Jaycar QP5570 3.5 Digit Panel Meter

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Last week from Jaycar I purchased a QP5570 3.5 digit LCD panel meter.  I
cannot get it to operate in a common ground application.  I require it to be
a 200 mV voltmeter.  The instructions and box that it came in say it can be
used as a common ground meter but do not say how.
Can anyone please assist?

Regards
Glenn



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Re: Jaycar QP5570 3.5 Digit Panel Meter

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been there, done that (as in had_that_problem) and discussed it at length with
their technical person (Fred).  I have emails and a hand-drawn schematic of his
efforts to get a true common negative configuration to work.

Basically it can't be done.  Front up back at the store and get a refund.  If
they get diffcult about it, ask them to demonstrate how to achieve the described
result.

Re: Jaycar QP5570 3.5 Digit Panel Meter

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Not sure if they are the same meter, but I have bought a couple of the
Q2220  meters from DSE - these come with a diagram of how to achieve a
common ground application

I could scan the circuit if you want to have a look at it as it might
work for the jaycar unit

David

Re: Jaycar QP5570 3.5 Digit Panel Meter
On Thu, 13 Mar 2008 11:01:10 +1100, David

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If  ti shows a resistor network between the - and "ground" then it won't work as
a true common ground.  The Jaycar behind-the-scenes tech bloke confirmed it does
require a slight negative bias to be able to operate properly.  A true common
ground system would require ONLY a scaling resistor divider, with the - and
ground terminals directly connected.

Re: Jaycar QP5570 3.5 Digit Panel Meter

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The DSE circuit uses a pair of 7805s driven by a bridge rectifier

David

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