measure gas flow microcontroller
You need an analog to digital converter, usually abbreviated ADC. Take a read of :
**broken link removed**
This will give a basic overview. You have several options, you can add an external ADC chip to your system. Or you can change your microcontroller to one that already includes an ADC function internally. Many larger microcontrollers have this function already. You just need to feed the analog voltage to the ADC input pin of the microcontroller and then write the code to read the internal analog to digital value.