This circuit uses one LM324 is a Quad Amplifier. this circuit uses 2 amps per O2 sensor, so it will work to adjust two O2 sensors. As in the photo above, the top half of the circuit board controls the #1 O2 sensor and the bottom half controls the #2 O2 sensor.

Well, you need the parts shown on the schematic, soldering iron, solder, wires, multi-meter, the usual stuff to build small electronic circuits. The multi meter can be attached with velcro to the dashboard for a temporary voltage monitor.

Yes you will need to CUT the O2 sensor wire, so the wire from the O2 sensor connects to the input of the circuit and the output of the circuit connects to the ECU or ECM

The circuit needs to be adjusted once it is installed under your dash board. Easy to do with a Multi meter.

Locate all the components :

Layout all the resistors first, gold sized bands to the center. The position of the resistors really does not matter, they un-polarized. Don't solder them in until you place the IC socket for U1 Start soldering in the resistors. Add the U1 Quad Op Amp IC chip in later, when the circuit has cooled. You will have to make short jumper (22-24 awg) wires from Pot 1a and 1b from underneath the board to the dual stereo pots. VR1 and VR2. Bend the U4 • voltage regulator 3 pins back as in the photo. The right placement makes the pcb board fit perfect into the box, with 4 corner spacer standoffs on the bottom of the board. Remember to solder the C1 - Capacitor (blue barrel) correctly, the banded side with the shorter wire, is negative and goes into the round hole, the square hole is positive on the Cap. The Cap in the photo below was soldered on wrong, it was later fixed. ( Right when you always thought all square holes meant negative.) That threw me the first time. Always follow the schematic when it comes to components with polarity. Such as the LED lights (D1 & D2 ) they have the shorter cathode wire go into the square hole, The flat side of the LED light on the screen print on top of the pcb board lines up with the tiny notch on the plastic cap of the LED light. The notch is the negative cathode side. Also the Voltage Regulator has to be on right, the photo below is correct.

Below shows you how to hook up one of the IK pots in stereo or dual mode for 2 sensors with the same signal control.

How to Adjust the Dual O2 Sensor Control circuit.
(from CLadio Cabete the designer of the circuit)

It is very important that you follow the following steps to adjust the circuit so it will not trigger your check engine light.

Once you have the circuit all soldered up and ready to install :

Apply one VOLT to the O2 sensor input "J1" ( Your O2 sensor signal wire puts out millivolts under one volt and you can do this adjustment as you install it.

Use a Voltage Supply like a "variac.com" type bench voltage generator, to acheve a 1 volt to test the circuit board. Your car's oxy sensor (+) will vary up to one volt. 250mv = lean, 800mv = rich (approx.)

Soon we will have instructions on how to take a 1.5" AA battery to do a bench test of applying one volt. If you have the correct size resistor, (approx. 5M resistor) you can get a 1.5 volt battery down to 1 volt, by attaching the resistor to one end of the battery. Then do the adjustment test as written above.

Adjust Pot 1b so you have MAX voltage on Output to ECM "J3" Also the LED should light up bright.

Adjust VR3 so you have no more than one volt at J3.

That is it for this side of the circuit. Now perform the same steps for J2 and J4 and Pot 1a.

Note: Pot 1a and Pot 1b is the Mixture adjustment and should be selected according your car needs:

If you want to control 2 pre-cat sensors then you should use a dual Potentiometer just like the ones used for Stereo volume control. This way it adjusted both sensors at the same time.

If you want to control one pre-cat and one post cat, then 2 1k Potentiometers should be used for Pot 1a and Pot 1b. This way you can adjust the signals separately.

If you want to control 2 pre-cats and 2 post cats, then you need 2 circuit build using the Dual Potentiometer in each circuit.

This is the instructions for now, more will be added later. ( 9/9/08)

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A good question and answer from customer :

Hello Electrojolt

I'd like to get more adjustment range from "0" offset to about 400 mv. In the meantime, the first pot was adjusted for a 250mv offset at minimum, which gives a reduced 150mv range from 250mv to 400mv maximum adjusting the output pot. To return to normal (no offset) I switch the unit off. What changes in resister values can be made to increase the range. Also, the brilliance of the LED varies at different settings, have you redesigned the output circuit so the LED is consistent?

Thanks for your help.

Mr. x

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Hello Mr. X,

Ok, the circuit operates as an amplifier, so it will boost the original O2 sensor signal.

When you have the Gain Pot adjust to Max. lean, it should send a 0.7 volts to the ECU when the O2 Sensor as about 0.2 to 0.3 volts. You should not have to change this. increasing the gain will cause the check engine light to go on.

Now about the LED.

The Led is not supposed to be constanly Lit. It should blink, every time the LED light up, it means it is telling the ECU to Lean the Mixture.

The LED is also used to regulate the output voltage to prevent it from going over one volt. If you go over one Volt it will also trigger your check engine light.

that is the purpose for that last Pot, once Calibraded, you should not mess with it.

Electrojolt

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