ZigBee, WiFi and Bluetooth

ons maj 11, 2011 (Axcon)

The drive towards wireless devices and replacing cables with wireless connection has definitely increased the number of short range RF solutions being developed. It’s been the talk for a long time, but based on our experience from the designs we are involved in, this is very much the case now.

Any short range wireless design will have to look at ZigBee, WiFi, Bluetooth and other competing solutions – including the Danish Z-wave. Many designs actually implement multiple wireless radios in a very small area.

This brings up an interesting question, since all these wireless standard operate in the license free ISM bands: will the radios interfere too much?

The ZigBee standard

The ZigBee technology is focused on connecting devices together with low cost and low power consumption. The communication is based on IEEE standard 802.15.4 and communicates on 2.4GHz. The transfer rate is up to 250kbit/s.

There are multiple commercially available products using ZigBee technology, mostly in home automation and remote control applications.

ZigBee implemented in the corner of a board, with the antenna (the “L”-shaped structure) laid out as part of the board. The foot-print for a programming adaptor and SMA connector for testing are still on the board, as this was useful in development.

The Bluetooth standard

Another wireless standard with slightly higher power consumption, more complexity, higher data rate and lower range – and most importantly: can talk to most mobile phones. This was exactly why that was the wireless standard of choice for the wireless door lock, that would automatically unlock the door as the person approached it.

Bluetooth is easily implemented using small - but functionally very similar - modules. This picture shows some of the many modules we tested for the door lock project.

One big advantage in using a module is reduced testing and approval work for the radio.


WiFi is many things

The rapid development of anything related to PC technology is a constant challenge to all embedded systems, as the technology life spans may not match very well. This is also true for WiFi, which is so well known and widespread, that further introduction is unneeded. Worth noting however is, that the standard has and is evolving with higher speed being the primary objective. There are now a whole range of standards under the common hat of IEEE 802.11 – luckily most radio implementations cover multiple standards in one device.

The picture shows a very flexible WiFi solution implemented on a printed circuit board.

The picture shows a very flexible WiFi solution implemented on a printed circuit board.


ZigBee and WiFi in one box?

A recent project we did had exactly this potential issue. To imagine the product, think of two devices each about the size of a lunch box. One device is the display and smartness, with Windows CE, .NET based user interface, touch screen and all it takes to create a modern user interface in a rugged system. The other device is more simple, with some mechanical actuators, motors and a wireless link to the display unit.

The short link between the two boxes was implemented using ZigBee. Low data rate, low power consumption and very robust radio performance, were the primary reasons. The longer link between a wireless router, the internet, a server and the display box was implemented using WiFi for obvious reasons.

This put the ZigBee radio and the WiFi radio on the same board and within a fairly short distance. Numerous tests in the lab and in real life scenarios show this to be working very well and robustly. If your project calls on any combination of wireless radios, be careful but optimistic. It will most likely work well, but seek advice before you go to far.

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