[MRCA] [ARC5] Hamfest DVM modules

[mstangelo at comcast.net]

Jeep,

I believe the power supply ground is not referenced to the meter input ground. You have to power the meter with an isolated supply like a 9 volt battery or from a power transformer secondary.

Mike N2MS

----- Original Message -----
From: DSP3 <jeepp at comcast.net>
To: MRCA at mailman.qth.net, arc5 at mailman.qth.net
Sent: Sun, 08 May 2016 13:10:18 -0000 (UTC)
Subject: [ARC5] Hamfest DVM modules

For what its worth, I bought two of those small, pop-in 3-digit, panel 
mount voltmeters at the Hagerstown fest, yesterday.  No documentation, 
whatever, is provided.  The idea was to add them to a couple of LV power 
supplies I have that are meterless.  Well, they don't work very well, at 
all, I believe. They are powered by about 3-9v DC.  The ones on display 
appeared to be just fine.  I wired both of them up to batteries and 
power supplies and, with proper Vcc applied, got readings typically 
20-30% high along with a 2v-4v instability.  I thought that perhaps the 
meters were responding to noise and/or ripple but the 9v batteries 
connected exhibited the same error and instability. The meters do appear 
stable with only Vcc applied and indicate 00.0v.   Anyone have any 
experience with these little DVMs?  Is additional filtering required?  
Are they maybe AC meters with a high crest factor and a bridge on the 
input?  I have no idea.......

Jeep - K3HVG