Ed Anderson used the same chip and expanded the dynamic range with this
skematic.

Rob Weinstock wrote:

LM3914's can be chained to provide any degree of resolution you like.

IMHO,

it's a bit of a waste of time, since the EGO sensor only provides a
meaningful measurement of "lean" or "rich", with a healthy hysteresis in
between. Any values reported by the display between these extremes are
inferred by the circuit from simple averaging techniques -- it's just
charging a capacitor.

To do this properly, you need a wide-band O2 sensor. Honda uses these on
their latest cars, and they are expensive to the DIY'er. There is

another

list on the 'net for DIY EFI folks. They posted about this topic
exhaustively perhaps 6 months ago.

>From an engine tuning perspective, you would probably want to use a

real gas

analyzer anyway. And this circuit is useful for detecting when the

mixture

is simply lean, which you would want to know in order to avert problems.

Regards,

Rob

Ed Anderson wrote:

I agree Rob, that the area between "Rich" and "Lean" is not very informative
for our needs.  My design spreads 10 LED "bins"  in each the "Rich" and
"Lean" areas and only has one LED that responds in the "Dead" (hysteresis)
zone between the two zones of which I am not interested.  With the  O2
sensor curve available you can sort of calibrate the Rich and Lean zones and
have a fairly good idea of where on the AF curve you are operating.  Having
tried tuning without one and with one, I find that it quickly gives you and
indication of where and which way any tuning adjustments are headed.  For
instance, I notice that if I turn the mixture down too lean, the LEDS
indicates this before the engine starts to stumble and I can hastily adjust
the mixture before giving myself a heart attack {:>).

Of course the Wide-band O2 sensor and other high resolution meters would
give a more accurate reading, but as you point out they are rather
expensive.  For $20 worth of parts plus the cost of the sensor, I think its
a useful instrument for the price.
FWIW

Best Regards

Ed Anderson

The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org