Get the essentials and then pick and mix your favourite sensors.
« Back Step 2 »You can buy a Raspberry Pi here.
Connect your RPI to power from the mains with one of these; if you wish to make your AirPi portable, you can attach a rechargeable battery pack such as this one. Alternatively, you could power it from a solar panel in your garden.
An internet connection can be supplied either via an Ethernet cable or a simple USB WiFi adapter which you plug directly into the Pi.
We strongly recommend connecting your Pi to the internet, otherwise you won't be able to upload any of your pi's data and view it remotely.
You may want a screen to connect to your AirPi in order to view its measurements while offline. Note that the AirPi can be configured to start automatically and upload data to the internet as soon as it is switched on, so a screen is not necessary to control it.
These are a must: you plug your sensors into breadboards to make the necessary circuits. They're reusable and you can purchase them relatively inexpensively from Oomlout, or any other electronics supplier.
The number you will need will vary depending on how many sensors you are connecting to your AirPi. We recommend starting with 1, and adding another for every 3 sensors you will use (For example, with 6 sensors you'd need 3 breadboards).
You will need a fair number of wires to plug into the breadboard to hook up all the sensors. One option is to buy a roll of wire and a wire stripper, and roll your own. This ends up being cheaper in the long run, but for this project you can buy a package of many different coloured and different length jumper wires (recommended) from Oomlout.
There are two ways to go about this, either via Adafruit's spectacular Cobbler (which does require soldering together, but makes life a lot easier afterwards), or by manually connecting the pins on the Pi to the breadboard with these female-to-female jumper leads.
You will need several resistors for different purposes in this project, they will be of different values depending on which sensors you are using; for example, to protect LEDs, or to control what voltage the sensors receive from the Pi.
You can either purchase a kit of resistors which should contain all the ones you need here or you can buy them individually from Maplin or another electronics supplier.
Many of the sensors used in this project output an analogue signal. The Raspberry Pi cannot read these signals directly, so to convert these signals to digital, you need an ADC (analogue to digital converter). I recommend the MCP3008 which has 8 separate analogue inputs, so you only need one in order to read the values for all your sensors. It can be purchased cheaply from Farnell in the UK.
If you want to run your AirPi headless (without a screen) then you may wish to purchase some red and green LEDs so your Pi can tell you once its uploaded data. We used a red LED to indicate a failure (for example, no internet), and a green one to indicate success.
The DHT22 sensor is available in the UK from Proto-Pic in the UK, or sellers on eBay for less than half the cost, but with longer shipping times. It measures both relative humidity and temperature, however we discovered that it does not measure temperatures below 0 degrees Celsius. For this reason, we recommend using the BMP085's temperature sensor (listed below), and only using the DHT22 for its relative humidity output. The DHT22 sensor is digital, so it doesn't need an ADC.
The BMP085 sensor measures both barometric pressure and temperature. Whilst calibrating the sensors, we discovered that the BMP08's temperature sensor is slightly more accurate than the DHT22's sensor, and it goes below 0 degrees as well. This sensor is also digital, and so does not require an ADC. It is available from Proto-Pic in the UK, or many different Chinese sellers on eBay for a third the cost but longer shipping times.
Although this sensor is cheap, it's hard to set up. On top of the ADC, it requires an operational amplifier (available for a pound or two), a capacitor and a number of resistors to function. Last time we checked, it can be bought here.
An LDR (Light Dependant Resistor) is a sensor which changes its resistance depending upon the light level shining upon it. These are extremely cheap and can be obtained easily from any electronics shop. The output given is analogue, so you will need an ADC (see above) to convert it to digital.
This sensor responds to various gases associated with poor air quality and the presence of smoke including methane, iso-butane, ethanol and hydrogen. It is available from RS Components. It consists of a 4 pin canister, 2 of which power the heating element for it (5V), and 2 of which are the connections to the sensing resistor (its resistance is proportional to the air quality). However, the output given by this sensor is analogue, so you needs an ADC (see above) to use it properly.
This sensor measures the concentration of NO2 in the air. It is available for approximately £5 from Component Distributors Inc. It is packaged in approximately the same form factor as the TGS 2600, with the same connections, however it is powered by 1.7V, not 5V. Similarly, the output given is analogue so an ADC (see above) is needed to use it.
This sensor measures the CO concentration in the air. It is available for £7 from Component Distributors Inc . It is packaged like the TGS2600, and the heater for it is powered by 2.4V.