At 03:11 PM 3/10/97 -0500, Shawn Ellis wrote:
>Well, The schematic is in Autocad DWG and its kind of ad-hoc, so I hesitate
>to tarnish my rep by sending this nasty thing out...  but if you can deal
>with DWG or DXF I'll be glad to Email it to ya!  Yeah, that sensor problem
>was a different system which I plan to optically isolate, this system is
>interfaced to a device which holds the I/O line high via a separate power
>supply (in the PC)  and that always puts a few extra millivolts on my
>power-off.  Should I perhaps use a diode/relay/analog switch to turn off
>the I/O when power is off?  I hope the optical isolation helps with the
>other problem... mabye thats what I could do here as well.... But I DO need
>something extra, because even with everything unplugged, the system STILL
>holds enough voltage in the filter caps to screw it up even over-night!
>
>>
>> Can you send me a .GIF or Protel schematic which shows where this extra
>power
>> is coming from AND getting coupled back into the PIC ? Or how about an
>ASCII
>> representative schematic ?
>>
>> Rgds
>>
>> Mike
>> Perth, Western Australia
>>
>> There is no a'priori reason that the ultimate truth will be interesting
>> or even useful, those moments of frustration during philosophical debate
>> would be replaced by the sheer terror which accompanies true knowledge.
>
>
Did you try a diode from the VCC to the MCLR line? This way if the VCC drops
the chip is forced to reset. Normally you pull this line up thru a resistor
but putting a diode in parallel with the resistor will cause the loss of VCC
to pull the reset low much faster than it will go up.
Larry
Larry G. Nelson Sr.
L.Nelson@ieee.org
http://www.ultranet.com/~nr