A low-power network, not Wi-Fi

The question

A temperature sensor in a wardrobe runs on a coin cell and has no Wi-Fi. A wall switch turns on a light across the room while the hub is switched off. Both work, and neither needs a router with a password. This course follows one house to show how.

The radio and the network

Two standards are in play and they are easy to blur. IEEE 802.15.4 defines a low-rate, low-power radio. Zigbee defines a network and an application on top of it: who forms the network, who forwards, how a device is named and what a light can be asked to do. The radio is one thing and the network is another.

Wi-Fi uses the same 2.4 GHz band for a different network. A Wi-Fi laptop cannot join a Zigbee network, and a Zigbee light cannot join Wi-Fi. They share the air and nothing else.

What is on the bench

The house has a wall switch, two lights, a smart plug configured as a router, a door sensor, a battery temperature sensor and a coordinator dongle. The computer the dongle is plugged into is the host. It is not the coordinator.

Each value on the benches wears one of three labels. Protocol is what the standard defines, such as a role. Reported is what a real stack would tell a controller, such as a signal reading. Example is a teaching input with no universal value, such as what a wall costs in decibels.

The drawing is placement, not coverage. Whether two devices hear each other is an estimate, with its assumptions beside it, and a wall costs decibels without being a hop.

Where this goes

The next lessons take the network apart: the shared radio, the three roles, names and addresses, joining, paths, a sleeping device and its parent, what a device can do, security, the controller side, failure, and the ESP32 on the bench. The last lesson hands over to the Zigbee, Thread and Matter chapter of the ESP32 book.

Common mistakes

• Treating Zigbee as a slow Wi-Fi. It is a different network on a different radio standard. Sharing a band is not sharing a network.
• Reading the drawing as coverage. The house shows where things are installed. A link is a conditional estimate from the whole budget.
• Calling the host the coordinator. The coordinator is a radio role. The computer running the controller software is something else.