Thanks for the reply. But I don't think that will help in this
situation. It is not simply an issue of getting appropriate voltage to
the display. There are 4 pins on the display. Two are the +/- that
are rated from 8-12 volts dc to power the display. The other two pins
are the hi/low inputs (200 mA meter). I tried to isolate the circuits
by supplying the display directly from the 12 volt buss and then
powering the quad op amp off of a lm7805. Both circuits run fine until
I hook up the LOW input to the ground on the amplifier circuit. Then
the display goes into error mode. I don't even have to hook in the
HIGH sense line and it goes to error mode. What seems to happen is
that both the negative (ground) pin of the dc power and the LOW sense
line pin are essentially grounded together and it simply won't work
that way. I'm not electronically sharp enough to think of any way of
isolating the two circuits without a battery.
Roger


On Feb 28, 10:45 am, "comanche driver" spamawayassh.ole wrote:
use a lm7809 voltage reg on a heat sink from the 12v in to dirve the
display.

"dodger" wrote in message

oups.com...



I'm attempting to build the RST Digital Engine Monitor (Kitplanes Feb.
2002). I could not find the LCD panel meter specified in the plans or
even the substitute mentioned in the addendum (http://www.rst-engr.com/
kitplanes/KP0202/KP0202.htm) so I tried to substitute one I found at
All Electronics (PM_200). I can get the circuit to work ok except I
need to power the panel meter with a separate 9 v. battery. Whenever I
try and hook it into the common dc circuit it goes into error mode.
Apparently, it needs an isolated power supply. Do you have any idea if
there is a way around this? It would be such a pain to have to
periodically change batteries behind the dash, not to mention it would
undoubtedly go out at the most in opportune moment.

Thanks,
Roger- Hide quoted text -

- Show quoted text -