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Building Your Own Video Game Controller

Parts Needed:
1 BASIC Stamp HomeWork Board
1 Memsic 2125 Dual-Axis Accelerometer

Playing video games is always a great way to have some fun. Designing your own video games adds a little more to the enjoyment. But, what's next? How about building your own game controllers and interfaces? I believe that how we interact with video games has taken several leaps forward lately with the addition of the Wii-mote controller, the PlayStation3 with tilt and motion, and the extensions of guitars and drums from Guitar Hero and Rock Band.

In this tutorial, I will explain how to create your own video game controller / interface with tilt using a 2-axis accelerometer and a BasicStamp2.

To get started, we need to gather the necessary parts. First, we need a basic development board. For this tutorial, I would recommend visiting Parallax.com or the local Radio Shack and snatching one of the "What's a Microcontroller?" kits. It includes a development board with a BS2 stamp already plugged in. It also includes other parts such as LEDs, resistors, capacitors, push buttons, piezo speaker, and even a servo. It's definitely worth buying, especially if you've never done any kind of microcontroller design or development. It even comes with a very good book that explains what each part is and how to use it. You can order the kit online at Parallax's website (http://www.parallax.com or directly at http://www.parallax.com/Store/Microcontrollers/BASICStampProgrammingKits/tabid/136/CategoryID/11/List/0/SortField/0/Level/a/ProductID/327/Default.aspx).


Part #: 28152

The most important part of this kit is the development board. This version is called the HomeWork Board. It is a pre-built board that includes a solderless bread board, BS2 stamp, RS-232, etc... This is a great board for quick and easy development.

HomeWork Board

Part #: 28158

http://www.parallax.com/Store/Microcontrollers/BASICStampDevelopmentBoards/tabid/137/CategoryID/12/List/0/SortField/0/Level/a/ProductID/133/Default.aspx

I chose to go with the Parallax HomeWork board because it's a very simple design and it is powered by an attached 9V battery. Most of the other boards are powered with a detached power supply. For our controller, we want our board to be very mobile and don't want a lot of extra cables dangling from it.

Note: In a future tuturial, I will show you how to make your controller wireless.


The next part we'll need for our controller is the accelerometer. So, what is an accelerometer anyways? An accelerometer is a device that measures non-gravitational accelerations. Single- and multi-axis models are verticle to detect magnitude and direction of an accleration as a vector quantity, and can be used to sense orientation, vibration, and shocks.

Accelerometers are present in numerous portable electronics and video game controllers, including the Nokia N95, Sony Ericsson W910i, Blackberry Storm, iPhone, iPod Nano 4G, Nintendo's Wii Remote, and the PlayStation3 controller. Our controller will be using the Memsic 2125 Dual-axis accelerometer from Parallax (http://www.parallax.com). It's a tilt sensor with a tiny bubble of hot air, like a carpenter's level on two axes.


Part #: 28017

http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/Level/a/ProductID/93/Default.aspx?SortField=ProductName%2cProductName

We could've used an acclerometer with more axis, but this one will do fine for our project. All we need it to do is to measure if the controller is leaning backwards, forwards, or tilting left or right.






Basic Stamp 2 Source Code
' ========================================================================= ' ' File...... MEMSIC2125-Dual.BS2 ' Purpose... Memsic 2125 Accelerometer Dual-Axis Demo ' Author.... (C) 2003-2004 Parallax, Inc -- All Rights Reserved ' E-mail.... support@parallax.com ' Started... ' Updated... 07 SEP 2004 ' ' {$STAMP BS2} ' {$PBASIC 2.5} ' ' ========================================================================= ' -----[ Program Description ]--------------------------------------------- ' ' Read the pulse outputs from a Memsic 2125 accelerometer and converts to ' G-force and tilt angle. ' ' g = ((t1 / 10 ms) - 0.5) / 12.5% ' ' Tilt = ARCSIN(g) ' ' Refer to Memsic documentation (AN-00MX-007.PDF) for details on g-to-tilt ' conversion and considerations. ' ' www.memsic.com ' -----[ Revision History ]------------------------------------------------ ' -----[ I/O Definitions ]------------------------------------------------- Xin PIN 8 ' X input from Memsic 2125 Yin PIN 9 ' Y input from Memsic 2125 ' -----[ Constants ]------------------------------------------------------- ' Set scale factor for PULSIN #SELECT $STAMP #CASE BS2, BS2E Scale CON $200 ' 2.0 us per unit #CASE BS2SX Scale CON $0CC ' 0.8 us per unit #CASE BS2P Scale CON $0C0 ' 0.75 us per unit #CASE BS2PE Scale CON $1E1 ' 1.88 us per unit #ENDSELECT HiPulse CON 1 ' measure high-going pulse LoPulse CON 0 DegSym CON 176 ' degrees symbol ' -----[ Variables ]------------------------------------------------------- xRaw VAR Word ' pulse from Memsic 2125 xmG VAR Word ' g force (1000ths) xTilt VAR Word ' tilt angle yRaw VAR Word ymG VAR Word yTilt VAR Word disp VAR Byte ' displacement (0.0 - 0.99) angle VAR Byte ' tilt angle ' -----[ EEPROM Data ]----------------------------------------------------- ' -----[ Initialization ]-------------------------------------------------- Setup: PAUSE 250 ' let DEBUG window open 'DEBUG "Memsic 2125 Accelerometer", CR, ' "-------------------------" ' -----[ Program Code ]---------------------------------------------------- Main: DO GOSUB Read_Tilt ' reads G-force and Tilt ' display results DEBUG CRSRXY, 0, 3 'DEBUG "X Input... ", ' DEC (xRaw / 1000), ".", DEC3 xRaw, " ms", ' CLREOL, CR, ' "G Force... ", (xmG.BIT15 * 13 + " "), ' DEC (ABS xmG / 1000), ".", DEC3 (ABS xmG), " g", ' CLREOL, CR, ' "X Tilt.... ", (xTilt.BIT15 * 13 + " "), ' DEC ABS xTilt, DegSym, CLREOL DEBUG (xTilt.BIT15 * 13 + " "), DEC ABS xTilt, ",", CLREOL 'DEBUG CRSRXY, 0, 7 'DEBUG "Y Input... ", ' DEC (yRaw / 1000), ".", DEC3 yRaw, " ms", ' CLREOL, CR, ' "G Force... ", (ymG.BIT15 * 13 + " "), ' DEC (ABS ymG / 1000), ".", DEC3 (ABS ymG), " g", ' CLREOL, CR, ' "Y Tilt.... ", (yTilt.BIT15 * 13 + " "), ' DEC ABS yTilt, DegSym, CLREOL DEBUG (yTilt.BIT15 * 13 + " "), DEC ABS yTilt, CLREOL PAUSE 200 ' update about 5x/second LOOP END ' -----[ Subroutines ]----------------------------------------------------- Read_G_Force: PULSIN Xin, HiPulse, xRaw ' read pulse output xRaw = xRaw */ Scale ' convert to uSecs xmG = ((xRaw / 10) - 500) * 8 ' calc 1/1000 g PULSIN Yin, HiPulse, yRaw yRaw = yRaw */ Scale ymG = ((yRaw / 10) - 500) * 8 RETURN Read_Tilt: GOSUB Read_G_Force disp = ABS xmG / 10 MAX 99 ' x displacement GOSUB Arcsine xTilt = angle * (-2 * xmG.BIT15 + 1) ' fix sign disp = ABS ymG / 10 MAX 99 ' y displacement GOSUB Arcsine yTilt = angle * (-2 * ymG.BIT15 + 1) ' fix sign RETURN ' Trig routines courtesy Tracy Allen, PhD. (www.emesystems.com) Arccosine: disp = disp */ 983 / 3 ' normalize input to 127 angle = 63 - (disp / 2) ' approximate angle DO ' find angle IF (COS angle <= disp) THEN EXIT angle = angle + 1 LOOP angle = angle */ 360 ' convert brads to degrees RETURN Arcsine: GOSUB Arccosine angle = 90 - angle RETURN

C# Source Code
Comm.cs
using System; using System.Text; using System.IO.Ports; namespace RoboWars { class Comm { #region Manager Enums /// <summary> /// enumeration to hold our transmission types /// </summary> public enum TransmissionType { Text, Hex } /// <summary> /// enumeration to hold our message types /// </summary> public enum MessageType { Incoming, Outgoing, Normal, Warning, Error }; #endregion #region Manager Variables //property variables private string _baudRate = string.Empty; private string _parity = string.Empty; private string _stopBits = string.Empty; private string _dataBits = string.Empty; private string _portName = string.Empty; private TransmissionType _transType; public float xVal = 0.0f; public float yVal = 0.0f; //global manager variables private SerialPort comPort = new SerialPort(); #endregion #region Manager Properties /// <summary> /// Property to hold the BaudRate /// of our manager class /// </summary> public string BaudRate { get { return _baudRate; } set { _baudRate = value; } } /// <summary> /// property to hold the Parity /// of our manager class /// </summary> public string Parity { get { return _parity; } set { _parity = value; } } /// <summary> /// property to hold the StopBits /// of our manager class /// </summary> public string StopBits { get { return _stopBits; } set { _stopBits = value; } } /// <summary> /// property to hold the DataBits /// of our manager class /// </summary> public string DataBits { get { return _dataBits; } set { _dataBits = value; } } /// <summary> /// property to hold the PortName /// of our manager class /// </summary> public string PortName { get { return _portName; } set { _portName = value; } } /// <summary> /// property to hold our TransmissionType /// of our manager class /// </summary> public TransmissionType CurrentTransmissionType { get { return _transType; } set { _transType = value; } } #endregion #region Manager Constructors /// <summary> /// Constructor to set the properties of our Manager Class /// </summary> /// <param name="baud">Desired BaudRate</param> /// <param name="par">Desired Parity</param> /// <param name="sBits">Desired StopBits</param> /// <param name="dBits">Desired DataBits</param> /// <param name="name">Desired PortName</param> public Comm(string baud, string par, string sBits, string dBits, string name) { _baudRate = baud; _parity = par; _stopBits = sBits; _dataBits = dBits; _portName = name; //now add an event handler comPort.DataReceived += new SerialDataReceivedEventHandler(comPort_DataReceived); } /// <summary> /// Comstructor to set the properties of our /// serial port communicator to nothing /// </summary> public Comm() { _baudRate = "9600"; _parity = "None"; _stopBits = "1"; _dataBits = "8"; _portName = "COM4"; //add event handler comPort.DataReceived += new SerialDataReceivedEventHandler(comPort_DataReceived); } #endregion #region WriteData public void WriteData(string msg) { switch (CurrentTransmissionType) { case TransmissionType.Text: //first make sure the port is open //if its not open then open it if (!(comPort.IsOpen == true)) comPort.Open(); //send the message to the port comPort.Write(msg); //display the message DisplayData(MessageType.Outgoing, msg + "\n"); break; case TransmissionType.Hex: try { //convert the message to byte array byte[] newMsg = HexToByte(msg); //send the message to the port comPort.Write(newMsg, 0, newMsg.Length); //convert back to hex and display DisplayData(MessageType.Outgoing, ByteToHex(newMsg) + "\n"); } catch (FormatException ex) { //display error message DisplayData(MessageType.Error, ex.Message); } finally { } break; default: //first make sure the port is open //if its not open then open it if (!(comPort.IsOpen == true)) comPort.Open(); //send the message to the port comPort.Write(msg); //display the message DisplayData(MessageType.Outgoing, msg + "\n"); break; break; } } #endregion #region HexToByte /// <summary> /// method to convert hex string into a byte array /// </summary> /// <param name="msg">string to convert</param> /// <returns>a byte array</returns> private byte[] HexToByte(string msg) { //remove any spaces from the string msg = msg.Replace(" ", ""); //create a byte array the length of the //divided by 2 (Hex is 2 characters in length) byte[] comBuffer = new byte[msg.Length / 2]; //loop through the length of the provided string for (int i = 0; i < msg.Length; i += 2) //convert each set of 2 characters to a byte //and add to the array comBuffer[i / 2] = (byte)Convert.ToByte(msg.Substring(i, 2), 16); //return the array return comBuffer; } #endregion #region ByteToHex /// <summary> /// method to convert a byte array into a hex string /// </summary> /// <param name="comByte">byte array to convert</param> /// <returns>a hex string</returns> private string ByteToHex(byte[] comByte) { //create a new StringBuilder object StringBuilder builder = new StringBuilder(comByte.Length * 3); //loop through each byte in the array foreach (byte data in comByte) //convert the byte to a string and add to the stringbuilder builder.Append(Convert.ToString(data, 16).PadLeft(2, '0').PadRight(3, ' ')); //return the converted value return builder.ToString().ToUpper(); } #endregion #region DisplayData /// <summary> /// method to display the data to & from the port /// on the screen /// </summary> /// <param name="type">MessageType of the message</param> /// <param name="msg">Message to display</param> [STAThread] private void DisplayData(MessageType type, string msg) { //Console.WriteLine("~!~!~! Com4 Data: " + msg); String[] msgParts = msg.Split(','); try { double xDouble = Convert.ToDouble(msgParts[0]); xVal = (float)xDouble; } catch (Exception e) { } try { double yDouble = Convert.ToDouble(msgParts[1]); yVal = (float)yDouble; } catch (Exception e) { } } #endregion #region OpenPort public bool OpenPort() { try { //first check if the port is already open //if its open then close it if (comPort.IsOpen == true) comPort.Close(); //set the properties of our SerialPort Object comPort.BaudRate = int.Parse(_baudRate); //BaudRate comPort.DataBits = int.Parse(_dataBits); //DataBits comPort.StopBits = (StopBits)Enum.Parse(typeof(StopBits), _stopBits); //StopBits comPort.Parity = (Parity)Enum.Parse(typeof(Parity), _parity); //Parity comPort.PortName = _portName; //PortName //now open the port comPort.Open(); //display message DisplayData(MessageType.Normal, "Port opened at " + DateTime.Now + "\n"); //return true return true; } catch (Exception ex) { DisplayData(MessageType.Error, ex.Message); return false; } } #endregion #region comPort_DataReceived /// <summary> /// method that will be called when theres data waiting in the buffer /// </summary> /// <param name="sender"></param> /// <param name="e"></param> void comPort_DataReceived(object sender, SerialDataReceivedEventArgs e) { //determine the mode the user selected (binary/string) switch (CurrentTransmissionType) { //user chose string case TransmissionType.Text: //read data waiting in the buffer string msg = comPort.ReadExisting(); //display the data to the user DisplayData(MessageType.Incoming, msg + "\n"); break; //user chose binary case TransmissionType.Hex: //retrieve number of bytes in the buffer int bytes = comPort.BytesToRead; //create a byte array to hold the awaiting data byte[] comBuffer = new byte[bytes]; //read the data and store it comPort.Read(comBuffer, 0, bytes); //display the data to the user DisplayData(MessageType.Incoming, ByteToHex(comBuffer) + "\n"); break; default: //read data waiting in the buffer string str = comPort.ReadExisting(); //display the data to the user DisplayData(MessageType.Incoming, str + "\n"); break; } } #endregion } }

C# Source Code
Game.cs
Comm comm = new Comm(); private void LoadGameContent() { comm.OpenPort(); } private void HandleInput(GameTime gameTime) { // comm.xVal & comm.yVal determine movement and steering }

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