Mysterious Reset Revived!

[skimask]

The Questions:
Is there another circuit that i could attach to my cascade of doo dads? the relays and I/O mods all have snubbers built into them.
OR, can I run the PIC with the BOR disabled? I've read that i could be placing some of my volatile memory at risk, but how risky is it? in all the time i've run with the BOR disabled, there have been no problems with loosing variable values.
Is it just bad form to run the chip without the BOR?
Joel

Another circuit - maybe a long distance opto-isolator? Fiber-optic type?

BOR - I personally don't think it's bad form to run without the BOR enabled, especially if that's what works for you.
But...I think I'd make sure you've got some extra error checking code in there to cover for you if you do get into a marginal power situation and your values are uncertain...some sort of recovery routine that gets executed once in awhile, maybe saves values in eeprom, then double checks current values against the eeprom, if any of them don't match, restore the whole bunch, use either onchip of offchip type eeprom. An idea I suppose...good or bad? I dunno...

[mister_e]

if disabling the BOR solve the problem... i would monitor the whole hardware first to know WHY. Once you know why, this also solve any other potential problem.

Any extra I/O? use it to do a Hardware Reset once in a while

EDIT: any real schematic, pcboard and installation picture would be nice.

[Pic_User]

Hi Joel,

If the PIC is really reacting to a brownout, either the Vdd (+) is dropping too low in voltage (compared to Vss) or Vss (-) is rising too high in voltage (compared to Vdd.

The PIC sees the voltage across it’s supply pins at a level below what the PIC16F88 considers to be a brownout condition.

The capacitors that we always suggest to bridge these pins, are intended to hold the voltage on the pins even if the rest of the circuit dips. That’s why the capacitors should be very close to the chip.

The large capacitor is like a battery that holds it’s charge, even if the charge sags for a short time.

The lower value capacitor is to trap any fast moving “transients” that whip through the circuit, snapping the voltage at a rate so fast, that the large capacitor’s inductance makes it too slow to react. The small capacitor should be a fast acting low inductance, low ESR type. Not just any old type.

There are measures that can help problem circuits.

If we visualize that the slow dip in the circuit voltage also discharges the larger value capacitor, along with pulling the PIC voltage. It would make sense to guard against this discharge. See Filter 1 The resistor allows the capacitor to slowly drain while the voltage sags. However, if the resistor is too large in value the PIC may not like the power up sequence. The resist affects both directions.

There are other ways to increase the effectiveness of the filters. Filter 2 has an inductor. Inductors slow high speed changes in voltage.
Filter 3 has a little of each.

Filter 4
Diodes allow the voltage to charge the capacitor and prevent the circuit from pulling it back down during the slow glitch.
<img SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1630&d=1179204818">
These are really just some of the common ways to prevent voltage at the pins of a integrated circuit from being affected by power sags and transient glitches that bother all types of sensitive circuits.
Look for decoupling, bypass and blocking with Google.
See: http://www.designers-guide.org/Design/bypassing.pdf
There are a lot of other circuit problems that can plague a beginner. Mister_e is correct, please show us, some of the technical side, of your setup.