Calibrating your CH4 Methane sensor is pretty easy. Time to get your multimeter out and sniff some farts.



Your sensor comes in the mail in two pieces; 1) the sensor and 2) the Parallax breakout board. The sensor puts out resistive data so it can be plugged into the breakout board either way. But if you're the type who likes to read it for yourself, here's the data sheet (read under, "Connecting and Testing," and, "Calibrating");

http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/27930-1-2-GasSensor-v2.1.pdf



Work to do on your sketch:

Download my CH4calibration sketch linked below. Pretty much all it does is make Arduino pin7 your HSW pin, make it an output and set it to low (which turns on your sensor's heater).



Work to do on your Breadboard:

Plug your Methane sensor into your breadboard:

ALR is your Alarm and will be left alone while we calibrate your sensor

HSW is the heater of your gas sensor, connect it to Arduino pin7

+5v is power in, connect it to Arduino 5V

GND is ground, connect it to Arduino Gnd



Calibrate:

Get yourself to a clean-air environment (fart free), upload the sketch to your Arduino and set an egg timer for 10 minutes. You need to let the heater warm up and the sensor "settle" before you begin calibrating.

When you come back in ten minutes you should have a warm-to-the-touch sensor.

Set your multimeter up to read DC voltage and hold the test terminals to test points 3 and 4 (labeled TP3 and TP4 on the left edge of your breakout board). You're hoping to read 0.80 Volts. If you're too low, turn the potentiometer labeled "TRIP LEVEL" counter-clockwise until you get as close to 0.80 Volts as possible.

Once you've got your TRIP LEVEL calibrated to 0.80 Volts it's time to read the voltage across test points 1 and 2. Again, we're looking for something around 0.80 Volts. Adjust the potentiometer labeled "SET POINT" up to about 0.80 Volts until the red LED (located at the top, left of the breakout board just under the silk screened "CH4" label) lights up. This LED lights up when the voltage from your Set Point is greater than the voltage from your Trip Level. If this LED is lit then it's ALR pin will be sending a signal HIGH, which we will later attach to Arduino Pin2 because that's the input pin we're using as our trigger. Now turn your Set Point potentiometer clockwise until the red LED just turns off.



OK, so now you have a calibrated CH4 Methane sensor with the red LED off. Look over your shoulder to make sure you're still the only person in the room and... fart on your Arduino. Wait for it... WAIT FOR IT... and the red LED turned on! Hurray, you've done it, your CH4 Methane sensor is calibrated! If the LED didn't turn on then we've got troubleshooting to do.



Troubleshooting:

If your red LED didn't turn on it's because the voltage from your Set Point didn't go higher than the voltage from your Trip Level. Check the voltage across test points 3 and 4. If you're at 0.80 Volts we're OK. Check the voltage across test points 1 and 2. You'll show something less than 0.80 Volts... there's your problem. Get yourself into a clear-air environment and turn the Set Point potentiometer counter-clockwise until you're just under 0.80 Volts. Fart on the sensor and you should see the red LED light up. Still no red LED? We've got one last way to fix that.

If you're still not getting enough voltage from your Set Point, then we'll have to lower the voltage from your Trip Level. I'd like to take a moment to tell you, that while this will work, it'll also make your sensor more sensitive so you'll have to increase the debounce delay at the end of the void_loop in the final sketch. To decrease the voltage across your Trip Level, turn your Trip Level potentiometer clockwise until your red LED turns on in a clean-air environment. Then turn it counter-clockwise until the red LED just turns off.



** If you can't muster a fart or two, the data sheet recommends using Propane as a Methane substitute **

