Friday, April 13, 2018

New Due Case

I recently picked up a nice little laser-cut case for my Arduino Due.  This one is by GeauxRobot.  They did a nice job on it including making little T-shaped button plastics to make the reset and erase buttons available.

This one does a nice job of supporting the ends of the board.  All the I/O connectors are nice and flush with the top of the case so shields can be handled as well as the SPI and JTAG connectors being accessible.



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Saturday, January 27, 2018

Optical Isolator

For some time now I have been chasing problems where I have multiple pieces of mains-powered equipment connected together via USB that for seemingly random reasons refuse to communicate.

Speculating that at least some of this behaviour is related the common ground through the USB cable and having separate power sources, I have built an optical isolator.

This incarnation takes 3V3 - 5V inputs and separates the power sources from each side.  There is only an optical signal connection between the sides.  The solution utilizes a 6N137 optical isolator.  I think in some circuits the amount of drive required may be problematic so version 2 will have a input buffer.  The output is inverted so a simple transistor (2N3096) inverter is used to set that right again.

So far so good, no "failure to communicate" issues have been seen with the isolation in place.  This particular board was already available from OSHPark thanks to Jason Pepas (http://github.com/pepaslabs) so all I had to do was build it.  My version has input output buffering, level conversion and an FTDI USB to UART chip.


Jason was kind enough to publish the gerbers, Kicad model and a PDF of the schematic.  He also did a nice write-up on his testing experiences.