Saturday, 22 March 2014

mfNordic library released on Codeplex

As part of the development effort for the home monitoring system I implemented a .net micro framework library for interfacing to a Nordic semiconductor NRF24L01P radio module. I have released the source code on under the MS-PL license.

Using the library

var radio = new Nrf24L01P(SPI_Devices.SPI1, Pins.GPIO_PIN_D0, Pins.GPIO_PIN_D1, Pins.GPIO_PIN_D2);

The Nrf24L01P class needs the SPI port, the chips select, chip enable and interrupt line that the physical radio device is connected too.

The radio can be left with the default settings or can be configured via properties. Below are some example properties.

 radio.Features = radio.Features | Feature.AckPayload | Feature.DynamicPayload;
 //Note the number of address bytes must match the configured/default radio.AddressWidth property
 radio.TransmitAddress = new byte[] {0,0,0,0,0};
 radio.Mode = Mode.Receiver;
 radio.Channel = 125;

The class will raise events when data is transmitted or received or errors occur. These events can be hooked, each has an event argument that contains relevant context information.

 _radio.OnDataReceived += RadioOnDataReceived;
 _radio.OnTransmitFailed += RadioOnTransmitFailed;
 _radio.OnTransmitSuccess += RadioOnTransmitSucess;
 _radio.OnDataReceiveFailure += RadioDataReceivedFailure;

 static void RadioDataReceivedFailure(object sender, DataReceiveFailureEventArgs e)
  Debug.Print("OnDataReceiveFailure occured on Pipe: " + e.Pipe);

 static void RadioOnDataReceived(object sender, DataReceivedEventArgs e)
  Debug.Print("RadioOnDataReceived occured on Pipe: " + e.Pipe + " " + e.Payload.Length + "bytes received");

The NRF24L01P supports up to 6 logical radio data pipelines, all sharing some basic settings namely:

  • CRC enabled/disabled (CRC always enabled when Enhanced ShockBurst™ is enabled)
  • CRC encoding scheme
  • RX address width
  • Frequency channel
  • Air data rate
  • LNA gain

The library exposes the data pipelines via an indexer. This allows properties and methods of individual pipes to be accessed.

 radio[Pipe.Pipe0].AutoAcknowledgment = true;
 radio[Pipe.Pipe0].DynamicPayload = true;
 radio[Pipe.Pipe0].Enabled = true;

Acknowledge packets can be queued on a given pipe line using the QueueAcknowledgePacket method.

 radio[Pipe.Pipe0].QueueAcknowledgePacket(new byte[] {0,1,2,3});

In transmitter mode packets can be transmitted using the Transmit method. The Boolean parameter indicates if the packet should be transmitted with an expected acknowledge from the receiver.

 radio.Transmit(new byte[] { 0, 1, 2, 3 }, false);

Finally to power the radio devices RF section up.

    radio.PowerUp = true;

To enable the  radio device, which will set the CE signal to the device, which will active the RX or TX mode of the radio device.

 radio.Enable = true;

Wednesday, 19 March 2014

Home Monitoring System – Version 1.0

Having worked on my home monitoring system on an off for the last number of weeks I have finally gotten to version 1 for the host board and the sensor nodes.

Temperature And Humidity Sensor Node

I completed the development and testing of the wireless temperature and humidity sensor nodes.


This board was installed in an enclosure as shown below. The board was designed to fit snuggly into the enclosure which takes two AAA batteries to power the sensor.


The sensor implements a simple channel scanning and handshake protocol which allows it to determine the radio frequency channel the wireless hub is listening for packets. When the channel is found by sending a NodeHello packet to which the wireless hub replies with a NodeHelloAck packet. The NodeHelloAck packet contains configuration data that the node uses to setup it logical RF channel.

Once the handshake has completed the node enters a loop where it sleeps for a period, which is provided as part of the handshake data, wakes up and transmits the latest temperature, humidity and battery voltage readings to the wireless base station.

Wireless Hub

I chose a Netduino Plus 2 as the hardware for the wireless hub. The hardware setup is pretty straight forward. An NRF24L01P radio module is connected to power and the SPI port on the Netduino.


The Netduino implements a simple web server, based on embeddedwebserver, that hosts a set of pages that renders the sensor data from each of the sensors, allows configuration changes to be made and log file viewing. Since the Netduino has limited memory and CPU most of the processing for data rending is offloaded onto the browser. The sensor data page uses a JavaScript graphing component called Rickshaw. The pages are rendered on the client side browser as a single page application using AngularJs as the MVVM framework and Bootstrap to provide a responsive UI that scales to different device screen sizes.

Sensor Data Display


The sensor data is rendered on the main page of the application. The interface allows selection of a number of days of data. Multiple sensor feeds can be rendered, the graphing component supports hoover details when the mouse is over a point on the graph.

Nodes Configuration


The nodes configuration page shows active nodes and the node types. The nodes name can be modified.

System Log


The logging level is set on the configuration page from 0 to 4, 0 = None 4 = Debug



The configuration page allows the following to be configured:

  • The radio channel
  • The radio device address
  • The log level
    • None
    • Info
    • Warn
    • Error
    • Debug
  • Update interval, the rate that the sensor will push readings

Future Additions

  • Minor web UI clean up and changes
  • The ability to export sensor data
  • The ability to have a node release its allocated id

I would also like to add some additional sensor types, maybe air quality, water,power etc. Later I would like to use the data gathered to directly control the space heating from the netduino, via a relay node that can be used to advance and retard the heating system based on evaluation of the temperature data. For example on a very cold day fire up the heat at an earlier time than the heating control system would normally.