Making a start with XBee modules

After careful choice my decision was to go for JeeNodes and Raspberry PI. Well I've started with the X Bee wireless modules! The reason being that I'd already bought a pair some months ago so rather than waste the money I'm going to start with these. It shouldn't matter too much if I design the software to be modular and allows for these to be swapped out at a later date. The image shows just how tiny they are.

XBee2 wireless module

However, to make use of them requires a power supply and an additional device to measure temperature. The operational, wireless temperature measurement XBee is pictured below.

XBee with power regulator and TMP36

Unfortunately providing power is not as simple as connecting a battery. A stabilised power supply is required and is provided by a small voltage regulator. The XBee is plugged into a socket on this device which converts the 6V from the battery pack into 3.3V required by the XBee. It also provides a means of connecting external components like the TMP36 temperature probe. This tiny probe outputs a voltage that is proportional to temperature that the XBee measures and transmits back to a base station. Here is the base station XBee.

XBee with USB connection

This XBee is fitted into an adapter that provides a USB connection for communication with a PC and  enables the many facilities and capabilities of the XBee to be configured.

The world of wireless devices seems to be going through rapid development at the moment and the choice of devices certainly becomes wider by the day; partly as the technology develops and partly as my knowledge expands. For example, the XBees cost approximately £20 each but when browsing the Maplin site these devices were found at £3.99. They are by no means the equal or same as the Xbee of JeeNode but they could possibly be useful for some very low cost applications.

Then there are products like the Sensor drone which could be a platform for future work and the RFduino which packages the Arduino with Bluetooth into a tiny package.  And these introduce the topic of which wireless technology to use. Whereas the XBee uses the same wireless spectrum as WiFi, the JeeNode uses another. Fortunately, they all tend to have their niches and a sophisticated system will probably incorporate several of them.

Raspberry Pi is the platform of choice.

Although closer to a decision on an energy monitoring system for the project house the more I research, the more I discover alternative solutions!  However, the JeeLabs JeeNode still looks favourite for the remote wireless data logging devices. The basic cost is approximately 18.50 euros but to this must be added a few extra components such as a case and battery supply. The next step is deciding on the central management system which appears to be a choice between an Arduino or Raspberry Pi based system. Both have their advantages and disadvantages. The requirement is to log readings, record in a data base and process to calculate such information as degree days from the raw data. Also important is the ability to manage the system remotely, via a browser if possible which implies TCPIP network connectivity.

The Arduino is a very popular platform designed specifically for interfacing with sensors and for controlling external devices. It is programmed through a special program, an integrated development environment (IDE) that runs on a PC. Overall very good for dedicated control applications with a large user community but I think want more flexibility than that. 

The Raspberry Pi, on the other hand, is a more general purpose platform. It runs Linux which is an operating system that is used extensively for commercial IT systems. It is a computer that can be both a development and operating environment in one and so doesn't need an external IDE. Overall, it probably has less support currently for control and management applications and looks more complex to program. That said, support information and products for the Raspberry Pi monitoring system have been found so the convenience of everything in one low cost unit is the deciding factor.

Despite an extensive range of available products one area that does not seem well covered is the packaging of the various electronic devices. The electronics will need housing in suitable cases. One intriguing solution that was found was to convert an Airwick room freshener to house a JeeNode. Details can be found here.