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