Jaycar QP5570 3.5 Digit Panel Meter

[Glenn]

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

 

[David]

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.

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

 

[David]

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.

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

David