Had a PIC fail

[Nigel Goodwin]

Well we all know how super reliable PIC's are, but I've just found one that's failed

It's a PIC 18F27K42 (my 18F PIC of choice) and among it's other jobs, it controls a switch-mode converter to charge it's Li-Ion battery pack.

As part of that it uses two analogue inputs, one monitoring the voltage, one measuring the current - and the I/O pin (A6) that monitors the current isn't working. As it monitors voltage and current, and adjusts the PWM for the converter accordingly, this wasn't good.

The current reading never changed from 0.002A, so the software kept turning it up (till it reached my MaxPWM limit), so the charging current was excessively high - but as the perceived current was below it's fully charged value, the software turned charging off as it thought it was fully charged. The software includes many safety features to shut down charging if there's a problem, and crude hardware features of a fuse feeding the battery, and also a fuse on the incoming 12V charging supply.

The charging current with a new PIC in is now happily 1.032A, and all is well.

 

[granddad]

I managed to kill a PIC18F57Q43 IO pin. they don't like feeling 12.5v . was just the pin, would not sink anything so I had some smd TQFP 48 soldering experience.( If you need 5, 8 bit + a 4 bit port its a nice chip).

 

[Nigel Goodwin]

I managed to kill a PIC18F57Q43 IO pin. they don't like feeling 12.5v . was just the pin, would not sink anything so I had some smd TQFP 48 soldering experience.( If you need 5, 8 bit + a 4 bit port its a nice chip).View attachment 147523

It was fed from the output of an opamp, used as a differential amplifier to monitor the battery charging current, they are rail to rail, fed from the same supply as the PIC.

I like DIL

 

[schmitt trigger]

We once had an Atmega failure on a critical subsystem for a heavy construction machinery.
The customer was the World’s largest heavy equipment maker manufacturer, and this was a top of the line machine.
As such, a deep dive FMA analysis was required.

To make a very long story short, a single BIT on the device RAM memory would randomly lose its state.