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SCK Data Board Failure

I have been doing rather a lot of work in developing firmware for SCS V3 to support several new sensors and I2C Mux.
This has involved debugging firmware and frequent installation of new firmware.
Inevitable lock ups has involved sometimes need to power up/power down the system; which is powered (a) by connection of 5V from a large battery to the power distribution and (b) connection from MacBook USB to the target device: data board MCU by USB cable. And I power down the system when I am not working on it.

So yesterday I found what seemed to be a failure of the Macbook to recognise the SCK device when its plugged into the USB port.
I got onto Apple Support; and we went through a process to see whats happening: he was very diligent.
It turned out the problem was not the USB on the MAC, but rather the device that it was plugged into: eg the Data Board MCU. (It was dead.)
Today I went about the process of isolating whether its the cable or the board. Pretty quickly I established it was the latter.
When USB cable plugged i to the device and then int the MAC; no LED’s lit up on the MCU board. Confirmation of the diagnosis.

Luckily I had replacement on hand; and I was able to replace the board. And now it is working again with the loss of a days productivity.

I have no way to establish just what failed on the Data Board : just to say that it does not work with power supplied by USB OR from Aux Grove connector. (I recall the John Cleese ‘dead parrot’ sketch from Monty Python at this point.).

The act of powering up and powering down this system under current circumstances is fraught with issues. With power coming from two sources I have no way to apply power at the same time from both sources (because I lack enough arms and hands to make plug-ins).
Power on the Aux Grove bus actually derives from the Spark-fun NEO M8U device; which has a fairly strong 5V > 3.3 V that (luckily) survives short term overload conditions when it is asked to power the entire system. It is specified at ~300 mA I think but the load is measured at about 380 mA @ 5V by the INA device. So the system needs the extra power that comes from the Data Board 5V > 3.3V conversion, so the two PSU’s run effectively in parallel.

I dream of the day when we have a different power supply arrangement for SCS; and have proposed distribution of power through Grove System. It is viable; but then I need a 5V>3.3 V convertor that can provide a load of at least 2 amps to cover all eventualities. (I am still looking for such a thing: none that I have seen have provision for Grove connection) This would avoid the need for multiple USB cables inside the enclosure; and they are unwieldy. The USB connections then be reserved only for programming and debugging.