Raspberry Pi and Wireless Sensor

A few weeks ago, I blogged about at a 'shield' that plugs into the Raspberry Pi's GPIO port called the 'Slice of Pi'. This very low cost board also includes an X-Bee shaped socket into which RF modules can be plugged. The company behind the 'Slice of Pi' (Ciseco) is also behind a useful and low-cost range of RF devices.

In this blog entry, I used one of their wireless sensor modules (in this case temperature) with a pair of XRF RF modems to add remote wireless temperature sensing to the Raspberry Pi using the serial connection on the GPIO pins.

Here, a simple program (on the left) reads the temperature from the remote wireless sensor and displays it (in the right). Degrees C not F, its not that cold over here!

Hardware

Here is the Raspberry Pi, with a Slice of Pi and an XRF module all plugged together sandwich style.

I plugged them together with the Pi turned off, as 'hot-swapping' makes me nervous.

The wireless temperature sensor is made up of two modules, the temperature sensor module, complete with Lithium battery, and another XRF module -- the same as the one attached to the Pi. These just plug together.

Software

The temperature module sends the temperature as a string every 15 seconds. So all that is required of the Raspberry Pi is to catch the serial messages and display them in a Tkinter window. The sensor is microcontroller-based and quite smart, so you can do much more complicated things, including multiple sensors, sensor IDs and messages that indicate that the buttons on the sensor have been pressed.

The Python program to do this is listed in full below (20 lines of code). It requires the PySerial library which you must install. See the instructions in my earlier post  on linking the Pi to an Arduino.

From IDLE (use Python 2 not 3) select File->New and paste in the code below, then click 'Run Module'.


from Tkinter import *
import serial
import time

DEVICE = '/dev/ttyAMA0'
BAUD = 9600

root = Tk()

def updateTime() :
    ser = serial.Serial(DEVICE, BAUD)
    n = ser.inWaiting()
    if n == 4 :
        msg = ser.read(n)
        v.set(msg)
    ser.close()
    root.after(2000, updateTime)

v = StringVar()
Label(root, textvariable=v, font=("Helvetica", 240)).pack()
v.set('--.-')

root.after(2000, updateTime)
root.mainloop()



Conclusion
These are great modules with long range and low power consumption. For the full specs, visit Ciseco's website.

Thanks
Thanks to Ciseco for lending me the hardware - I will send it back, I promise!

                                                                                                                           

About the Author
These are my books. Click on the image below to find out more about them.