I'm using 2 PP3 batterys to get +9V and -9V for op-amps used in the
continuity circuits.

Problem is the circuits detect continunity by creating a short with the
ground of the circuit.

If probe A is connected across a door sensor to check for continuity then
just connecting the non-grounded probe of B will

cause if to think there is continuity.

I could use seperate batterys for each probe but I will need to have a lot
of these circuits to check for continuity in
different parts of the same loop.

The loop is a series of door sensors about 20 sensors in all which when all
doors are closed just creates a short between 2 points. I want to use this
circuit to display, using LED's at each door,2 sensors per door, that the
door is closed properly.

                        ProbeA  ProbeB

                        ^     ^     ^   ^
                        |       |       |       |
                        |       |       |       |
                        |       |_____| |
                 Op-Amp    |            Op-Amp
                                  ---
                                   -
                                Ground
-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Chris Carr
Sent: Sunday, July 29, 2001 3:49 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Isolating ground


Two batteries, one for each section.

or Switched Mode Power Supply with isolated secondary windings

or if you have circuitry common to both inputs, either

use linearised opto-isolators or
chop the input signals at high frequency and transfer to the common
circuitry using transformers

No.... the answer cannot be that simple either I am missing something or you
haven't stated the complete scenario

Regards

Chris Carr

> I'm using a circuit that has 2 section powered from a battery. Is it
> possible to isolate the ground signal from both sections so that there is
no
> connection between the grounds from each parts for the circuit.
>
> The circuits are 2 continuity circuits which detect continuity throught
the
> ground of the circuit but I wish to use both circuits in different
sections
> of the same loop but the ground from circuit 1 probe will affect the
> dectection of continuity by the section 2 probe. Is there anyway around
this
>

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