panel meter needs independant supply ...

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hi, i`ve  finished building a power supply with , fixed 5,9,12,15 volts and
adj 1.3 to 26 volts .
i bought a led panel meter and when i connected it up to the  adjustable
side ( i powered the meter from the fixed  9 volts) it came up with a 1 in
the display, anyways if i powered it from a 9 volt battery the panel meter
worked perfect. looks like it needs a  independant  9 volts supply.

 is there any way around  this  , by using the power supply i already have
to power the meter , instead of a battery  ?

thanks,
mark k



Re: panel meter needs independant supply ...
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Yes, many of those panel meters do not like being ground referenced on
the supply side. Some have a link or can be easily moded for a common
supply, but others can't.
You didn't supply any details on the meter, nor your power supply
configuration, so it's kinda hard to help...
If you have a spare isolated tap on your transformer you can use that.

There has been talk about this recently on the group, search the
archives.

Dave.

Re: panel meter needs independant supply ...

What David said is correct.  I went through that experience a couple of years
back.  Ever since I have been asking specifically if the meter can be used with
a common negative, and they all eventually admit shyly that the answer is NO.

Luke Tubnor at Jaycar's tech support went through this with me at some length,
having already been there in his own experimentation.  You can sort of fudge it
if you are only using it as a voltmeter, but if you want to switch it between
voltage and current then that fudge isn't a goer.

If you havent got an isolated uncommitted secondary, the easiest ways -
seriously - are either to get a small transformer and connect that to provide
the separate (microamp) supply, or build a small isolated DC-DC switcher off
your bridge oputput.

It's a real bummer.

Re: panel meter needs independant supply ...
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Many years ago I built a simple inverter type circuit for a LCD display
power supply. It used a nand logic chip and a few other components. Have
a look around.

Re: panel meter needs independant supply ...

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Been there, done that, use a SRS-1209  miniature DC-DC converter module.

Google for it.

JD



Re: panel meter needs independant supply ...

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Some panel meters do not have that limitation:
http://www.mpja.com/prodinfo.asp?number16%565+ME
http://www.mpja.com/prodinfo.asp?number12%306+ME
For instance.

Re: panel meter needs independant supply ...

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which is a LED type.  They don't have any problem sharing a neg rail.  In fact
it is almost a requirement on most common units.

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which is more interesting (although from USA).

Mind you, many of the cheaper ones claim to be able to do it, but can't deliver.
Having been thusly disappointed before, I wouldn't get overly excited until I
had seen it perform.

Re: panel meter needs independant supply ...

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I can't speak for every place that sells them, but many of the LED meters
at http://www.mpja.com/products.asp?dept52% do not. I don't believe it has
anything to do with whether they are LED or LCD, but rather the A/D
converter or input amps.

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This is what I used the last time I needed an isolated supply for a cheap little
LCD meter (a month ago)

http://www.discovercircuits.com/PDF-FILES/ISOLATED9VSUPPLY2.pdf

I have used in the past a 4011 quad NAND gate to do exactly the same thing.
Scroll right to the bottom of the page for "floating supply..."

http://www.techlib.com/electronics/regulators.html

These are good for a couple of mA and work fine with an LCD meter. Not sure how
much current an LED meter draws.

PH


Re: panel meter needs independant supply ...
hi,   mine is a led panel meter , and draws up to 60 ma , the schematic you
mentioned  only has a 1ma ?

mark k



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you'll need a bigger converter for that (scrounge an 0509 from an old thin
ethernet card? they're good for 222ma )

or use an op-amp to shift the input voltages:

http://www.jprelec.co.uk/docs/PImages/pdfcopies/375-102.PDF


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I was wrong - actually 56mA, same as the 1209 mentioned previously
4mA to few for you, (maybe enough if you leave "half a digit" dark)


Re: panel meter needs independant supply ...

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Yep, a milliamp or two which doesn't help you if your LED panel meter draws
fifty times that.

Other posters mentioned the possibility of a tiny mains transformer,perhaps
salvaged from some small mains powered junkbox device like a radio or even the
guts of a low current plugpack. Depends on how good your junkbox is.
That SRS-1209 DC-DC converter mentioned by another poster is available in
Australia from
http://www.computronics.com.au/meanwell/srs /
56mA out for $7.10 plus of course whatever they want to bite you for postage.
They look very handy in a DIP sized package. I may even get some myself to save
me reinventing the wheel next time around.

PH


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As a lateral thinking idea for your next project, use a $20 DMM from
jaycar etc instead of a panel meter. Make it visible via a cutout with
connections made internally, and provide a 9v supply from your main
supply. Will be cheaper and easier.

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Huh?  Same problem exactly that the O/P raised.

Re: panel meter needs independant supply ...
Hi Rebel,
        Jaycar have a small PCB kit which uses radio IF coils and and an
oscillator circuit creating an isolated supply to drive an LCD panel meter.

    cheers,
        Dex


rebel wrote:
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Re: panel meter needs independant supply ...
Hi Rebel,
        Oatley Electronics may have it also can't remember exactly, so many
websites so little time.

    cheers,
        Dex


Dex wrote:
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