Wireless field gateway protocol V2

I have now built a couple of nRF2L01P field gateways (for AdaFriut.IO & Azure IoT Hubs) which run as a background tasks on Windows 10 IoT Core on RaspberyPI). I have also written several clients which run on Arduino, devDuino, Netduino, and Seeeduino devices.

I have tried to keep the protocol simple (telemetry only) to deploy and it will be used in high school student projects in the next couple of weeks.

To make the payload smaller the first byte of the message now specifies the message type in the top nibble and the length of the device unique identifier in the bottom nibble.

0 = Echo

The message is displayed by the field gateway as text & hexadecimal.

1 = Device identifier + Comma separated values (CSV) payload

[0] – Set to 0001, XXXX   Device identifier length

[1]..[1+Device identifier length] – Unique device identifier bytes e.g. Mac address

[1+Device identifier length+1 ]..[31] – CSV payload e.g.  SensorID value, SensorID value


Wireless field gateway devDuino client V1

This client is a devDuino V2.2 device with an AdaFruit AM2315 temperature & humidity sensor. This sensor is powered by two AAA batteries and has an on-board support for unique device identification and encryption.

In this first iteration the focus was accessing the SHA204A crypto and authentication chip, the AM2315 sensor and message payload assembly. Reducing the power consumption, improving reliability etc. will be covered in future posts.

Copyright ® 2018 Jan devMobile Software, All Rights Reserved


You can do what you want with this code, acknowledgment would be nice.


#include <RF24.h>
#include <Adafruit_AM2315.h>
#include <sha204_library.h>

// nRF24L01 ISM wireless module setup
RF24 radio(7,6);
const int nRFPayloadSize = 32 ;
char payload[nRFPayloadSize] = "";
const byte FieldGatewayAddress[5] = "Base1";
const byte FieldGatewayChannel = 10 ;
const rf24_pa_dbm_e RadioPALevel = RF24_PA_MAX;
const rf24_datarate_e RadioDataRate = RF24_250KBPS; 

// ATSHA204 secure authentication, validation with crypto and hashing (initially only used for unique serial number)
atsha204Class sha204(A2);
const int SerialNumberLength = 9 ;
uint8_t serialNumber[SerialNumberLength];

// AM2315 I2C Outdoors temperature and humdity sensor
Adafruit_AM2315 am2315;

const int LoopSleepDelay = 30000 ;

void setup()
  Serial.println("Setup called");

  // Retrieve the serial number then display it nicely

  for (int i=0; i<SerialNumberLength; i++)
    // Add a leading zero
    if ( serialNumber[i] < 16)
    Serial.print(serialNumber[i], HEX);
    Serial.print(" ");

  // Configure the AM2315 temperature & humidity sensor
  Serial.println("AM2315 setup");

  // Configure the nRF24 module
  Serial.println("nRF24 setup");
  radio.setDataRate(RadioDataRate) ;


  Serial.println("Setup done");

void loop()
  float temperature ;
  float humidity ;
  float batteryVoltage ;

  Serial.println("Loop called");
  memset( payload, 0, sizeof( payload));

  // prepare the payload header
  int payloadLength = 0 ;
  payload[0] = 1 ; // Sensor device unique ID header with CSV payload
  payloadLength += 1;

  // Copy the ATSHA204 device serial number into the payload
  payload[1] = SerialNumberLength ;
  payloadLength += 1;
  memcpy( &payload[payloadLength], serialNumber, SerialNumberLength);
  payloadLength += SerialNumberLength ;

  // Read the temperature, humidity & battery voltage values then display nicely
  am2315.readTemperatureAndHumidity(temperature, humidity);
  Serial.print( temperature, 1 ) ;
  Serial.print( "C" ) ;

  Serial.print(" H:");
  Serial.print( humidity, 0 ) ;
  Serial.print( "%" ) ;

  batteryVoltage = readVcc() / 1000.0 ;
  Serial.print(" B:");
  Serial.print( batteryVoltage, 2 ) ;
  Serial.println( "V" ) ;

  // Copy the temperature into the payload
  payload[ payloadLength] = 'T';
  payloadLength += 1 ;
  dtostrf(temperature, 6, 1, &payload[payloadLength]);
  payloadLength += 6;
  payload[ payloadLength] = ',';
  payloadLength += 1 ;

  // Copy the humidity into the payload
  payload[ payloadLength] = 'H';
  payloadLength += 1 ;
  dtostrf(humidity, 4, 0, &payload[payloadLength]);
  payloadLength += 4;
  payload[ payloadLength] = ',';
  payloadLength += 1 ;

  // Copy the battery voltage into the payload
  payload[ payloadLength] = 'V';
  payloadLength += 1 ;

  dtostrf(batteryVoltage, 5, 2, &payload[payloadLength]);
  payloadLength += 5;

  // Powerup the nRF24 chipset then send the payload to base station
  Serial.print( "Payload length:");
  Serial.println( payloadLength );


  Serial.println( "nRF24 write" ) ;
  boolean result = radio.write(payload, payloadLength);
  if (result)
    Serial.println("Write Ok...");
    Serial.println("Write failed.");

 Serial.println( "nRF24 power down" ) ;


Arduino monitor output


Prototype hardware

devDuinoAM2315V1Bill of materials (prices as at Jan 2018)

  • devDuino V2.2 USD18
  • AdaFruit AM2315 USD30
  • Grove – 5cm buckled cable USD1.90
  • Grove – Screw Terminal USD2.90
  • 10K resistors x 2

RaspberyPI UWP application diagnostic output

Interrupt Triggered: RisingEdge
Interrupt Triggered: FallingEdge
09:39:03 Address 01-23-32-66-C6-FE-0B-8D-EE Length 9 Payload T  25.0,H  48,V 3.31 Length 20
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-T Value 25.0
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-H Value 48
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-V Value 3.31
Interrupt Triggered: RisingEdge
Interrupt Triggered: FallingEdge
09:39:33 Address 01-23-32-66-C6-FE-0B-8D-EE Length 9 Payload T  24.9,H  48,V 3.30 Length 20
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-T Value 24.9
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-H Value 48
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-V Value 3.30
Interrupt Triggered: RisingEdge
Interrupt Triggered: FallingEdge
09:40:04 Address 01-23-32-66-C6-FE-0B-8D-EE Length 9 Payload T  24.9,H  48,V 3.31 Length 20
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-T Value 24.9
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-H Value 48
 Sensor 01-23-32-66-C6-FE-0B-8D-EE-V Value 3.31
Interrupt Triggered: RisingEdge

Wireless field gateway protocol V1

I’m going to build a number of nRF2L01P field gateways (Netduino Ethernet & Wifi running .NetMF, Raspberry PI running Windows 10 IoT Core, RedBearLab 3200  etc.), clients which run on a variety of hardware (Arduino, devDuino, Netduino, Seeeduino etc.) which, then upload data to a selection of IoT Cloud services (AdaFruit.IO, ThingSpeak, Microsoft IoT Central etc.)

The nRF24L01P is widely supported with messages up to 32 bytes long, low power consumption and 250kbps, 1Mbps and 2Mbps data rates.

The aim is to keep the protocol simple (telemetry only initially) to implement and debug as the client side code will be utilised by high school student projects.

The first byte of the message specifies the message type

0 = Echo

The message is displayed by the field gateway as text & hexadecimal.

1 = Device identifier + Comma separated values (CSV) payload

[0] – Set to 1

[1] – Device identifier length

[2]..[2+Device identifier length] – Unique device identifier bytes e.g. Mac address

[2+Device identifier length+1 ]..[31] – CSV payload e.g.  SensorID value, SensorID value

Overtime I will support more message types and wireless protocols.


nRF24 Windows 10 IoT Core Background Task

First step is to build a basic Windows 10 IoT Core background task which can receive and display messages sent from a variety of devices across an nRF24L01 wireless link.

If you create a new “Windows IoT Core” “Background Application” project then copy this code into StartupTasks.cs the namespace has to be changed in the C# file, project properties\library\Default namespace and “Package.appxmanifest”\declarations\Entry Point.


Copyright ® 2017 December devMobile Software, All Rights Reserved



using System;
using System.Diagnostics;
using System.Text;
using Radios.RF24;
using Windows.ApplicationModel.Background;

namespace devmobile.IoTCore.nRF24BackgroundTask
    public sealed class StartupTask : IBackgroundTask
      private const byte ChipEnablePin = 25;
      private const byte ChipSelectPin = 0;
      private const byte nRF24InterruptPin = 17;
      private const string BaseStationAddress = "Base1";
      private const byte nRF24Channel = 10;
      private RF24 Radio = new RF24();
      private BackgroundTaskDeferral deferral;

      public void Run(IBackgroundTaskInstance taskInstance)
         Radio.OnDataReceived += Radio_OnDataReceived;
         Radio.OnTransmitFailed += Radio_OnTransmitFailed;
         Radio.OnTransmitSuccess += Radio_OnTransmitSuccess;

         Radio.Initialize(ChipEnablePin, ChipSelectPin, nRF24InterruptPin);
         Radio.Address = Encoding.UTF8.GetBytes(BaseStationAddress);
         Radio.Channel = nRF24Channel;
         Radio.PowerLevel = PowerLevel.High;
         Radio.DataRate = DataRate.DR250Kbps;
         Radio.IsEnabled = true;

         Debug.WriteLine("Address: " + Encoding.UTF8.GetString(Radio.Address));
         Debug.WriteLine("PA: " + Radio.PowerLevel);
         Debug.WriteLine("IsAutoAcknowledge: " + Radio.IsAutoAcknowledge);
         Debug.WriteLine("Channel: " + Radio.Channel);
         Debug.WriteLine("DataRate: " + Radio.DataRate);
         Debug.WriteLine("IsDynamicAcknowledge: " + Radio.IsDyanmicAcknowledge);
         Debug.WriteLine("IsDynamicPayload: " + Radio.IsDynamicPayload);
         Debug.WriteLine("IsEnabled: " + Radio.IsEnabled);
         Debug.WriteLine("Frequency: " + Radio.Frequency);
         Debug.WriteLine("IsInitialized: " + Radio.IsInitialized);
         Debug.WriteLine("IsPowered: " + Radio.IsPowered);

         deferral = taskInstance.GetDeferral();

         Debug.WriteLine("Run completed");

      private void Radio_OnDataReceived(byte[] data)
         // Display as Unicode
         string unicodeText = Encoding.UTF8.GetString(data);
         Debug.WriteLine("Unicode - Payload Length {0} Unicode Length {1} Unicode text {2}", data.Length, unicodeText.Length, unicodeText);

         // display as hex
         Debug.WriteLine("Hex - Length {0} Payload {1}", data.Length, BitConverter.ToString(data));

      private void Radio_OnTransmitSuccess()
         Debug.WriteLine("Transmit Succeeded!");

      private void Radio_OnTransmitFailed()
         Debug.WriteLine("Transmit Failed!");

This was displayed in the output window of Visual Studio

Address: Base1
PA: 15
IsAutoAcknowledge: True
Channel: 10
DataRate: DR250Kbps
IsDynamicAcknowledge: False
IsDynamicPayload: True
IsEnabled: True
Frequency: 2410
IsInitialized: True
IsPowered: True
Run completed

Interrupt Triggered: FallingEdge
Unicode – Payload Length 19 Unicode Length 19 Unicode text T  23.8,H  73,V 3.26
Hex – Length 19 Payload 54-20-32-33-2E-38-2C-48-20-20-37-33-2C-56-20-33-2E-32-36
Interrupt Triggered: RisingEdge

Note the odd formatting of the Temperature and humidity values which is due to the way dtostrf function in the Atmel AVR library works.

Also noticed the techfooninja nRF24 library has configurable output power level which I will try to retrofit onto the Gralin NetMF library.

Next, several simple Arduino, devDuino V2.2, Seeeduino V4.2 and Netduino 2/3 clients (plus possibly some others)

nRF24 Windows 10 IoT Core reboot

My first live deployment of the nRF24L01 Windows 10 IoT Core field gateway is now scheduled for mid Q1 2018 so time for a reboot. After digging out my Raspbery PI 2/3 devices and the nRF24L01+ shield (with modifications detailed here) I have a basic plan with some milestones.

My aim is to be able to wirelessly acquire data from several dozen Arduino, devduino, seeeduino, and Netduino devices, Then, using a field gateway on a Raspberry PI running Windows 10 IoT Core upload it to Microsoft IoT Central

First bit of code – Bleepy a simple background application to test the piezo beeper on the RPI NRF24 Shield

namespace devmobile.IoTCore.Bleepy
   public sealed class StartupTask : IBackgroundTask
      private BackgroundTaskDeferral deferral;
      private const int ledPinNumber = 4;
      private GpioPin ledGpioPin;
      private ThreadPoolTimer timer;

      public void Run(IBackgroundTaskInstance taskInstance)
         var gpioController = GpioController.GetDefault();
         if (gpioController == null)
            Debug.WriteLine("GpioController.GetDefault failed");

         ledGpioPin = gpioController.OpenPin(ledPinNumber);
         if (ledGpioPin == null)
            Debug.WriteLine("gpioController.OpenPin failed");


         this.timer = ThreadPoolTimer.CreatePeriodicTimer(Timer_Tick, TimeSpan.FromMilliseconds(500));

         deferral = taskInstance.GetDeferral();

         Debug.WriteLine("Rum completed");

      private void Timer_Tick(ThreadPoolTimer timer)
         GpioPinValue currentPinValue = ledGpioPin.Read();

         if (currentPinValue == GpioPinValue.High)

Note the blob of blu tack over the piezo beeper to mute noise

Netduino 3 Wifi Queued Azure Event Hub Field Gateway V1.0

My ADSL connection had been a bit flaky which had meant I had lost some sensor data with my initial Azure Event Hub gateway. In attempt make the solution more robust this version of the gateway queues unsent messages using the on-board MicroSD card support.

The code assumes that a file move is an “atomic operation”, so it streams the events received from the devices into a temporary directory (configurable) then moves them to the upload directory (configurable).

This code is proof of concept and needs to be soak tested, improved error handling and some additional multi threading locking added plus the magic constants refactored.

This code is called in the nRF24 receive messages handler

private void OnReceive(byte[] data)

   // Ensure that we have a payload
   if (data.Length < 1 )
      Debug.Print( "ERROR - Message has no payload" ) ;
      return ;

   string message = new String(Encoding.UTF8.GetChars(data));
   Debug.Print("+" + DateTime.UtcNow.ToString("HH:mm:ss") + " L=" + data.Length + " M=" + message);

   string filename = DateTime.UtcNow.ToString("yyyyMMddhhmmssff") + ".txt";

   string tempDirectory = Path.Combine("\\sd", "temp");
   string tempFilePath = Path.Combine(tempDirectory, filename);

   string queueDirectory = Path.Combine("\\sd", "data");
   string queueFilePath = Path.Combine(queueDirectory, filename);

   File.WriteAllBytes(tempFilePath, data);

   File.Move(tempFilePath, queueFilePath);

   new Microsoft.SPOT.IO.VolumeInfo("\\sd").FlushAll();

A timer initiates the upload process which uses the AMQPNetlite library

bool UploadInProgress = false;

void uploaderCallback(object state)
   Debug.Print("uploaderCallback - start");

   if (UploadInProgress)
   UploadInProgress = true;

   string[] eventFilesToSend = Directory.GetFiles(Path.Combine("\\sd", "data")) ;

   if ( eventFilesToSend.Length == 0 )
      Debug.Print("uploaderCallback - no files");
      UploadInProgress = false;
      return ;

      Debug.Print("uploaderCallback - Connect");
      Connection connection = new Connection(new Address(serviceBusHost, serviceBusPort, serviceBusSasKeyName, serviceBusSasKey));

      Session session = new Session(connection);

      SenderLink sender = new SenderLink(session, "send-link", eventHubName);

      for (int index = 0; index < System.Math.Min(eventUploadBatchSizeMaximum, eventFilesToSend.Length); index++)
         string eventFile = eventFilesToSend[ index ] ;

         Debug.Print("-" + DateTime.UtcNow.ToString("HH:mm:ss") + " " + eventFile ); ;

         Message message = new Message()
            BodySection = new Data()
               Binary = File.ReadAllBytes(eventFile),
         ApplicationProperties = new Amqp.Framing.ApplicationProperties(),

         FileInfo fileInfo = new FileInfo(eventFile);

         message.ApplicationProperties["AcquiredAtUtc"] = fileInfo.CreationTimeUtc;
         message.ApplicationProperties["UploadedAtUtc"] = DateTime.UtcNow;
         message.ApplicationProperties["GatewayId"] = gatewayId;
         message.ApplicationProperties["DeviceId"] = deviceId;
         message.ApplicationProperties["EventId"] = Guid.NewGuid();



         new Microsoft.SPOT.IO.VolumeInfo("\\sd").FlushAll();

   catch (Exception ex)
      Debug.Print("ERROR: Upload failed with error: " + ex.Message);
      Debug.Print("uploaderCallback - finally");
      UploadInProgress = false;

The timer period and number of files uploaded in each batch is configurable. I need to test the application to see how it handles power outages and MicroSD card corruption. The source is Netduino NRF24L01 AMQPNetLite Queued Azure EventHub Gatewaywith all the usual caveats.

This project wouldn’t have been possible without

MS Ignite Auckland NZ Presentation now available online

My presentation “All your device are belong to us” [M240] is now online at MSDN Channel 9

So much hype, so many different devices, so many protocols, so much data, so little security, welcome to the Internet of Things. Come and see how you can build an affordable, securable, scalable, interoperable, robust & reliable solution with embedded devices, Windows 10 IoT and Microsoft Azure. By 2020 there will be 26 Billion devices and 4.5 million developers building solutions so the scope is limitless.

I had 8 devices in my presentation so the scope for disaster was high.

The first demo was of how sensors could be connected across Arduino, Netduino and Raspberry PI platforms.

The Arduino demo used

The Netduino demo used

The Raspbery PI Windows 10 IoT Core demo used

The hobbyist data acquisition demo collected data from two devduino devices that were in passed around by the audience and were each equipped with a Temperature & Humidity sensor. They uploaded data to Xively over an NRF24L01 link to a gateway running on a Netduino 3 Ethernet and the data was displayed in real-time on my house information page

The professional data acquisition demo uploaded telemetry data to an Azure ServiceBus EventHub and retrieved commands from an Azure ServiceBus Queue. Both devices were running software based on Azure ServiceBus Lite by Paolo Paiterno

The telemetry stream was the temperature of some iced water.

The commands were processed by a Raspbery PI running Windows 10 IoT Core which turned a small fan on & off to illustrate how a FrostFan could be used in a vineyard to reduce frost damage to the vines.

Frost Fan demo

MS Ignite 2015 Frost Fan demo

My demos all worked on the day which was a major win as many other presenters struggled with connectivity. Thanks to the conference infrastructure support guys who helped me sort things out.

With the benefit of hindsight, I tried to fit too much in and the overnight partial rewrite post attending the presentation Mashup the Internet of Things, Azure App Service and Windows 10 to Deliver Business Value [M387] by Rob Tiffany was a bit rushed.