2026-04-16 Test Jig for USBpwrME
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.
2026-03-10 USBpwrME prelaunched
So it's time to run antoher crowdfunding campaign! It's prelaunched and now it's time for social media work for increased visibility.
USBpwrME should be e great campaign but time will tell.
Everytime i need to power up some usb connected gadget in a controlled way with a power box i have issues finding cables that fits the purpose. And when i have finally found it, i need to cut it so it can connected to the power supply banana connector. When the job is done of course i throw away the cable. And nextt time i do it again and again! :( :)
Well that is how i came up with this project. A simple adaptor with one USB-C and one USB-A connector to make it backward compatible.
The first prototype was a bit to simple and dirty. I had only polarity protection and a couple of resistors on cc1 and cc2 pins to enable the USB-C Vbus voltage and the 2 connectors.
Yea that didn't quite work at all as intended!
So going forward i decided to think thru what i want to achieve and how to do.
I decided on following requirements.
-Input voltage 3-20V
-Current capability 6A total
-OVP, over voltage protection
-Wrong polarity protection
-Charging negotiation at 5V
-OVP protection manually controlled if needed.
-Fit most power supplies in terms of binding post distance.
The schematic is fairly simple and i really wanted to avoid to use a MCU to make it easy if i decided to make some kind of product of it.
Ill try to go thru the block of the schematic and try to explain on how it works.. in i higher level.
"Input block"
The input block is really simple and is basically made up by Q1 which is used for reverse polarity protection and a LDO with 5V output to power the internal circuits on the boards.
"OVP block"
A simple low cost OP connected as comparator that enables the load switch Q8 to supply the USB-A and USB-C Vbus. This is if the input voltage is below 5.6-5.7V. When above there will be no output voltage to protect the DUT.
The switch S1 will ground the input of the comparator and forcing the output to enable the load switch. This disables the OVP and pass thru voltage.
Vbus for USB-C is not on by default and is controlled by U2. Therefore to also force Vbus high the switch also controls Q2 regardless what is negotiated on Vbus C.
When OVP is disabled the orange LED D8 is turned ON to notify user that OVP is not active!
"USB-A negotiation"
Vbus for USB-A is always enabled according to the standard and the U4 IC basically tells the DUT that the maximum allowed charging current is 2A (10W)
"USB-C negotiation"
By default the Vbus for USB-C is disabled and is only enabled when a successful negotiation is performed with the DUT. This is entirely handled by U2 which also can allow up to 3A charging current (15W).
It was really hard to load the board in good way to be able to draw 6A. Connection gets easy warm and contact resistance makes a big impact on measurements.
Well anyway i did many tests to make sure that the board and components are within specification regarding max temperature. All in all there are god margins.
The TUSB319 chip handles the USB-C negotiation and it works fine. I verified all functions and voltages on pins with a attached and detached device. All pins work as they should but there is a pin that named DIR and is pulled up to 5V. As far as i understand it's a pin that shows the orientation of the inserted usb connector. It should change when inserting the connector. But for me it's always 5V. I have so far not figured out why. I'm not sure either what this pin is actually for more than as to be monitored by a external MCU or something.
I found a block diagram on TI homepage which i used for comparison.
Need to look more into it.
So i decided to try to manufacture a test batch of 10pcs at a factory to see if there are any issues with the layout. I expected some issues with soldering of the small chip U2. And yes there were some boards where this component is not correctly soldered.
What really surprised me was that 2 boards came with destroyed components and pcb, really disappointed and i'm in contact with the factory to get an answer on what happened. Not really hoping to much.
I'm planing to do some crowdfunding on this project and and the campaign is in pre launch stage so i guess there is time to improve production!
Since i'm planning to build a bigger batch of USBpwrMe i actually need to test each unit in a fast and repeatable way. Therefore i have designed a test jigg that will measure all functions.
Following steps will be performed
1 It will measure the current consumption of the board to see if there is excessive power consumption
2 It will change polarity on the DUT and measure if there is any voltage on the output.
3 It will will apply resistors on the D+ and D- lines och the USB-A connector and measure so that expected voltage appears.
4 It will apply resistors on the CC1 and CC2 line for the USB-C connector. Vbus1, Vbus2, CC1 and CC2 are measured. If negotiation is
correct it will enable Vbus.
5 It will change input voltage from 5V to 6V and test so that the OVP protection works.
6 Finally it will test the OVP mode switch by telling user to turn of OVP. And measures that Vbus goes on.
2026-03-01 ESD gun part II, upgrade
The ESD gun i built a year ago works really well except for one thing, it crashes a lot and needs to be restarted. The electrical fields internally in the gun disturbes the controller board and makes the MCU to hang or behave unpredictable. It cannot be determined how the interference actually reaches the MCU but i went for a extensive protection strategy and try to stop all disturbance paths!
The picture below shows how the ESD gun is built up as two different units to try to separate the "dirty" HV (high voltage) side from the sensitive side which is the controller board.
As seen, the gun has two GND areas which is more or less isolated from each other. GND area 1 is connected to the 24Vdc negative input as reference and GND area 2 is connected to what is considered as ground reference of the output high voltage side, this is also connected to the DUT GND reference.
The Faraday cage creates a shield against fields emitted out from the HV side and it shields fields against coming into the controller unit. For extra shielding the HV module has 2 Faraday cages for additional shielding.
The dotted barrier represents the border between the 2 units and i have tried to keep them separated by using chokes and inline ferrites on cables!
Started out with printing a whole new casing in black.
Step by step all inside was covered with adhesive copper foil to create the shielding box. Both the HV and the controller cavity was treated with same procedure! Also ferrite sheet was added to suppress high frequency disturbance coming from the HV module.
As mentioned the "negative" output from the HV module is connected to the shield box to set the reference plane inside the shield.
The cables between the two modules are run thru ferrite cores by a couple of windings. They are placed in a small cavity between the two modules. Doesn't look really great but it will do the job.
All signals are passed thru inline ferrite beads, even the signals considered as GND to try to separate disturbance from reaching the controller board. The ferrites have around 500 ohms @ 100MHz but of course can be considered as 0 ohm @ DC levels or low frequency signals.
Looks really clean and thought thru!
Since the wires (24V power and trigger signal) from the handle runs thru the HV module i made up a plan to try to keep thees shielded from the HV field so i created an additional internal shield box so int theory the cables should be quite safe. 3D printed a new internal box which was covered in copper foil and i made sure that it has god connection to the surrounding GND shield.
Finally a conductive cushion is connecting the lid to the internal plane to create a fully sealed shield box and also keep the things in place mechanically.
Since the improvements/ upgrade i have shot more than 200 shots with not one crash or symptom whatsoever so i can be quite confident that all the protective measures did really help and made the gun really stable and well working.
