This project assumes you already have a Model A or B Raspberry Pi, power supply, HD card, screen, keyboard, network etc. Raspbian Wheezy OS.
In this project you will construct a wireless battery operated temperature sensor. The sensor communicates with the Raspberry Pi over radio frequency (RF) communications to a base station RF receiver. You can connect as many transmitters as you like (e.g. inside, outside, fridge, etc…).
What you need
The parts can be purchased from the PrivateEyePi Store
How it works
The wireless temperature sensor will transmit the temperature at 5 minute intervals to the base station. The transmitter is optimized for extremely low current consumption so that it is able to last over a year on a single set of batteries, or 1 coin cell if you are using the wireless sensor kit (RF04). The RF units are very powerful and should easily handle communications distances around a residential home. The antennae of the transmitter can be adjusted for longer distances, or for greater strength to compensation for walls or other physical barriers. The transmitters come pre-configured with a unique number identifier that will be used to uniquely identify each sensor. This enables you to have as many wireless temperature sensors as you want (e.g. inside, outside, fridge etc… ). The Python code required to read the temperatures from the serial communications stream is provided. We also provide the code to send the temperature value to the PrivateEyePi server to be displayed on your WWW dashboard; however this is not a mandatory part of this project. If you want a wireless temperature sensor for other projects then these steps will help you achieve that goal too.
The RF transmitter looks exactly the same as the receiver units so be careful not to mix them up. The packaging of the receivers and transmitters will be clearly marked so you know what is what. If you do mix them up them some trial and error testing should solve the problem.
The two white wires you see protruding on the right hand side are connected to the thermistor temperature sensor.
Figure 1 - A wireless sensor case kit with a temperature sensor attached
Alternatively you can choose to connect the thermistor directly to the coin cell board as shown in Figure 2.
Figure 2 - Thermistor connected directly to the coin cell board
That's it! Now you are ready to move on to the software section.
If you chose not to use the wireless sensor case kit you could construct the wireless sensor using your own circuitry. The tricky part is connecting wires to the pins of the RF unit as they are spaced very close together and do not plug into a breadboard. You could:
Figure 3 shown the circuit diagram and figure 4 shows you the pin numbers on the RF transmitter.
Figure 3 - Wireless Temperature Sensor
Figure 4 - Pin-outs for the RF Modules