From the successful Kickstarter - https://www.kickstarter.com/projects/sensordots/sensordots-port-muxr-a-kvm-switch-but-for-electron

Have you ever been frustrated with swapping probes and cables on your device under test, or are you a hardware/testing engineer, hobbyist or developer that has had to create a test and measurement automation jig for an array of devices to program and test at once?

Ever wished that you had something like a KVM switch, but 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?

If you are looking to do any of the following:

• Branch out programming cables to multiple devices - to save yourself from buying multiple expensive programming cables and easily scale automated test jigs. Easily progress from development to production with the same programming hardware you have on hand.
• Multi-processor communications - e.g. connect multiple microcontrollers to the same sensor in a many to one arrangement.
• Test and measurement systems - simplify and automate your test and measurement environment.
• Automation control systems - e.g. integrate the MuxR into your control system design.
• Connecting up to multiple different sensors and devices for testing and debug - e.g. connecting to multiple sensors with the same hardware addresses.
• Joining buses together programmatically - e.g. I2C/SPI/USB.
• Testing different buses with a single test and measurement device, without having to switch probe cables around - e.g. logic analysers.
• Creating a KVM like switch for your embedded devices and peripherals - or even create a KVM for USB/PS2/Analog video.
• Education and visualisation - e.g. switch between different signals easily for demonstration purposes.
• Any bus or pin switching application you can think of.

Look no further and read on!

The Port MuxR

The Port MuxR is a bi-directional, 8/16 channel, switched bus multiplexer which works with either analog or digital signalling. So it doesn't just split out programming cables, it works for any array of 0-5V signalling levels.

Quite simply, it connects a set of pins, to your choice of additional pins on different switchable ports, which are all connected to a shared bus and tied together with a simple control interface.

The control circuitry allows you connect a collection of pins with groups of low resistance FET switches to a common bus. The boards also have a common primary port connection on the bus, which is typically used for connecting a master device/programmer (but you can connect up any port to any port as they are all linked via the bus; useful for one-to-many or many-to-one arrangements). Each switchable port has two groups of 4 individual FET switches, giving you up to 16x 4-pin channels, or 8x 8-pin channels.

There's also a switchable Vcc line per port as well, which allows you to power devices and sensors from a selectable 5/3.3V supply (or optional external supply).

Features

The Port MuxR features include:

• Bidirectional data flow, with near-zero propagation delay through each FET switch.
• Low ON-state resistance through switch ICs (Ron = 3 Ω typical, @ 3V) and optional series resistors on primary port pins.
• Low input/output capacitance.
• -2V undershoot protection prevents the FET (NMOS) switches from inadvertently turning on (when in off state) during signal undershoot events.
• 0 to 5V signaling levels supported.
• Supports both digital and some analog applications (see note above about -2V undershoot).
• 200MHz bandwidth through the MOSFET switches (attenuation and crosstalk begin to impede signal beyond this point, but higher bandwidth signals might be possible if they use differential pairs/are resistant to noise and attenuation). See here for signal measurement characteristics up to 100MHz.
• USB serial/I2C slave control interface with selectable I2C addressing (the I2C port is master mode capable too for extensibility in your own custom application).
• Low crosstalk through switches when off.
• 8 controllable Vcc pins (with LED indicator).
• 3.3/5V Vcc selection header (with optional external power on adapter boards).
• 8x8 pin or 16x4 pin multiplexing with additional primary port.
• Included open-source .NET based control software (builds under mono as well for Linux use).
• Open-source Arduino control firmware for easy updating or modification to suit your requirements (running on an ATmega328PB).
• Different port switching settings available. E.g. Port make-before-break, break-before-make, port grouping, manual toggle.

Software

Alongside the hardware, 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. The I2C interface is handy if you want to develop an all-in-one hardware solution, that utilises the MuxR. For example, you might like to create simple button interface hardware to control the switching instead.

Also included is 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 (e.g. running your programming software).

Adapter Boards

We have also created some application specific adapter boards, that allow you to connect up a few different programming cables. Different adapters can also be created easily and EDA libraries are available to help you out.

To start with we have created an AVR/Atmel 6/10 Pin ICSP Splitter as well as an ARM JTAG/J-Link (Segger) Splitter (shown in the gallery above).

Bits & Pieces

The boards currently have a white PCB, rather than the purple shown in the images.

Please note, the connectors on the adapter boards will arrive unsoldered. The main Port MuxR board is supplied without port connectors. However if you order an adapter board it will come with appropriate mating connectors for the Port MuxR board. You can solder these in any orientation you see fit (male header to female or vice versa) or swap them out with a longer style of header.

The mounting holes in the corners fit up to 3mm screws. Design files with the locations of these are available in the GitHub repo, along with pin layouts. The Port MuxR board itself and the adapter boards are 4.90 x 2.00 inches (124.5 x 50.9 mm).

There is also a low Vforward diode in series with the 3.3/5V supply lines and VCC output ports (see the block diagram above) to protect from any reverse current from devices connected to the boards or from an external supply. 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 (this is supported on the adapter boards), or you can bypass D9 by soldering a wire between the two through holes either side of it. The 3.3/5V supply lines support up to 500mA of supply current shared across all ports when powered from the USB port (and up to 1A from external supply). The board itself has a quiescent current of 20mA@5V through the USB port).