Rob,
The National LM3914 (or equivalent) looks like a good start, as it will work
directly from 12v and directly drive up to 10 discrete LEDs (or an LED bar
graph). I've attached a circuit for a cheapo O2 meter (basically a bar
graph using a 0-1.25v input).
For your 0-15v circuit, you would probably want to use a precision divider
on the input, say 2:1 to get 0-7.5v; and then put a divider on the LM3914's
voltage reference to bring it up to 7.5v. The complete data sheet at
http://www.national.com/ds/LM/LM3914.pdf
Shows how to adjust the reference voltage (page 8). There are also some
good notes in there about how to keep the LED current from messing up your
measurement (due to voltage drop on the ground side).
A quick Google shows the LM3914 available for as little as $1.50
http://tinyurl.com/yd9bwtj
Lots of LED displays available, of course. Here's one at Digi-Key that
looks suitable, for $1.05.
http://tinyurl.com/y8ucvww
All this assumes you want to "roll yer own"; no doubt there are commercial
solutions available as well.
-- Randall
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