Sensors for the competetion :
As i havent received the boards, to start with I am explaining in this post the sensors used in the competetion.
Air Pollution
For air pollution I will be using MQ series of sensors. Which sensor i will use will depend on budget and availability. Here i am detailing all such sensors that I am looking forward to.
The MQ series of gas sensors use a small heater inside with an electro-chemical sensor and are sensitive for a range of gases and are used indoors at room temperature.
They can be calibrated more or less but a known concentration of the measured gas or gasses is needed for that. Typical circuit diagram is:
Heater is for +5V and is connected to both 'A' pins.
The variable resistor in the picture is the load-resistor and it can be used to determine a good value.
The Vout is connected to an analog input of the Beaglebone.
The Heater
Some sensors use 5V for the heater, others need 2V. The 2V can be created with a PWM signal and a transistor or logic-level mosfet.The heater may not be connected directly to an output-pin of the Beaglebone, since it uses too much current for that.
If it is used in a battery operated device, a transistor or logic-level mosfet could also be used to switch the heater on and off.
The sensors that use 5V or 6V for the internal heater do get warm. They can easily get 50 or 60 degrees Celcius.
After the "burn-in time", the heater needs to be on for about 3 minutes before the readings become stable.
Load-resistor
The sensor needs a load-resistor at the output to ground. It's value could be from 2kOhm to 47kOhm. The lower the value, the less sensitive. The higher the value, the less accurate for higher concentrations of gas.
If only one specific gas is measured, the load-resistor can be calibrated by applying a know concentration of that gas. If the sensor is used to measure any gas (like in a air quality detector) the load-resistor could be set for a value of about 1V output with clean air.
Choosing a good value for the load-resistor is only valid after the burn-in time.
Burn-in
It is the time to burn-in the sensor. This is meant to make the sensor readings more consistent. A time of 12 or 24 hours is usually used for the burn-in time.
The Burn-in is achieved by applying normal power to the sensor (to the heater and with the 'A' and 'B' pins connected, and with a load-resistor).
MQ-2
Sensitive for Methane, Butane, LPG, smoke.
This sensor is sensitive for flamable and combustible gasses.
The heater uses 5V.
The MQ-2 at seeed: http://www.seeedstudio.com/wiki/Grove_-_Gas_Sensor%28MQ2%29
MQ-3
Sensitive for Alcohol, Ethanol, smoke
The heater uses 5V
The Arduino blog about the "breathalyzer" using a MQ-3 : http://arduino.cc/blog/2010/09/23/arduino-breathalyzer-calibrating-the-mq-3-alcohol-sensor/
The MQ303A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ-4
Sensitive for Methane, CNG Gas
The heater uses 5V.
MQ-7
Sensitive for Carbon Monoxide
The heater uses an alternating voltage of 5V and 1.4V.
MQ-8
Sensitive for Hydrogen Gas
The heater uses 5V.
MQ-9
Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 5V and 1.5V. It depends on the gases how to use that alternating voltage. If only Carbon Monoxide is tested, the heater can be set at 1.5V.
The MQ309A (also on this page) is like this sensor, but uses a lower heater voltage.
MQ131
Sensitive for Ozone
The heater uses 6V.
The load-resistor is 100k...200k, which is a lot higher than for other sensors. This sensor is also very sensitive. It measures in ppb (parts per billion) where other sensors measure in ppm (parts per million).
MQ135
For Air Quality
Sensitive for Benzene, Alcohol, smoke.
The heater uses 5V.
An example with calculation of the CO2 value: http://davidegironi.blogspot.it/2014/01/cheap-co2-meter-using-mq135-sensor-with.html
MQ136
Sensitive for Hydrogen Sulfide gas.
The heater uses 5V.
MQ137
Sensitive for Ammonia.
The heater uses 5V.
MQ138
Sensitive for Benzene, Toluene, Alcohol, Acetone, Propane, Formaldehyde gas, Hydrogen gas.
The heater uses 5V.
MQ216
Sensitive for Natural gas, Coal gas.
MQ307A
Sensitive for Carbon Monoxide
The heater uses an alternating voltage of 0.2V and 0.9.
It detects the same gasses as the MQ-7, but uses a lower heater voltage.
MQ309A
Sensitive for Carbon Monoxide, flammable gasses.
The heater uses an alternating voltage of 0.2V and 0.9V. It depends on the gases how to use that alternating voltage.
It detects the same gasses as the MQ-9, but uses a lower heater voltage.
For Humidity and temperature sensors requirements I will be using the Sensor Hub BoosterPack from ti for it assuming the launchpads have libraries for the same on energia. The ambient light sensor will be used to complement smoke sensors of the MQ series.
