MuxR
The Port MuxR

If you are a hardware/testing engineer, hobbyist or developer then you must be frustrated with swapping probes and cables on your device under test. And also wished to have something like KVM (Keyboard Video Mouse) switch for your collection of different electronics tools, devices, and sensors.

Do you have complex switching automation requirements and just can’t find the right tool? Or you just don’t know what you need, but want something useful in your electronics arsenal anyway?

The team of expert engineers and designers at SensorDots has developed a port switching design which switched the programming and test pins on different boards, so it could serially program and test each board with a single button click.

Introducing “The Port MuxR”, a bi-directional, 8/16 channel, switched bus multiplexer which works with either analog or digital signaling.

Unlike the other KVM switches in the market, it doesn’t just split out programming cables, it works for an array of 0-5V signaling levels.

Its working is very easy. It simply connects a set of pins, to your choice of additional pins on different switchable ports. These ports are all connected to a shared bus and tied together with a simple control interface.

Hardware Construction:

It comes with control circuitry that enables you to connect a collection of pins with groups of low resistance FET switches to a common bus.

The block diagram for the Port MuxR
The block diagram for the Port MuxR

A common primary port connection on the bus typically used for connecting a master device or programmer. Additionally, each switchable port has two groups of 4 individual FET switches. This gives you up to 16 x 4-pin channels or 8 x 8-pin channels.

In addition, the Port MuxR has a switchable Vcc line per port as well, which allows you to power devices and sensors from a 5/3.3V supply or optional external supply.

If we talk about its size, The Port MuxR board itself and the adapter boards are 4.90 x 2.00 inches (124.5 x 50.9 mm).

Moreover, there is a low V forward diode in series with the 3.3/5V supply lines to protect from any reverse current from devices connected to the boards. The Vf value depends on the current, but the drop is typically 0.1V@0.01A, 0.2V@0.1A, 0.3V@1A. To overcome this Vf drop, you can use your own supply on the PWR jumper connector instead. The 3.3/5V supply lines support up to 1A of supply current shared across all ports.


Besides, the Port MuxR is an easy to use USB serial or I2C control interface. The USB serial interface is great for interfacing with a PC and automation software, or if you just want manual control.

Also, the I2C interface is handy enough if you want to develop an all-in-one hardware solution, that utilizes the MuxR.

For users convenience, the team has also added an open-source, automation software toolkit that works directly with the serial interface. Using this software, you can also chain together or interface with multiple Port MuxRs, to increase the number of output ports you have. It even allows you to run commands after switching each port.

pplication: Port MuxR With AVR ISCP Adapter
Application: Port MuxR With AVR ISCP Adapter

And this is not the end, the team has created some additional application specific adapter boards, that allow you to connect up a few different programming cables. Also, EDA libraries are available to help you out.

The frequency response of the MuxR prototype under various conditions from 10kHz to 20MHz.

Frequency Response of Port MuxR Prototype (1Vpp @ 2.2pF)
Frequency Response of Port MuxR Prototype (1Vpp @ 2.2pF)

where, Attenuation = pin on, Off Isolation = pin off, Adjacent Channel Cross-talk = signal leakage to adjacent pin.

The Port MuxR has been designed with flexibility in mind from the start. Useful design files and sources will be released to make it easy to make modifications, as your requirements change in the future. The hardware itself has created to suit a multitude of different and flexible applications. This will make sure when one of your projects comes to a close, it can be re-purposed for another.