Since i'll be manufacturing a bigger batch of the USBpwrME all units needs to be tested before sent out to customers.  Of course I built a test jig that tests all functions with as little interactions as possible. Making a test jig is actually more complicated than one might first imagine. Connecting the DUT with banana connectors to input power and then connecting the USB connectors for readout and manipulation of the DUT gives some challenges both with creating a hardware that work in parallel with the DUT but also writing firmware to cover all test scenarios. 

Thera are 2 "major" mistakes i did when designing the test jig. The first one and was easy to fix.  I use three relays for switching things on the USB connectors. But when implementing the firmware i could not get the relays to switch. Looking at the schematic i noticed in the symbol that the coil is actually polarized for this specific relay. Doublechecked the datasheet and yes, i needed to modify the board and swap +-. Easy fix that could have been avoided.

The second issue is hard to predict and cannot be fixed in good way more than with the implemented test sequences. 

On the USBpwrME there is a wrong polarity input protection that i test by inverting the input power thru a relay and check that it shuts of. What i did not predict that the GND of the DUT is connected to the GND of the test jig not only by the input to the DUT but also by the GND  shield och the USB connectors. So when i invert the input power to the DUT i actually short-circuit the power of the test jig du to the USB connection. This can be solved in hardware but i added a step in the test sequence to not connect the USB cables until this test is performed. It adds some testing time but it works! 

Following test sequence is implemented in Firmware. The green boxes are automated test steps while the purple boxes are action required by tester. After a failed test each ADC value presented on the display and the E..x error code to make it easier to trouble shoot.