EVolocity 3 Axis G-Meter

A telemetry system could be used to monitor the progress of your electric vehicle and provide feedback to the team & driver about how efficiently/fast it is being driven. As part of a telemetry system lateral, longitudinal, and vertical acceleration could be monitored using a cheap ADXL345 mems accelerometer

Netduino based 3D GMeter

Netduino based 3D G-Meter

Bill of Materials for my engineering proof of concept (Prices as at May 2015)

The sample code reads the acceleration data from the ADXL345 using a driver originally created by Love Electronics. It then displays the magnitude of the scaled acceleration on 3 x LED Bars using code written by Famoury Toure

OutputPort Xcin = new OutputPort(Pins.GPIO_PIN_D0, false);
OutputPort Xdin = new OutputPort(Pins.GPIO_PIN_D1, false);
OutputPort Ycin = new OutputPort(Pins.GPIO_PIN_D3, false);
OutputPort Ydin = new OutputPort(Pins.GPIO_PIN_D4, false);
OutputPort Zcin = new OutputPort(Pins.GPIO_PIN_D5, false);
OutputPort Zdin = new OutputPort(Pins.GPIO_PIN_D6, false);

GroveLedBarGraph Xbar = new GroveLedBarGraph(Xcin, Xdin);
GroveLedBarGraph Ybar = new GroveLedBarGraph(Ycin, Ydin);
GroveLedBarGraph Zbar = new GroveLedBarGraph(Zcin, Zdin);

using (OutputPort i2cPort = new OutputPort(Pins.GPIO_PIN_SDA, true))

ADXL345 accel = new ADXL345(0x53);
accel.Range = 2;
accel.FullResolution = true;

while (true)

   uint xValue = (uint)(((accel.ScaledXAxisG / 1.0 ) + 1.0) * 5.0) ;
   uint xbar = 1;
   xbar = xbar << (int)xValue;

   uint yValue = (uint)(((accel.ScaledYAxisG / 1.0) + 1.0) * 5.0);
   uint ybar = 1;
   ybar = ybar << (int)yValue;

   uint zValue = (uint)((-(accel.ScaledZAxisG / 1.0) + 2.0) * 5.0);
   uint zbar = 1;
   zbar = zbar << (int)zValue;


St Margaret’s CodeClub information

If you want to follow along at home all the software is free (Visual Studio Express 2013) or open source (Netduino software & Hardware + NetMF) and can be downloaded from the following locations. The packages need to be sequentially installed in the order below.

If you want to purchase your own hardware, we use Netduino 2 Plus devices (we use them mainly for their integrated networking and MicroSD card) and Seeedstudio Grove sensors. (Prices as at 05/2015)

We are looking into Apple friendly options for later this term.

Netduino 3 wifi Azure Event Hub client

Over the last couple of weeks I have been beta testing a Netduino 3 Wifi board. One of the great features of the new board is baked in support for SSL 3.0 and TLS 1.2 which enables direct connection to services which require https.

EDIT: The device has been running under my desk powered by a wall wart for a week. It has been monitoring the temperature of my office and the air gap between the curtains and the glass. My ADSL has gone down a couple of times but the N3 has recovered all by itself and kept on going.

In a couple of previous blog posts I have shown how to upload data to an Azure Event Hub from other NetMFdevices. I built an application that runs on a FEZ Spider and a lightweight Service Gateway so I was keen to see how well a Netduino 3 Wifi based solution worked.

To get something working on my Netduino 3 device I started with the application I had written for the FEZ spider. The code is based on OBD Recorder for .Net Micro Framework with ServiceBus, AMQP (for IoT) samples. The test client used a couple of DS18B20 temperature sensors to monitor the temperature of my fridge and freezer.

Netduino 3 device with temperature sensors

Netduino 3 device with Seeedstudio Shield and two temperature sensors

I created an Event Hub and associated device access keys and fired up Service Bus Explorer so I could see what was happening.ServiceBus Explorer showing my fridge and freezer temperatures

In the application the first step was to add code to wait for the device to acquire an IP address. (Will replace this code with a more efficient approach)

// Wait for Network address if DHCP
NetworkInterface networkInterface = NetworkInterface.GetAllNetworkInterfaces()[0];

if (networkInterface.IsDhcpEnabled)
   Debug.Print(" Waiting for IP address " );

   while (NetworkInterface.GetAllNetworkInterfaces()[0].IPAddress == IPAddress.Any.ToString()) ;

// Display network config for debugging
Debug.Print("Network configuration");
Debug.Print(" Gateway: " + networkInterface.GatewayAddress.ToString());

foreach (string dnsAddress in networkInterface.DnsAddresses)

deviceId = BytesToHexString(networkInterface.PhysicalAddress);

Then to send the message to the event hub the request has to have a authorisation token attached

private void EventHubSendMessage(string eventHubAddressHttps, string messageBody)
   string token = CreateSasToken(eventHubAddressHttps + "/messages", sasKeyName, sasKeyText);

      using( HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(eventHubAddressHttps + "/messages" + "?timeout=60" + ApiVersion))
         request.Timeout = 2500;
         request.Method = "POST";

         // Enable these options to suit your environment
         //request.Proxy = new WebProxy("myproxy.myorganisation.com", true);
         //request.Credentials = new NetworkCredential("myusername", "mytopsecretpassword"); 

         request.Headers.Add("Authorization", token);
         request.Headers.Add("ContentType", "application/json;charset=utf-8");

         byte[] buffer = Encoding.UTF8.GetBytes(messageBody);

         request.ContentLength = buffer.Length;

         // request body
         using (Stream stream = request.GetRequestStream())
            stream.Write(buffer, 0, buffer.Length);

         using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
   catch (WebException we)

// Create a SAS token for a specified scope. SAS tokens are described in http://msdn.microsoft.com/en-us/library/windowsazure/dn170477.aspx.
private static string CreateSasToken(string uri, string keyName, string key)
   // Set token lifetime to 20 minutes. When supplying a device with a token, you might want to use a longer expiration time.
   uint tokenExpirationTime = GetExpiry(20 * 60);

   string stringToSign = HttpUtility.UrlEncode(uri) + "\n" + tokenExpirationTime;

   var hmac = SHA.computeHMAC_SHA256(Encoding.UTF8.GetBytes(key), Encoding.UTF8.GetBytes(stringToSign));
   string signature = Convert.ToBase64String(hmac);

   signature = Base64NetMf42ToRfc4648(signature);

   string token = "SharedAccessSignature sr=" + HttpUtility.UrlEncode(uri) + "&sig=" + HttpUtility.UrlEncode(signature) + "&se=" + tokenExpirationTime.ToString() + "&skn=" + keyName;

   return token;

private static string Base64NetMf42ToRfc4648(string base64netMf)
   var base64Rfc = string.Empty;

   for (var i = 0; i < base64netMf.Length; i++)
      if (base64netMf[i] == '!')
         base64Rfc += '+';
      else if (base64netMf[i] == '*')
         base64Rfc += '/';
         base64Rfc += base64netMf[i];
   return base64Rfc;

static uint GetExpiry(uint tokenLifetimeInSeconds)
   const long ticksPerSecond = 1000000000 / 100; // 1 tick = 100 nano seconds

   TimeSpan diff = DateTime.Now.ToUniversalTime() - origin;

   return ((uint)(diff.Ticks / ticksPerSecond)) + tokenLifetimeInSeconds;

The initial version of the Netduino TI CC3100 driver has some limitations e.g. no server certificate validation but these should be attended to in future releases.

The software was based on Brad’s One-Wire and DS18B20 library with fixes from here.