O2 Sensor Voltage Detector

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 + 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

Reply to
BretCahill
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a 50

mileage

small LED

gas.

there

an

I did more or less this as part of the LPG control system on my Merc. I took the O2 (lambda) sensor and fed it directly (bigish resistor to limit current) into the AtoD of a 622 PIC and had about 7 LEDs on it, yellow in the middle, red = rich and green = lean. It worked fine with very few external components. There was one major problem in that the PIC wouldn't work off the voltage I needed (very close to supply minimum), it failed to boot correctly so I added a bit of code that switched a resistor in the voltage supply regulator to drop the supply voltage once the PIC had booted so that Vref was low enough for the lambda sensor with no amplification needed.

Reply to
Mjolinor

The O2 sensor also will be damaged if you draw more than a few microamps from it. Make sure that the load resistance is in the meghoms.

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Terry

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