O2 Sensor Voltage Indicator

[BretCahill]

I have an old carburetor aspirated engine with an O2 sensor. In the fuel
efficient mode, the O2 sensor dithers around 0.4 volts with the computer
opening and closing a solenoid valve every second or so. I can splice in a 50
K ohms/volt dc voltmeter and immediately see when I'm getting good gas mileage
but I don't like a voltmeter on my front seat and I want to install a small LED
indicator light instead. When the LED was flashing I'ld know I was saving gas.

An O2 sensor puts out too little current to power anything by itself. Is there
any way to wire up a 741 op amp and battery or other cheap circuit to power an
LED when the voltage goes above 0.4?

I'm guessing I'll need an amp gain of about 1000 and a voltage gain of 5.


Bret Cahill

 

[Baphomet]

An O2 sensor puts out too little current to power anything by itself. Is
there
any way to wire up a 741 op amp and battery or other cheap circuit to power
an
LED when the voltage goes above 0.4?

I'm guessing I'll need an amp gain of about 1000 and a voltage gain of 5.

Try a 339 or similar comparator
http://www.fairchildsemi.com/ds/LM/LM2901.pdf . An op amp would work but a
comparator will have a more stable "trip point" and will certainly have
faster rise and fall times, not that this should be of particular concern in
your particular application. The output transistor (Q8) has an open
collector so an L.E.D. (observe polarity) in series with with a 2.2K
resistor from Vcc to the output collector should do just what you need. You
can derive your reference voltage of 0.4 volts from a simple resistive
voltage divider from Vcc to gnd. if your supply is sufficiently regulated.
If not, you can use a zener diode network as you reference.