Megasquirt A/D Vdd

[Bruce Bowling]

Hello Stewart,

Good question! It turns out that this micro (as many others) bring the Vref 
out to a pin for one to hook up the power supply. The Vref is the upper 
voltage range of the ADC. If you power all of the sensors off of the same 
power supply as the Vref line, the setup will be "ratiometric", meaning 
that if the Vref changes, all of the biasing for the sensors also change 
along with it, hence you will acquire the same count value (within ADC 
precision). This is a common analog power supply biasing scheme which 
preserves the accuracy of acquisition for varying reference levels, and is 
the way OEMs bias their sensors.

- Bruce


>Date: Wed, 21 Nov 2001 19:20:46 -0800
>From: Stewart Prince <sprince at csun.edu>
>Subject: Megasquirt A/D Vdd
>
>Just wondering about the megasquirt reference voltage for the  sensors and the
>a/d converter.  I Believe the lm29x7 has a +/-5% tolerance which would be 
>about
>+/-.25 volts in terms of the absolute maximum ratings.  Is that accurate 
>enough
>for the a/d converter & sensors?  Isn't a precision voltage reference with 
>about
>a +/-1% usually used?
>S. Prince
>
>- ----- End of forwarded message from owner-diy_efi at diy-efi.org -----

- Bruce



---------------------------------------------
              Bruce A. Bowling
          bbowling at earthlink.net
    http://home.earthlink.net/~bbowling
---------------------------------------------

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