These nodes typically employ a communication device and a recording device (or gateway) and no sensors. They’re used to collect data from one or more data or sensor nodes.
In the examples discussed thus far, the monitoring system would have one or more aggregator nodes to read the data from the sensors.
The figure shows how each type of node would be used in a fictional sensor network.
For the more general case, the diagram should probably show multiple data nodes (so that the aggregator node is actually aggregating stuff).
In this example, several sensor nodes at the top send data wirelessly to a data node in the middle. The data node collects the data and saves it to a secure digital card, which then sends the data to an aggregator node that communicates with a database server via a wired computer network to store the data.
Mixing data nodes with aggregator nodes ensure that you won’t lose any data if your aggregator node fails or the recording and monitoring the system fails or goes offline.
Now that you understand the types of nodes in a sensor network, let’s examine sensors: how they can measure data, and examples of sensors available for building low-cost sensor networks.