I can find lots of LCD & LED 3-1/2 panel meters for under US$20. But look for
4 digits and the price triples.
Is this just my experience, or is this pretty standard pricing?
I'm flexible re. type (prefer LCD), background lighting (not necessary),
color (prefer green), and size (have ~25mm x 50mm panel openings waiting to
I've looked at Mouser & Digikey. Spendy!
Where else to look?
I would say that the $20 meters you found were probably not "standard
pricing" but were probably no-names.
Very very few real-world applications can use the extra digits
usefully. There are some customers that really need it, but most
customers demanding more digits are on an ego-trip :-).
The demand for standalone meters seems to be getting smaller and
smaller as everyone moves to microcontrollers and commodity A/D that
actually matches the resolution/accuracy needed. If you need isolation
then you have to think a bit. In a lot of one-off applications it
doesn't pay to think, you just buy the standalone meter!
Want to replace the analog meters in my bench PS with digits. It goes beyond
20, so I'll need 4-digit meters, yes? I'd like more than 1 decimal place.
Maybe I've got it wrong... How do these meters work? Do they show the max
decimal places possible (
Typically the surplus 3.5 or 4.5 digit DPM unit itself is either 0-2V
full scale, or 0-200mV full scale.
Some units can be jumpered for either, and some other ranges
(including current ranges) are available. If you buy from a
distributor you will have much better choice of ranges compared to
buying a surplus unit.
You are responsible for adding the dividers/shunts if you want, and
you are responsible for putting the decimal point where you want.
If you want 0.1V resolution, then a 3.5 digit meter gets 0.1V through
199.9V. Or at 0.01V resolution, a 3.5 digit meter gets 0.01V through
19.99V. As commonly incorporated into low-end power supplies, you
might find a slide switch that changes the divider and the decimal
I would seriously question the need (other than "ego trip") of going
to a 4 digit meter. Especially if (for example) you aren't buying 0.1%
or better resistors for your divider or shunt already.
You also may have to look at where the power to the DPM module is
coming from if you do not have a separate isolated power source just
for the meter and you need to float the meter reference above ground.
One often-seen option is a battery.
"Tim Shoppa" wrote in
If you are powering from the same regulator that powers a sensitive circuit
that is outputting millvolts for measurement, take care, especially if
you're using an LED meter. The meter can change the load, the load
regulation might allow the other circuit's output to change, in turn
changing the meter reading...
The easiest way to avoid this really vicious cycle is to use separate
regulation for the meter and the measured, or even to isolate them with
separate transformer windings, if battery power is not important.
There may be other, better advise to come on this subject. I hope so, cos
I'll be watching it avidly if there is.
Why over work the human operator ? Use a
ARM STR710FZ2T6 mcu..
Thats what im doin .
I will hook my MFJ209 to it and create
a DMM . A super MultiMeter ...
Test Coax , read the true inductance
and capactance and Q .....read real stuff
as the circuit is actually working ...