Hi,

I have a 16F628 based circuit that is used to monitor the water level, and
then operate a 240 volts, 3phase pump depending on the level conditions.

The software logic seems all right, and the unit works the way it is
supposed to. But, at times (about once a week) it behaves erratically.

Since the installation site is quite remote, I have not been able to
determine what the status is when the circuit misbehaves (as in, whether the
PIC has hung, or whether at this point it is not responding to the inputs).
The only way out in this situation is to reset the unit. I have simulated
all possible combinations of the inputs, and they work flawlessly, ruling
out a logic issue.

I've disabled MCLR, yet connected it to +5 to eliminate erratic resets.

Incidentally, the power supply is derived from a 480 volts transformer, with
the primary between 2 phases; this is because there is often no neutral
brought in into the pump house.The secondary has the usual full wave
rectifier, a filter (470 uF) followed by a 7805 and a decoupling 0.1 uF.

First, does this problem look power supply related? (I suspect it is)

If it is, what could be a cure? A more elaborate design with a Pi filter,
perhaps?

Or could it be anything else I am overlooking?

Please HELP!

Regards,

Anand Dhuru

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