Hi, i want to measure the CO and NH3 concentration and when it reaches to warning value then the PIC turn on the alarm and other things, with this application i think i can use MQ7 and MQ137 sensors, i attach you the application circuit of MQ series.
you can see MQ7 and MQ datasheets in this page:
http://www.hwsensor.com/English/prod...iconductor.htm
i think i should use MQ7 and MQ137 with this application, so i think i should use MQ series application circuit( that i attach you) and i can adjust the warning value with putting a potentiometer instead of red circled resistor in the picture(attached file) and turn it until adjust to warning value . am i right?
but how can i calibrate the sensors in clean air? how can i understand that the value of potentiometer reaches to the suitable value ?
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