If this can help, the sensor has a heating resistor 33R and a sensor which is very sensible to low temperatures, but less to higher temps. So this means that to use it, you should make the following connections :
- one "H" to 5V
- the other "H" to a NPN transistor (collector)
- the transistor's emittor to ground
- the transistor's base to a 10k resistor
- the other resistor wire to an OUT pin of your micro
- one "A" to ground
- one "B" to a 47k potentiometer AND to an ANalog input
- the other two pot wires to ground
I believe that you can replace this pot by one 22k resistor since you'll use an analog input.
The working is a bit weird : this detector consumes nearly 1W continuously, and apparently needs to be heated 24hours before stability ! I'm surprised this would not bring the beast above the 50°C where the diagram ends, so I suggest you check the temp wit your (wet ;-) finger, but that's another story.
Power your system, set the heater ON, record the voltage (ANalog input pin) every 30 min, it should go up and then stabilize.
When there is no gas present, or say, less than 10ppm, the Rs is higher, so your analog input should be around 1.5-2V. When there is gas, the resistor goes down, so your analog input voltage increases (expect 10-20%). You should select a threshold above the first measurements, with some safety margin against false alarms, then test with real gas. Apparently you can use alcohol to test, but if the sensor is hot, be careful not to put fire to it !
There is no "formula" as the graphs are empirical : for each gas/temp/humidity it could vary differently.
Also, don't use long wires as they could bring noise in your measurements. You don't want to detect your washing machine motor starting, do you ?
Hope this helps.