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Re: Boost Guage Accuracy


> >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

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. 


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!

-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