Re: toasting an O2 sensor, hesitation at boost, and more

[Orin Eman <orin@wolfenet.com>]

> It's perfectly -accurate- since it is derived directly from the 
> pressure sensor the ECU uses.  However, the -precision- is very low 
> and there is a slow refres rate, plus it is unknown whether the 
> ECU/board computer rounds or truncates the measured boost value.

The display is slow because the display in the instrument panel is
slow.  The signal that goes to the instrument panel isn't slowed down.

> >  A real VDO gauge is a good upgrade...HTH

> That's very true, and something I've considered for a long time. 
> Unable to find a good location though.  I thought about the cigarette 
> lighter socket, but couldn't figure out if the gauge would fit. 
> Certainly already has wiring for the lighting in the gauge.

I've been working with Pete Kunzler on an two digit LED boost guage.

If you have seen my duty cycle meter, the boost meter is based on
the same board.  The display is currently about 3/4" square by
1 1/2" deep.  We are working on a case so it can be mounted under the
top of the instrument panel cowl.  It fits here easily without
blocking any existing guage.  Currently, it has been tested reading
bar, like the existing guage.  It is wired into the same signal
and reacts so much faster that the digits can merge together as
they rise... I'll be slowing it down to make it more readable.
Other options are reading absolute pressure in inches Hg
or boost in PSI/vacuum to be decided.

A PSI/vacuum display would need a '-' added which would make the
display wider than it is now (and would preclude mounting it
in a switch blank).

Personally, I'll probably scale one to inches Hg - 0 to 60 gives
more resolution than 0 to 2.0 - 1/60th of full scale rather
than 1/20th of full scale.  For cars with no boost signal
from the ECU (A4 1.8Ts for example), we are looking into
pressure transducers, but unfortunately, the Motorola sensor
that makes most sense seems to be unobtanium at the moment.

Scaling can be done for any pressure sensor, assuming the signal
is 0 to 5V.

I'm working on dimming it for night.
We have the options of wiring it to the dash dimmer
(not so good if you turn the lights on during the day), a separate
dimmer control or using a photocell to control brightness.

There is a picture of one of the duty cycle meter boards/displays on:

http://www.wolfenet.com/~orin/electronics.html

Comments?

Orin.