MQ-7 CO Module Setup

17 has the answer.. The heater is series with 82 ohm to give 1v4 to heater. A mosfet is used to bypass the resistor..

I'm unsure if PWM (30% on) is OK for the low votage .

17 If I want the output of CO data in ppm( i.e. 100ppm in place of 235). what formula has to be used in this code?