On Thu, 21 Sep 2017 17:21:23 -0700, mike wrote:

snip read and well meaning stuff for brevity

Words like exactly, "as good as possible" have no place in a specification.

I guess that depends on your background, viewpoint and goals mike?

e.g. I knew what I wanted, had a rough idea how it could be done and
just thought I run it past the panel for some real world *design*
feedback (I'm very much a dabbling designer but long term builder /
support guy etc).

Specs are numbers and test methods. Specs include allowable
variations due to initial component tolerances, component age,
temperature, vibration, misuse.

Understood. I felt I laid out the relevant spec on my initial post, or
at least as far as someone who understood humans were concerned. ;-)

"Not a 'repair' question as such but I was thinking of using an old
skool 250uA FSD moving coil panel meter to read the 10 to 15V DC range
(a lead acid battery charge / discharge indicator), next to a 0-30A
Ammeter (inc shunt etc).

I was thinking of using either a voltage reference such as
LM4040DIZ-10.0 or could I get away with a simple zener (BZX55C?) with
associated resistor(s) please?"

So that was the need, the specs as far as I knew them and a potential
solution to help people 'get' what I was considering. What I didn't do
was signpost the fact that I was actually using a 0-5V panel meter to
display the 10-15V range. ;-(

The 'human' bit: A small (key fact) analogue (key fact) panel meter
connected to a lead acid battery (key fact) needs reading and those
readings interpreting and so ITRW, we are 'most likely' to not require
much in the way of precision or we wouldn't be using those things in
the first place. ;-)

So, what I was hoping I was saying is 'Could someone confirm or
recommend that 'for the (reading_between_the_lines) reasonably 'soft'
requirements, what is likely to offer *a* (there may be many equally
competent) real word / human solution?

So, anyone who knows their stuff and who understands people *might*
have already answered the question on 'how much money', 'how much
effort', 'how complex / simple' would any solution likely to be in
their heads. shrug

An example of misuse is, "what happens when the user hooks it
up backwards."

Understood, but unbeknown to anyone here, that will all be catered for
*in my case* by the use of polarised connectors that could never end
up reverse connected elsewhere.

I learned about vibration when I carried a
voltmeter on my motorcycle. When I needed it, it failed.
I took it apart and it poured out like sand.

Again, understood. In this instance the only clue I gave to the
potential size of the battery was the scale of the ammeter (0-30A) and
that scale was because it is to be used on an electric outboard motor
that has a maximum current of 30A and will in fact be running from 3 x
31Ah batteries joined in parallel. Because it's in a boat the panel
meters will have a very comfortable ride. ;-)

The engineer doesn't need to know WHY you want what you want.

Quite. ;-)

That's not his job. HOWEVER...if you state your objectives,
why you want to do this, you might find the bevy of rocket scientists
have a much better way to accomplish your objectives.

Again, how would knowing what I wanted to use it for, more than I
already specified help anyone actually resolve the question asked? I'm
not saying they couldn't then rule out or add 'other things' but
nothing offered so far has affected the physical outcome of this
particular project in a physical sense.

That said, I could have been using a large and expensive panel meter,
graduated in .2v increments, rather than one only marked in whole volt
increments g. But the reading of the meter is my problem, making it
read 10-15V is the bit I needed help on (please). ;-)

As an aside here ... I ran a Telephone Help Desk for over 5 years and
feel I became fairly good at 'gauging' people. If their opening gambit
was 'Your beige box isn't working' I knew to deal with them at a
different level (initially at least) compared with someone who said
'Our X.25 PAD No3 doesn't seem to be bringing up a Link LED?'.

Just the same as the PC user reporting that their 'screen is blank'
when it in fact has a flashing cursor in the top left corner. It's not
what they expected or wanted but it's far from 'blank'. ;-)

I can't
count the number of times a user wanted an complicated gizmo,
but his objective could be achieved with a much different
and much simpler approach by repartitioning the system.

Oh, absolutely and you / anyone (who hasn't already dealt with me on
here) wouldn't have any idea what I do or do not know and may have
already considered. My solution potentially required 2 components
(resistor and zener) so it couldn't get much simpler so it's just a
matter of selecting the 'best' (all things considered) types of those
components, if they are appropriate.

End rant.

Points noted and generally agreed mike. ;-)

First question I'd ask is, "are you gonna' stare at the meter 24/7?"

No, it's something I'll glance at either now and again or specifically
when I change something and need to see the consequences (like
changing 'speed' on my electric outboard.

If not, get a cheap digital panel meter off EBAY,

Already Done.

put a push button
in series and be done with it.

No need mike. It will likely only be in circuit when required
(testing) and the current drawn when it is will be insignificant
relative to the other loads and battery capacity (93Ah).

If you're not battery
powered, you can probably tolerate the load and don't need the
push button.

Check.

But, back to your original request.

Cool. ;-)

Take your current meter.

Check.

Put a series resistor to set the max voltage to 5V.

Check (~20k?)

Put a 10V "battery" in series.

Bench PSU + DMM, check.

The remaining question is, "how do you implement the 10V
battery?"

Check.

Can your measured voltage ever get below 10V?

Hopefully not. It will only ever be 10.5V or higher or 14.4V or lower
.... or disconnected completely (points already considered etc).

If so, your problem just got a LOT more complicated.
See "misuse" above.

Quite. ;-)

If it were me, I'd use a 10V zener diode. If you can find
an affordable temperature compensated one that is accurate
over the range of current from zero to the max indication
on your meter and the ambient temperature range, do that.

Check. I did suggested a BZX55C in my OP but not being a designer I
would have no real idea where to start re finding the 'right'
component (by that I mean there is probably a 'go-to' device that
'most people' would typically use under these circumstances, like they
might a 7805 or 555) ;-)

Characterize the calibration.

Ok?

Fire up your CAD program and make a new meter face.

Unlikely (see all the above). ;-)

Since you're making a new face, any stable zener voltage works.

Chances are I'm not so ...

Your meter is as accurate as your care in making the new face.

Quite ... and with simple 1V increments over a 10-15V range should
give me a better 'feel' of the voltage than trying to read a similarly
sized meter graduated in .2v increments in the 0-15V range all whilst
going along a river in a small folding boat. ;-)

Are we having fun yet?

Very much so, thanks mike. ;-)

Cheers, T i m