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 build a wireless base station receiver that can receive communications from a multiple wireless sensors like a temperature sensor, door contact or motion sensor. The wireless sensors communicate with the Raspberry Pi over radio frequency (RF) communications to a base station receiver. You can connect as many wireless sensors as you like.
You will be using the XRF wireless module from CISECO that operates at the 868 and 915 MHz ISM/SRD bands (but can also support 315, 433, 900 MHz). These modules are very flexible and can have different firmwares loaded onto them allowing them to take on different personalities. You can read further about the firmware versions and how to upload them here. We pre-load the modules with the correct firmware so you do not have to load the modules yourself unless you want to change the personality yourself.
The wireless communications are encrypted and the are very powerful. The modules should easily handle communications distances in and around a residential home. The antennae of the transmitters can be adjusted for longer distances, or for greater strength to compensate for walls or other physical barriers making them perfect for home security. The range of can be over 1 mile unobstructed.
What you need
The RF parts can be purchased from the PrivateEyePi Store
How it works
The wireless sensors (like the wireless temperature sensor, wireless switch and motion sensor) transmit their signals to the base station which interfaces directly with the Raspberry Pi serial port. You will use the Python scripts we provide to monitor the serial port and process the data coming in from the sensors. The base station receiver operates on the power of the Raspberry Pi so does not need an external power source. You do not need to know anything about RF communications or serial communications in order to do this project.
Start by constructing the Slice Of Pi, which is very straightforward. Just solder in the 5 headers as shown in figure 1. The 26 pin header (facing down in Figure 1) connects the board to your Raspberry Pi. The two headers on the left of the picture allow access to the GPIO pins of the Raspberry Pi using jumper wires, and then the two headers connected to the feet of the RF module allow you to easily plug in and out RF modules.
All the XRF units look exactly the same 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.
Figure 1 - Slice Of Pi with the Wireless Base Station Receiver
That's it! Now you are ready to move on to constructing your wireless sensor.
If you have chosen to construct your own circuitry then connect the RF modules to the GPIO header on the RaspberryPi as shown in Figure 2. 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. To solve this problem its a good idea to solder wires to a 2mm 10 way header that plugs into the RF unit. This prevents you from having to solder directly to the RF receiver.
Figure 2- Wireless Base Station Receiver