Sensor Workshop: Datalogging
For our Datalogging assignment, Lia and I chose Parallax’s CH4 (methane) Sensor Module. The module is specifically designed to determine whether a preset level of methane gas is surpassed. The module uses a MQ-2 methane sensor, which, when heated by an applied voltage (5V), reduces its internal resistance, and hence its output voltage, in relation to the level of methane gas present in the air. The module provides circuitry to set a trigger voltage to sound an alarm for when a specific level of methane is surpassed. For this assignment, we ignored the alarm circuitry and monitored the output voltage of the sensor.
The majority of methane in Earth’s atmosphere is sourced from human activity. Natural gas, livestock “emissions”, and landfill decomposition are the largest contributors in the US. For our assignment, Lia and I were hoping to get noticeable readings from our sensor from the human emissions in the bathroom’s of Tisch.
For our assignment, we used an Arduino to both supply the voltage for the heater and read the voltage output from the sensor and we used Adafruit’s Micro-SD breakout board to record our data. We used the SD library supplied by Adafruit and modified the Datalogging sketch for our setup.
+5V->+5V (supply voltage for heater)
GND->GND & HSW
Unfortunately, we were unable to get a responsive reading from the bathrooms in Tisch and resorted to sensing the methane level at my apartment. We sampled from the livingroom, the deck, and the kitchen near to my gas stove at 1s intervals over the course of 35 minutes (allowing the sensor to warm up over the first 10 minutes).
The first 10 minutes of data from each reading were removed (these readings fluctuate as the sensor stabilizes). As the sensor is sensitive to temp, the data mostly reflects the change in temperature at each location. The upward slope of the “Oven-Off” data most likely reflects the fact that the door to the deck in the kitchen was left open and shut at the beginning of the data logging (which increased the temperature of the room and, potentially, the levels of methane that may be leaking from the oven). However, since the temperature of the kitchen (with the oven off) and livingroom are approximately equal (or at least significantly closer to each other than to the deck reading, taken on a 40F day) and the “Oven On” reading (which should reveal a further increase in temperature as the oven heated the kitchen) was taken after the “Oven Off”, it is possible that there are elevated methane levels near to the gas stove.