Xively GPS Location data upload V2

In the previous post I assembled the xively request XML using a StringBuilder rather than using the XML support available in the NetMF. To use the NetMF XML library I needed to add a reference to the DPWS extensions (MFDpwsExtensions) and change the using statement at the top of the module from System.Text to System.Ext.Xml

static void xivelyFeedUpdate(string ApiKey, string feedId, string channel, double latitude, double longitude, double altitude)
{
byte[] buffer;

using (XmlMemoryWriter xmlwriter = XmlMemoryWriter.Create())
{
xmlwriter.WriteProcessingInstruction("xml", "version=\"1.0\" encoding=\"utf-8\"");
xmlwriter.WriteStartElement("eeml");
xmlwriter.WriteStartElement("environment");
xmlwriter.WriteStartElement("location");

xmlwriter.WriteStartAttribute("domain");
xmlwriter.WriteString("physical");
xmlwriter.WriteEndAttribute();

xmlwriter.WriteStartAttribute("exposure");
xmlwriter.WriteString("outdoor");
xmlwriter.WriteEndAttribute();

xmlwriter.WriteStartAttribute("disposition");
xmlwriter.WriteString("mobile");
xmlwriter.WriteEndAttribute();

xmlwriter.WriteStartElement("name");
xmlwriter.WriteString("Location");
xmlwriter.WriteEndElement();

xmlwriter.WriteStartElement("lat");
xmlwriter.WriteString(latitude.ToString("F5"));
xmlwriter.WriteEndElement();

xmlwriter.WriteStartElement("lon");
xmlwriter.WriteString(longitude.ToString("F5"));
xmlwriter.WriteEndElement();

xmlwriter.WriteStartElement("ele");
xmlwriter.WriteString(altitude.ToString("F1"));
xmlwriter.WriteEndElement();

xmlwriter.WriteEndElement();
xmlwriter.WriteEndElement();
xmlwriter.WriteEndElement();

buffer = xmlwriter.ToArray();
}

try
{
using (HttpWebRequest request = (HttpWebRequest)WebRequest.Create(xivelyApiBaseUrl + feedId + ".xml"))
{
request.Method = "PUT";
request.ContentLength = buffer.Length;
request.ContentType = "text/xml";
request.Headers.Add("X-ApiKey", xivelyApiKey);
request.KeepAlive = false;
request.Timeout = 5000;
request.ReadWriteTimeout = 5000;

// request body
using (Stream stream = request.GetRequestStream())
{
stream.Write(buffer, 0, buffer.Length);                }
using (var response = (HttpWebResponse)request.GetResponse())
{
Debug.Print("HTTP Status:" + response.StatusCode + " : " + response.StatusDescription);
}
}
}
catch (Exception ex)
{
Debug.Print(ex.Message);
}
}

I was expecting the XML libraries to be quite chunky, but on my Netduino Plus 2 there wasn’t a huge size difference, the StringBuilder download was 49K8 bytes and the XMLWiter download was 56K1 bytes.

When I ran the StringBuilder and XMLWriter versions they both had roughly 92K6 bytes of free memory.

Realistically there was little to separate the two implementations

Xively GPS Location data upload V1

For one of the code club projects we looked at the National Marine Electronics Association (NMEA) 0183 output of my iteadStudio GPS Shield + Active Antenna. We used the NetMF Toolbox NMEA GPS processing code with a couple of modifications detailed here.

IteadStudio GPS

IteadStudio GPS shield and Antenna

For another project we had used Xively a “Public Cloud for the Internet of Things”. The Xively API has support for storing the position of a “thing” and it didn’t look like it would take much effort to extend the original GPS demo to trial this. The xively Location & waypoints API is RESTful and supports JSON & XML

void xivelyFeedUpdate(string ApiKey, string feedId, string channel, double latitude, double longitude, double altitude)
{
try
{
using (HttpWebRequest request = (HttpWebRequest)WebRequest.Create(xivelyApiBaseUrl + feedId + ".xml"))
{
StringBuilder payload = new StringBuilder();
payload.Append(@"<?xml version=""1.0"" encoding=""UTF-8""?><eeml><environment><location domain=""physical"" exposure=""outdoor"" disposition=""mobile""><name>Location</name><lat>");
payload.Append(latitude.ToString("F5"));
payload.Append("</lat><lon>");
payload.Append(longitude.ToString("F5"));
payload.Append("</lon><ele>");
payload.Append(altitude.ToString("F1"));
payload.Append("</ele></location></environment></eeml>");

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

request.Method = "PUT";
request.ContentLength = buffer.Length;
request.ContentType = "text/xml";
request.Headers.Add("X-ApiKey", xivelyApiKey);
request.KeepAlive = false;
request.Timeout = 5000;
request.ReadWriteTimeout = 5000;

// request body
using (Stream stream = request.GetRequestStream())
{
stream.Write(buffer, 0, buffer.Length);
}
using (var response = (HttpWebResponse)request.GetResponse())
{
Debug.Print("HTTP Status:" + response.StatusCode + " : " + response.StatusDescription);
}
}
}
catch (Exception ex)
{
Debug.Print(ex.Message);
}
}

The position of the “thing” is displayed like this

Xively poisition

The position of my car

The XML was constructed using a stringbuilder (NetMF 4.2) as this appeared easier/smaller than using the baked in XML functionality.

Netduino Plus PulseRate Monitor V2

In the final couple of code club sessions we built a pulse rate monitor to show a practical application for the NetMF InterruptPort, and communication between threads using the Interlocked class (Increment & exchange). This was then enhanced to display the data locally and upload it to the cloud to illustrate a basic HTTP interaction and serial communications.

The application displays the approximate pulse rate in Beats Per Minute (BPM) on a 16×2 character LCD display and also uploads the information to a free developer account at Xively a “Public Cloud for the Internet of Things”.

Netduino Plus 2 rate monitor

The xively trial account has a limit of 25 calls a minute, rolling 3 minute average (Dec 2013) which was more than adequate for our application and many other educational projects.

The xively API supports managing products, managing devices,  reading & writing data, reading & wiring metadata, querying historical data and searching for data feeds, using a RESTful approach.

The NetduinoPlus2 has full support for the NetMF system.http and sufficient memory so that there is plenty of room left for an application. If you are using a Netduino Plus (or other NetMF device with limited memory) an approach which reduces memory consumption is detailed here.

The xively data API supports JSON, XML and CSV formats for upload of data and for the pulse rate monitor we used CSV. The following code was called roughly every 20 seconds.

static void xivelyFeedUpdate( string ApiKey, string feedId, string channel, string value )
{
try
{
using (HttpWebRequest request = (HttpWebRequest)WebRequest.Create(xivelyApiBaseUrl+ feedId + ".csv"))
{
byte[] buffer = Encoding.UTF8.GetBytes(channel + "," + value);


request.Method = "PUT";
request.ContentLength = buffer.Length;
request.ContentType = "text/csv";
request.Headers.Add("X-ApiKey", ApiKey);
request.KeepAlive = false;
request.Timeout = 5000;
request.ReadWriteTimeout = 5000;


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


using (var response = (HttpWebResponse)request.GetResponse())
{
Debug.Print("HTTP Status:" + response.StatusCode + " : " + response.StatusDescription);
}
}
}
catch (Exception ex)
{
Debug.Print(ex.Message);
}
}

The pulse rate information can then displayed by xively in tables and graphs.

Pulse Rate data gaph at xively

Pulse Rate data display

At the end of term presentation several parents and family members were doing press-ups and other exercises to see how high their pulse rate went and how quickly it recovered.

Bill of materials (Prices as at Dec 2013)

SeeedStudio Grove GPS IteadStudio Shield Comparison

I use the SeeedStudio Grove system for prototyping and teaching. One of the modules is a Global Positioning System (GPS) unit based on the u-blox 5 engine. To get this unit to work you just plug it into the UART socket on the base shield and load the necessary software onto an Arduino (or compatible) board. My day job is working on Microsoft .Net applications so I use a Netduino Plus or a Netduino plus 2.

SeeedStudio GPS unit

SeeedStudio base shield and GPS unit

The Seeedstudio 4 wire connector system has some advantages but for a couple of projects I was looking at I needed to be able to run on a different serial port and access the one pulse per second output. I had a look at several other vendors and the iteadstudio GPS Shield + Active Antenna which is based on the u-blox 6 engine looked like a reasonable alternative.

IteadStudio GPS

IteadStudio GPS shield and Antenna

After some testing I found that the Iteadstudio GPS shield appears to have a shorter time to first fix after a power cycle, I averaged 10 sets of readings for each device and found that in my backyard it took on average 46sec for the Iteadstudio shield and 55sec for the SeeedStudio device.

Both devices output National Marine Electronics Association (NMEA) 0183 sentences and I use the NetMF Toolbox NMEA code to process the data streams. I have modified the NetMF toolbox code with an additional event handler which empties the serial input buffer if there is an error and one of the validation checks needed to be tweaked as it was possible to get an exception due to an empty string.

Around line 45

this._Uart = newSerialPort(SerialPort, BaudRate);
this._Uart.ErrorReceived += newSerialErrorReceivedEventHandler(_Uart_ErrorReceived);
this._Uart.DataReceived += newSerialDataReceivedEventHandler(_Uart_DataReceived);


void _Uart_ErrorReceived(object sender, SerialErrorReceivedEventArgs e)
{
if (_Uart.IsOpen)
{
_Uart.Flush();
}
}

Around line 323

// Have we received a full line of data?
int Pos = this._Buffer.IndexOf("\r\n");
if (Pos >= 1)
{

With these modifications my Netduino Plus 2 can runs for days at a time without buffer overflows or other issues, you just need to be careful to make your event handlers block for as little time as possible.

I have been looking at building an NetMF NMEA driver which runs on a background thread and doesn’t use any string manipulation methods e.g. string.splt so the garbage collector has less to do, but this will be a topic for a future post.