Support for gaz sensor
The universal support for gaz sensor from Parallax is designed to work with the followind sensor:
- CO (Carbon Monoxide) Gas Sensor
- CH4 (Methane) Gas Sensor
- LPG (Propane) Gas Sensor
- C2H5OH (Alcohol) Gas Sensor
Just plug the sensor in the univeral support in order to measure the gaz concentration in the ambiant air help by your favorite microcontroler(For example the Arduino UNO SMD Board). It's realy easy to replace one gaz sensor by an other one, allow you to adapt this devie to your needs.
The universal gaz sensor support integrate an easy to use 4 pin interface :
HSW: heater, active on HIGH states. Some of sensors like the CO-sensor divide their functioning time in two part sensing phase and purge phase (each phase have different duration). For example, if you want the CO-sensor to enter in the purge phase, you must apply a voltage in range 3 to 5V on the HSW pin. Without such a voltage the CO-sensor will stay in sensing phase.
ALR : This pin is passing through low level to high level when ever ther gas sensor detect when a too high amount of gaz concentration is detect. It this pin that your microcontroler must read in order to detect the high level of gaz concentration.
It remain to you to chose the maximun gaz concentration tolarate by your system. Adjusting the V- voltage. As you can the in the above picture, the gaz sensor support integrate two potentiometer.Each of them is link to one of the two enter of comparator as shown in the below picture :
When the voltage apply at the V+ pin of the operational amplifier is higher than the V-, the amplifier output pass from low to high. Then you can detect a to high amount of gaz concentration.