Analog Gauges / Air-core meter

[James Paul]

 Jeff,

 I know a little about these 'air-core' meters.  I believe all of them have a
 turning range of 360 degrees, but due to pins on the instrument cluster panel,
 the ranges are limited to 1, 2, 3, or 4 quad movements.  Following are some
 examples.  Some are 90 degree range (Fuel guage, Temp guage, etc.), some are
 180 degree (Temp Guage, Oil Pressure Guage, etc), some are 270 degree 
 (Tachometer, and some temp guages), and some are 360 degree (some Speedometers,
 etc).  And yes, there are two coils in these guages and when fed in
Quadrature,  (phased correctly), they turn.   As far as drivers are
concerned, I'm at a 
 loss here.    I believe there are driver chips that are available to perform
 this function.  You possibly could use PWM from a micro to perform this
function also.  Regarding possible suppliers, I don't know of any so your
best  bet there is probably a junk yard as you indicated.   I know this
isn't exactly  what you  asked for, but I hope it helps you out nonetheless.






At 03:56 PM 5/27/98 -0400, you 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 would like to drive several analog gauges from a microprocessor.  I
>would prefer to use the new style gauges, if possible.  The only source of
>information I have found so far is National Semiconductor's LM1819
>Air-core meter driver datasheet.  Are there any other similar drivers
>available?  Would it be hard to design a home-built driver?
>
>My main question is where to buy these sort of gauges.  Is there a cheap
>source of new gauges, or is my best bet to scavange them from a junk yard?
>If so, are all air-core meters alike?  What differences might I find?
>Please note that I do not want to buy a whole tachometer (expensive) from
>someone like Autometer or VDO - I just want the gauge itself since I will
>be driving it from a microprocessor.
>
>I apologize for the length of this post, but I wanted to be as clear as
>possible.  I would appreciate feedback from anyone who has experience with
>this type of analog meter.  Thanks for your help - this list is a great
>source of information.
>
>Jeff Webb
>mustang at eel.ufl.edu
>
>
>