1. Peter Hardy
  2. RF24SensorNet




This library defines a collection of sensor and actuator types, and provides a convenient way to send data and commands to/from them using RF24Network as a transport.


This library relies on the RF24 and RF24Network libraries. There are several forks, but I'm regularly running it against TMRh20's code: RF24, and RF24Network.

I've also tested against maniacbug's original RF24Network library.

The MqttRelay sketch also uses the pubsubclient library.


The network consists of several nodes, each consisting of an Arduino-compatible MCU and an nRF24L01 radio module. Each node can have zero or more devices of the below types connected, each with a unique ID.

There are three basic message types:

  • A request for data from a device. This request will contain the destination node address, the device type, and the device's ID.
  • A request to send data to a device (for example, turn a switch on). The request will contain the destination node address, device type, and other information depending on the device.
  • A device data packet. It will contain the destination node address, device type, and other information depending on the device. It can be sent in response to either of the above request messages, or on any type of schedule defined by the sending node.

All messages sent across the network are one-one.

Supported device types

  • info. Used to retrieve information about a node, including the status of all attached devices.
  • power. Used to retrieve information about a node's power supply. Can be used to show battery status, or how much power is being supplied by an attached solar panel.
  • switch. A basic digital on/off switch. This can be used to switch relays attached to a node on and off, or a node can use it to report status of an attached switch.
  • rgb. Sends three values for red, green and blue channels. Used to control RGB lights, or fading lights.
  • temp. A temperature sensor. Currently only supports reading/sending temperatures, so it's not (yet) suitable for controlling thermostats.
  • humid. A humidity sensor. Sends relative humidity.


The info device type is currently unimplemented. I'm intending to use it to retrieve the status of all devices attached to a node, and use it to set the node's RF24Network address.

Temperature devices are currently read-only.

Note that temperature and humidity readings are passed around on the RF24Network as integers, multiplied by 10. 15.6 degrees will be represented in the packet as 156, and 43.5% humidity as 435.

The library is currently a fair bit heavier than it really needs to be - it'll run on ATtiny processors, but some juggling might be required to get a sketch in to their 8KB of flash. Optimizing code size and rearranging to make it easier to add new device types is next on the list of things to do.


Sending messages

Each device type has three functions, to send each type of message.

  • read* sends a message requesting data from a device.
  • write* sends a message containing new data for devices that support being modified.
  • send* sends a message containing device data.

Receiving messages

A node interested in receiving messages pertaining to a given device type must implement one or more callback functions, and register them with these functions:

  • add*ReadHandler registers a callback that will receive requests for device data.
  • add*WriteHandler registers a callback that will receive requests to change a device (not all devices support this).
  • add*RcvHandler registers a callback that will receive messages containing data from a device.


  • rxTest: A basic node with a single switch device controlling an LED. Load this on an arduino with nRF24L01 module, and attach an LED to pin 5.
  • txTest: A basic node with no attached devices, which blinks a remote switch device on and off. Loat this on a second arduino with nRF24L01 module, and it will switch the rxTest module on and off.


The MqttRelay sketch runs on an Ethernet-equipped Arduino. It registers to an MQTT bus. It is designed to run with the Arduino's standard Ethernet library, and uses pubsubclient to talk to MQTT.

Before attempting to use it, you'll need to update mqttBroker, mqttClientID, mqttUsername and mqttPassword to match your network. They're towards the top of the sketch and commented.

The sketch registers as RF24Network device ID 0 - the root node. Any node on the RF24 network may address a packet to 0, and if it's a valid RF24SensorNet packet it will be relayed to MQTT.

MQTT packet format

Messages relayed from the RF24 network on to MQTT will be sent with a topic sensornet/out/*nodeAddress*/*packetType*. For a message to be relayed from MQTT in to the RF24 network, it should be sent with a topic sensornet/in/*nodeAddress*/*packetType*.

nodeAddress is the RF24Network address of the source/destination node. packetType is the sum of the device type and a command type. Device types describe what class of device is sending or recieving this packet, and are listed in the pkt_type enum in RF24SensorNet_types.h:

Type ID

The command type specifies if this packet contains device data, or a read or write request. These are:

Type ID
Device data 0
Device read request 32
Device write request 64

For example, when the node at RF24 network address 012 sends a packet about its current battery reading, it will be broadcast on MQTT with a topic of sensornet/out/12/1. If an MQTT client wants to get a temperature reading from the node at RF24 network address 03, it should broadcast an MQTT message with a topic of sensornet/in/3/36. And when an MQTT client would like to change the colour of a light attached to a node at RF24 network address 021, it should use a topic of sensornet/in/21/67.

For both inbound and outbound traffic, the MQTT payload should be the contents of the appropriate packet type, in order, delineated with pipe (|) characters. Again, these are described in RF24SensorNet_types.h. Most types are numeric. For boolean types, use 1 for true and 0 for false.

An MQTT command requesting the switch with device ID 3 be turned on will have a payload of 3|1|0. An MQTT packet with a temperature reading of 27.3 degrees from device ID 0 will have a payload of 0|27.3.