Thursday, August 23, 2012

Wireless Sensor Networks - a review of devices


Photo:  the emonGLCD by openenergymonitor.org

The second part of a post reviewing what is available to the hobbyist in terms of open source hardware for wireless sensing networks.  This time I look at a series of kits that are compatible with the JeeNode from JeeLabs.

One of the key design challenges with any modern electronic device is the age-old problem of how do you get the power in and the data out?  A bi-directional low power wireless link solves the second of these problems, and innovative use of low power electronics, rechargeable batteries and possibly a tiny solar PV panel solves the first.

So with a low power microcontroller and a short range wireless transceiver you have the basis of a smart wireless node – which can be used for a variety of sensing on control applications.  The ability for it to communicate with web connected devices – via the wireless to Ethernet bridge opens up a vast number of possibilities for remote sensing and control. With the availability of open data services – such as Open Energy Monitor and Cosm, there is an easy route to get sensor data up to Cloud based servers from where it can be processed, graphed or mapped using appropriate data manipulation tools.

Having decided in principle upon a simple Ethernet to Wireless bridge, then comes the task of supporting a range of diverse wireless nodes. Range tests have shown that the RFM12 has a useful range of 100m in the household environment, opening up a whole host of possibilities for wireless energy monitoring, central heating control, solar pV monitoring or other wireless gadgets that just need to get a few bytes of data up to a central server.

Through suppliers such as JeeLabs, Open Energy Monitor, Wicked Device and Nanode Ltd there are starting to become available a wide range of compatible wireless devices aimed at low cost wireless sensing and control applications. These devices all use the RFM12 library code as developed by JeeLabs for the JeeNode, and generally devices from different vendors may be mixed and matched.
A short summary of some of the devices.

JeeNode



The original wireless node by Jean Claude Wippler of JeeLabs.  A simple combination of an ATmega328 microcontroller and RFM12B wireless transceiver on a small pcb.  JeeNode utilises the concept of 4 identical ports into which a wide variety of functional modules can be plugged to extend the basic system.  For full details see the comprehensive JeeLabs site.

emonTx

A development of the basic JeeNode, designed specifically for electricity monitoring applications.  It has 3 current transformer interfaces, and voltage, pulse and temperature inputs. emonTx forms the basis of the Open Energy Monitor – see OEM website for more information.  

emonGLCD

One  useful kit, is the emonGLCD wireless graphical display from Open Energy Monitor. This consists of a 128 x 64 pixel graphic LCD with an ATmega328 and the Hope RFM12 wireless transceiver. Whilst originally designed to display data from the energy monitor, the GLCD may be used to display any data – either that generated locally, or generated from a web based application.  The versatile GLCD has three user push buttons “Up”, “Down” and “Enter” allowing the user to select items or parameters from a menu an modify them, or select particular modes. My first intended application for the GLCD is as a user interface for a smart central heating controller.

In addition to the user push buttons, the GLCD has a LED backlight, a bicolour LED to show for example the status, and a LDR light sensor.  The LDR may be used to determine whether it is day or night, or whether the room lights are on – suggesting that the room is occupied.  To complete the usefulness of the device, an on board 18B20 temperature sensor allows the room temperature to be measured, allowing the GLCD to be used immediately for smart thermostat applications.  As with all the wireless devices offered by Open Energy Monitor, the GLCD is firmware compatible with JeeNodes, Nanode RF and WiNode.

WiNode

WiNode is the first standalone wireless sensor device from Nanode Ltd.  It is aimed at wireless sensing and control applications, and has a number of features not found on other devices.

1.  Motor driver IC for driving 2 motors, 4 relays or even a loudspeaker. Accessible via screw terminals.

2.  4 general purpose analogue inputs with voltage scaling networks. Accessible via screw terminals. Could be used for current transformers or opto-reflective pulse counters (gas meter)

3.  microSD card – for datalogging or file storage. Can be used to store audio files for playback via loudspeaker

4.  32K battery backed SRAM – retain data during a power outage

5.  Real Time Clock and Calendar with alarm wake-up function.

Air Quality Egg - by Wicked Device

This is a new development this year from our friends at Wicked Device and Sensemakers/Cosm.


Photo: Wicked Device.

On the right is the new Nanode RF SMT - by Wicked Device.  This is a much updated and improved version of the Nanode RF manufactured almost exclusively using SMT components.  The Nanode RF includes a 433MHz low power wireless transceiver and ENC28J60 ethernet controller.  Plug in headers allow Arduino type shields to be added to extend the system.

On the left is a stripped down Nanode RF - fitted with the Air Quality Egg sensor shield - a series of plug in gas sensors to allow measurements of typical air pollutants to me measured and sent up to a open data server - provide by Cosm.
















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