Gas sensor help

matrixkid44

I was looking into gas sensors. http://www.parallax.com/catalog/sensors/gas and i see that there is a gas sensor board for the gas sensors. Is the board used to make it so that the outputs are digital? Because the gas sensors alone are analog? Also from the data sheet it shows that there are 4 pins on the board. One for ground,Power, ALR, HSW. The data sheet says input for detecting the alarm signal (ALR) and the other an output for controlling the internal heater (HSW). I am kinda confused on ALR and HSW. ALR is the alarm that triggers that something is wrong? HSW is the output to the microcontroller to tell you something is wrong? Also can you tell me what HSW mean. I tried to google ALR and HSW but i still don't get it.

Thanks for your time.

Chris Savage

Welcome to the forums! The gas sensors are analog and resistive in nature, however they only function when the heater is energized. The Gas Sensor Board provides an easy way to experiment with the sensors by providing a circuit to drive the heater and a buffer with voltage divider allowing you to set a trip point and see when that trip point has been exceeded. The documentation describes the details in more depth including the pins, but essentially HSW turns the heater on/off and ALR goes high when the gas level exceeds the preset point.