Analog Gauges / Air-core meter

[Andrew Ghali]

On Wed, 27 May 1998 15:56:37 -0400 (EDT), Jeff Webb <mustang at cen.ufl.edu> wrote:
>
>I have a couple of questions involving analog gauges.  From what I
>understand, there are two main types of analog automotive gauges: the
>standard galvanometer-type meters, and the new air-core (moving-magnet)
>meters.  Is my terminology correct?  I assume the air-core meter gauges
>are the ones found in most new cars (where the needle does not return to
>zero when the power is turned off).  The air-core meters seem to use two
>coils (sine and cosine) instead of one coil and a spring as in the
>galvanometer type.

I think the single-coil design is called D'Arsenal (I'm sure I got that
wrong).  It's funny that you bring this up because I have been thinking
the EXACT same thing.  I wouldn't recommend movements out of dashboards
because they have no protection - no can, no crystal, nuthin (I have a
console  out of a '93 Rx7 in front of me and I'm trying to figure out
what to do with it).  If you get the application notes for the LM1819
(from the National Semi web site) they reccomend a movement from Faria
Precision Instruments, the MT-203.  Faria has a minimally useful web site
(use this as an example of how NOT to set up a corporate web site) at:
http://www.faria-instrumenst.com.
A better choice than the LM1819 for a ucontroller-based instruments is
the Phillips SA5775 Air Core Meter Driver.  This little beauty has a
serial digital interface and two 10-bit DACs that use a piece-wise linear
approximation to the quadrature drive required for the meter.  This page
lists the data sheets, application notes, and an application including
source-code with an 8051: 
http://cosmo.tky.hut.fi/~kosonen/prod/philips/philips.html

I'm still waiting on information from Faria, and I haven't tried getting
the SA5775 yet.

<editorial mode on>
I can't see why AutoMeter, Stewart-Warner, VDO, etc. are still trying to
sell crappy 90 degree D'Arsenal meters when it's just not that tough to
make REALLY good 270 - 305 sweep gauges.  It seems that the Japanese tuners
like HKS, Blitz, and Greddy are the only ones producing full sweep gauges,
so they charge $200-$300 each!  In AutoMeter's defense, they have introduced
one 270 sweep meter but it is a low temp coolant gauge - it only goes to
210F, which is nearly worthless for anything but maybe quarter mile trailer
queens.
<editorial mode off>

I hope this helps.

Andrew