Spent several hours last night ordering all the bits for the next month’s code club sessions. Can take a couple of weeks for parts to arrive from China and the USA so I have to plan well in advance.
We now have 16 Netduino’s plus enough kit for
The groups of students will get to build each project over a couple of nights.
A couple of weeks ago I ordered a Joystick Shield V2.4 from elecfreaks and it arrived yesterday. This shield with baked in nRF24L01 support looked quite promising as the basis for a handheld remote control for a robot or quadcopter. The shield also has a Nokia 5100 display connector but I’m not planning on using that.
The other end of the remote control link will be based on an embedded coolness nRF24L01 shield which I have looked at in a previous post. The robot radio link would use a pair of short range nRF24L01 modules and the quadcopter would use long range nRF24L01 modules.
When I checked the wiring diagram for the shield, the interrupt pin of the nRF24L01 socket was not connected to anything. The Nordic nRF24L01 .Net Micro Framework Driver on Codeplex (used for the both ends of the link) is interrupt driven so a small modification to the shield was required. I connected the interrupt pin (pin 8) of the nRF24L01 socket to DIO Pin1
The sample application from the previous post requires a small change to the initialisation code to work with the Joystick shield.
public void Run()
{
_module.OnDataReceived += OnReceive;
_module.OnTransmitFailed += OnSendFailure;
_module.OnTransmitSuccess += OnSendSuccess;
_module.Initialize(SPI.SPI_module.SPI1, Pins.GPIO_PIN_D10, Pins.GPIO_PIN_D9, Pins.GPIO_PIN_D1);
All of the buttons (A to F & Joystick push) are connected to digital inputs and the input voltage (3.3V or 5V) for the joystick x & y is selected using a switch which is perfect for my Netduino based project
Bill of materials (prices as at Jan 2014)
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
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 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
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.
A fortnight ago I purchased two shields from Embedded Coolness for a couple of nRF24L01 based projects (quadcopter & robot control system) I’m working on.The shields were very reasonably priced and took roughly 10-15 minutes each to assemble.
nRF24L01 Shield with short range module
Though intended for Arduino based projects the hardware SPI port works with the Nordic nRF24L01 .Net Micro Framework Driver on Codeplex.
I adapted the sample application included with the Nordic nRF24L01 .Net Micro Framework Driver source from codeplex to give a minimal working Netduino example.
...
public class EmbeddCoolnessTestHarness
{
private const byte channel = 10;
private readonly OutputPort _led = new OutputPort(Pins.ONBOARD_LED, false);
private readonly NRF24L01Plus _module;
private Timer _timer;
private byte _token;
private readonly byte[] _myAddress = Encoding.UTF8.GetBytes("NetP1");
private readonly byte[] _otherBoard = Encoding.UTF8.GetBytes("NetP2");
public EmbeddCoolnessTestHarness()
{
_module = new NRF24L01Plus();
}
public void Run()
{
_module.OnDataReceived += OnReceive;
_module.OnTransmitFailed += OnSendFailure;
_module.OnTransmitSuccess += OnSendSuccess;
// we need to call Initialize() and Configure() before we start using the module
_module.Initialize(SPI.SPI_module.SPI1, Pins.GPIO_PIN_D7, Pins.GPIO_PIN_D3, Pins.GPIO_PIN_D2);
_module.Configure(_myAddress, channel);
_module.Enable();
_timer = new Timer(SendMessage, null, new TimeSpan(0, 0, 0, 1), new TimeSpan(0, 0, 0, 1));}
private void OnSendSuccess()
{
_led.Write(false);
}
private void OnSendFailure()
{
Debug.Print("Send failed!");
}
private void OnReceive(byte[] data)
{
Debug.Print("Token = " + data[0]);
}
private void SendMessage(object state)
{
_led.Write(true);
_module.SendTo(_otherBoard, new[] { _token });
_token++;
}
}
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”.
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 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)
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 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 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.
In the final couple of code club sessions we built a pulse rate monitor to illustrate a practical application for the NetMF InterruptPort, and communication between threads using Interlocked (Increment & exchange). The V1 application displays the approximate pulse rate in Beats Per Minute (BPM) using Debug.Print.
The SeeedStudio Grove Ear clip heart rate sensor strobes a digital input for each heart beat it detects and this is used to trigger an interrupt handler. In the interrupt handler we incremented a counter using Interlocked.Increment.
A timer fires every 15 seconds which takes a copy of the current count, resets it to zero using Interlocked.Exchange. This code then multiplies the count by the number of times the timer fires per minute to convert it to BPM for display.
We discussed different approaches for determining the pulse rate and for V1 a 15 second timer seemed to be a reasonable trade off between accuracy and reading update latency.
Pulserate monitor
public class Program
{
const int mSecPerMinute = 60000;
const int displayUpdateRatemSec = 15000;
private static InterruptPort heartBeatSensor = new InterruptPort(Pins.GPIO_PIN_D1, false, Port.ResistorMode.Disabled, Port.InterruptMode.InterruptEdgeHigh);
private static OutputPort heartBeatDisplayLed = new OutputPort(Pins.GPIO_PIN_D6, false);
private static int heartBeatCount = 0;</code>
public static void Main()
{
heartBeatSensor.OnInterrupt += pulse_OnInterrupt;
Timer pulseRateDisplayTimer = new Timer(PulseRateDisplayTimerCallback, null, displayUpdateRatemSec, displayUpdateRatemSec);
Thread.Sleep(Timeout.Infinite);
}
static void pulse_OnInterrupt(uint data1, uint data2, DateTime time)
{
heartBeatDisplayLed.Write(!heartBeatDisplayLed.Read());
Interlocked.Increment(ref heartBeatCount);
}
static void PulseRateDisplayTimerCallback(object state)
{
int displayPulseCount ;</code>
displayPulseCount = Interlocked.Exchange(ref heartBeatCount, 0 );
displayPulseCount = displayPulseCount * (mSecPerMinute / displayUpdateRatemSec);
Debug.Print("Pulse rate " + displayPulseCount + " bpm");
}
}
Bill of materials (Prices as at Dec 2013)
A few weeks ago my 6 year old son took his Nerf SuperSoaker to the beach and the salt water damaged the battery pack. Yesterday he pulled it apart to see how it worked and after a couple of quick tests with the multimeter we worked out the switch on the battery pack was the problem.
While it was dismantled we decided to “enhance” it with a Netduino+ and an ultrasonic range finder so it squirted water automatically when a target got with 2.5m. The code for the Ultrasonic range finder was adapted from Dave’s code on Netduino.com
Bill of Materials
A chat with some co-workers about displaying the status of the team’s Jenkins build process led to bit of research into calling RESTful services and JSON support on NetMF devices. Previously this had required a bit of hand crafted code but now it looks like the library support has matured a bit. I don’t run Jenkins at home so I decided to build a NetduinoPlus client for the internet Chuck Norris database which has a RESTful API.
This API returns Chuck Norris “facts”…
“Chuck Norris doesn’t read books. He stares them down until he gets the information he wants.”
“There is no theory of evolution, just a list of creatures Chuck Norris allows to live.”
“Some people wear Superman pajamas. Superman wears Chuck Norris pajamas.”
“Chuck Norris can slam a revolving door.”
The icndb API returns JSON
{ "type": "success", "value": { "id": 109, "joke": "It takes Chuck Norris 20 minutes to watch 60 Minutes.", "categories": [] } }
I used the NetMF system.HTTP libraries to initiate the request and Json.NetMF to unpack the response. This snippet illustrates how I processed the request/response
using (HttpWebRequest request = (HttpWebRequest)WebRequest.Create(@"http://api.icndb.com/jokes/random"))
{
//request.Proxy = proxy;
request.Method = "GET";
request.KeepAlive = false;
request.Timeout = 5000;
request.ReadWriteTimeout = 5000;
using (var response = (HttpWebResponse)request.GetResponse())
{
if (response.StatusCode == HttpStatusCode.OK)
{
byte[] buffer = new byte[response.ContentLength];
using (Stream stream = response.GetResponseStream())
{
stream.Read(buffer, 0, (int)response.ContentLength);
string json = new string(Encoding.UTF8.GetChars(buffer));
Hashtable jsonPayload = JsonSerializer.DeserializeString(json) as Hashtable;
Hashtable value = jsonPayload["value"] as Hashtable ;
Debug.Print(value["joke"].ToString());
}
}
}
}
Bill of materials
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