Re: Boost Guage Accuracy

["Douglas Hurst Quebbeman" <dougq@iglou.com>]

..snip..

> >And the ECU samples
> > this and then writes some value to the boost guage.
> 
> No, actually it is much simpler than that, the analog signal from the
> pressure transducer gets split and sent off to the boost gauge. An op
> amp is used to buffer the signal. If you remove the ckt. boards from the
> metal frame, you can easily trace out the circuitry because only two
> layer boards are used. The gain of the op amp can be changed to rescale
> the boost gauge readout. This is normally done in the case when you
> change out the stock pressure transducer with the 2.5 bar Motorola
> MPX4250 unit. IC2 on the analog board is the quad op amp used for this.

Damn! Another fine idea shot to hell by another gutless wonder
designer!

Ok, I'm really in a dark area w/r/t my skills in the analog 
department. When you say "split off", in the digital world, we
worry about fan-out; a TTL gate can drive typically 10 inputs.
But I have no idea what the equivalent is in the analog world.
Is the op-amp buffer used specifically for this purpose?

> There is a uP/controller in the dash assembly (dash computer) that is
> used to convert and display this analog boost signal on the LCD. The
> response of this display is VERY slow. You can change the analog voltage
> input to the display and it takes several seconds before it changes to
> the correct value. This would make for a good project for someone, to
> sort out why it responds so slowly. 

Crap.

If anyone has one has an extra on-board computer they wouldn't mind
me trashing, I'd be willing to spend some time investigating this.

> > Does anyone know of an ideal pressure transducer for this
> > application? If not, I guess I'll have to dig out the latest DigKey
> > catalog and get to work...
> 
> Motorola MPX4250 0-250kPa, absolute, designed specifically for turbo
> charged vehicles.$20-35 depending on quantities and package style
> selected.

Couldn't find this in the Digikey catalog, but the one I checked was
almost 2 years old. All it listed were some stainless steel pressure
transducers from MPS. 

I'll look for a newer catalog, I know I have several...

thanks for the comments and info, Scott!

-dq
 
--
-Douglas Hurst Quebbeman (dougq@iglou.com)            [Call me "Doug"]
    QuattroClub USA# 4536              Audi International # 100024
       74 100LS Auto, 77 100LS Auto, 84 Coupe GT, 86 5Kcstq   
"The large print giveth, and the small print taketh away."  -Tom Waits