pythoncoder wrote:That USB tester is really neat: I could have done with one of those quite a few times. I was struck by this on their website
wonder what sort of voltage these things kick out? It's surely a violation of the USB standard carrying serious hazards. Do they pose a risk to the Pyboard and WiPy? From a quick look at the Pyboard schematic I'd say the answer was yes - via an overvoltage on pin PA9.
The device negotiates the voltage from the charger, up to 20V. You never get more than 5V unless the device goes through the procedure. I suppose if you did some tricky coding it might be possible to force it. But there is next to no risk to a pyboard.
For people using the low power modes a means of monitoring currents in the microamp range is required and I don't think those mentioned have sufficient resolution.
The chip has a 16 bit D to A and you can change the shunt resistor with the LTC6101, as well as adjust the gain with a high resistance divider. I'm planning on doing just that and comparing it do another reference once I get it running with the stock shunt. There will be some non linearity but I can deal with that in software.