I am new in this forum. I searched deeply in it but did not find similar project like mine. I will highly appreaciate your advise on following matter:
I would like to measure the oxygen content in percentage in exhaust gases of my pellet boiled by using simple and cheap LSM-11 narowband Bosch lamda sensor. Then to show it on display. Further development is to includ PID algoritm and control the burner fan speed (air quantity) in order to keep the oxygen content in flue gas constant. This will optimize the burning process and increase efficency.
I know, there are ready devices using wideband lambda sensor that give linear output 0-5v for oxygen 0-21%. But they cost about 200 EUR. However I am looking for cheap solution. LSM-11 is intended for O2 control in boilers. It has simple heating circuit and voltage output in range of about 1v.
The curve is extended in the lean side. This is the part that boilers use for lambda control. Not like in petrol engines the pellet boilers neads about 5.3% O2 in the flue gas for optimal fuel burning. I want to use only the lean side of curve -10 mV to 40 mV :
The output voltage commes from the 2 wires of the sensor and vary from -10mV to 40mV in the range in which I would like to measure the oxygen content in %. So it need amplification and shifting so the all analog signal is positive in order to be readed by Arduino analog input. I purchased one LM358 ready board with 2 stage voltage amplifier to play with it. I still wait for it to arrive. It is just a base on which I can chage the diagran as I want.
May you suggest a proper diagram for amplifiacion of this signal for importing in Arduino uno by analog input with resonable resolution - 0.1 mV should be enaugh? Should it be differential amlifier? How to shift the negative voltage so all output to be pozitive? How to limit the amplifier input only to 40 mV??? Or to limit the output insread? I do not need to read teh part from 40mV to 1 volt input. The curve is non linear but that I will corrected by program ways. So , even if amplification is not enaugh linear I can correct it in the program at the calibration stage. I suppose the input impedance should be enaugh high to not influence the output of the sensor.
Best regards, Gendov