In all XBee networks, it is important that the modules involved agree on the settings that define how they communicate. The default configuration of a Series 1 XBee module is to use peer-to-peer mode. In that mode, all modules must be configured by the user, in advance, using a tool such as XCTU to matching PAN ID (ID) and channel (CH) settings. In peer-to-peer mode the radios must be available to communicate at all times, so must always be awake and fully powered.
In this activity, the radios are mobile and may not have a power outlet nearby. While they could still be used in peer-to-peer mode, this would use more power. In what is known as NonBeacon mode, it is possible for some of the modules to sleep, thus consuming significantly less power.
In NonBeacon mode, there is one node which must remain powered at all times so that it can be available to the sleeping nodes whenever they wake up. This node is the coordinator. In this example we have made the seeker the coordinator by specifying CE = 1 for that device.
No longer must the nodes of the network agree on a common ID and CH in advance, they can be configured to get missing information from a coordinator in a process called association. The A1 setting (on the end devices) and the A2 setting (on the coordinator) determine which information the modules will use to find a coordinator to associate with. With the A1 and A2 settings configured in this example the PAN ID is determined in advance by explicitly specifying a value for the ID parameter. The coordinator and end devices will determine the channel without needing CH to be configured on either.
The SM value tells the end device that it can sleep. Radios can sleep in a number of ways, but the one used here is on a simple periodic schedule. The SM value tells the radio to perform "Cyclic Sleep" as determined by the ST and SP values.
|title||The coordinator must always be powered.|
The coordinator must always be powered. By adjusting the sleep settings, you can make a configuration where the hiding unit can remain hidden and operational for long periods of time efficiently. Only power the seeking unit when playing for the longest battery life.