Nuts and Volts - January 2016

38 January 2016

will have to put a router in to relay the packets and boost the signal. Most mains powered ZigBee devices can be a router.

A router can be something as simple as a Hue light bulb. Once you add the bulb to your network, it will figure out who its neighbors are and start routing packets to them. In fact, that is how we communicate with our chicken coop door controller. We have ZigBee Hue bulbs in our landscaping that carry the traffic to our chicken coop in the back yard.

Strong Application Layer Allowing Devices to Find Each Other and Communicate

In addition to ZigBee’s strong networking layer, it also has a well-defined application layer that describes how common devices can discover each other and communicate. This is what makes ZigBee so attractive for device makers. A great deal of the common actions most devices require are categorized and defined in “cluster”

definitions. ZigBee clusters are given 16-bit numbers, often represented as hex numbers. Table 1 is a very small sample of common clusters used by devices. Cluster commands are either a server or client command. For example, say we have a ZigBee enabled light bulb and a ZigBee enabled wall switch. Both devices will communicate using the commands defined in the On/Off (0x0006) cluster. The light bulb will be the server and the light switch will be the client. How the light switch sends the “on” command and how the bulb receives the “on” command are all defined in the On/Off (0x0006) cluster specification. Why is this important to a device maker? Let’s say you want to make a device that has an LED, and you want to turn the LED on or off remotely. If your device follows the guidelines detailed by the On/Off Cluster, then your device can be controlled by the exact same ZigBee enabled wall switch discussed above. Let’s take that one step further. Replace the ZigBee enabled wall switch with a smartphone application. Say you have an existing home automation solution with a smartphone application that controls your ZigBee enabled lights (like Smart Things). Since your LED device adheres to the ZigBee On/Off cluster commands, it is now possible to control the LED by that same smartphone app! Your device just joined the Internet of Things!

You have all the power of that slick smartphone app without writing one line of custom code for your smartphone! Not only can you control your LED from your smartphone, it can also be part of your home automation. So, if you have your home automation rules set up to turn on your lights when you pull into your garage, your LED can come on as well.

Controlling a Custom Device with

SmartThings

This project is going to focus on the radio hardware setup and communications required to talk to a

ZigBee HA network hub (Smart Things) over ZigBee standard Clusters. We will use a Propeller microcontroller connected to a Digi XBee ZB radio to communicate with the hub. The circuit is simple and you can use any number of existing Propeller prototype boards. To play along, you will need some hardware. Here are a couple of options: Option 1) is a custom PCB and a link to the parts you can order to populate it (requires soldering); Option 2) is a list of parts you can order to work with one of your existing Propeller project boards (refer to Tables 2 and 3). There is an Option 1) ZB-LED PCB,