ADXL335 Accelerometer

Accelerometer is a sensor that measure linear acceleration. Today we will use ADXL335 accelerometer, we will write a program to display the measured values of acceleration of all 3 axes.

ADXL335 on a board(Manufactured by Sparkfun.com)

You can see axis scheme on the board, the x and y axises directions are clear, and the z axis direction is point out of the board. Remember this sensor has a sensing range of +/-3g, so you can't measure a higher accelerations :). But it is not a big disadvantage, because the calculation shows that more than 100 km/h we can get during 1 second of 3g acceleration. If you want to check it but you are lazy to do, you can use http://www.wolframalpha.com(3 * gravitational acceleration * 1 second in km/h).
The interface of this device is analog: The voltages on X(Y,Z) port depends on the linear acceleration throughout X(Y,Z) axis. The Arduino board has 6 analog-in ports, we can use 3 of them(0,1,2) to connect to X,Y,Z ports of ADXL335.

Analog ports

So lets open the Arduino IDE and write a simple program, which will periodically read the values on analog ports and send trough the Serial port.

	const int xpin = 0;
	const int ypin = 1;
	const int zpin = 2;
	void setup()
	{
	Serial.begin(9600);
	}
	void loop()
	{
	Serial.print("BEG");
	Serial.print("X"); Serial.print(analogRead(xpin));
	Serial.print("Y"); Serial.print(analogRead(ypin));
	Serial.print("Z"); Serial.print(analogRead(zpin));
	Serial.println();
	delay(50);
	}

view raw 1.pde hosted with ❤ by GitHub

In this program analogRead function read the voltage on the pin and return the integer value between 0 and 1023.
On the computer side we will read the information coming through Serial port an show the values on 3 horizontal progress bars.

This is C# code of program

	using System;
	using System.Collections.Generic;
	using System.ComponentModel;
	using System.Data;
	using System.Drawing;
	using System.Linq;
	using System.Text;
	using System.Windows.Forms;
	using System.IO.Ports;
	using System.Threading;
	namespace ADXL335
	{
	public partial class Form1 : Form
	{
	public Form1()
	{
	InitializeComponent();
	}
	private SerialPort serial_port_;
	private Thread thread_;
	private void refresh_button_Click(object sender, EventArgs e)
	{
	portlist_comboBox.Items.Clear();
	foreach (string s in SerialPort.GetPortNames())
	{
	portlist_comboBox.Items.Add(s);
	}
	}
	private void connect_button_Click(object sender, EventArgs e)
	{
	if ("Connect" == connect_button.Text)
	{
	if (-1 == portlist_comboBox.SelectedIndex)
	{
	MessageBox.Show("Select com port");
	return;
	}
	string port_name = portlist_comboBox.SelectedItem.ToString();
	serial_port_ = new SerialPort(port_name, 9600);
	serial_port_.Open();
	thread_ = new Thread(read_serial_port);
	thread_.Start();
	connect_button.Text = "Disconnect";
	}
	else
	{
	try
	{
	thread_.Abort();
	serial_port_.Close();
	}
	catch
	{
	}
	connect_button.Text = "Connect";
	}
	}
	private void read_serial_port()
	{
	while (serial_port_.IsOpen)
	{
	try
	{
	string str = serial_port_.ReadLine();
	set_axis(str);
	}
	catch (TimeoutException) { }
	}
	}
	delegate void SetTextCallback(string newText);
	private string str_;
	private void set_axis(string text)
	{
	if (this.X_progressBar.InvokeRequired)
	{
	SetTextCallback d = new SetTextCallback(set_axis);
	this.Invoke(d, new object[] { text });
	}
	else
	{
	str_ += text;
	int i1 = str_.IndexOf("BEG");
	int i2 = str_.IndexOf("BEG", 1 + i1);
	if ((-1 != i1) && (-1 != i2))
	{
	string current = str_.Substring(0, i2);
	current = current.Substring(current.IndexOf("BEG"));
	str_ = str_.Substring(i2);
	int beg_index = current.IndexOf("BEG");
	int x_index = current.IndexOf("X");
	int y_index = current.IndexOf("Y");
	int z_index = current.IndexOf("Z");
	if ((0 != beg_index) || (3 != x_index) || (-1 == y_index) || (-1 == z_index))
	{
	MessageBox.Show("Error " + current + ", beg_index = " + beg_index.ToString() + ", x_index = " + x_index.ToString() + ", y_index = " + y_index.ToString() + ", z_index = " + z_index.ToString());
	return;
	}
	int x = Convert.ToInt32(current.Substring(x_index + 1, y_index - x_index - 1));
	int y = Convert.ToInt32(current.Substring(y_index + 1, z_index - y_index - 1));
	int z = Convert.ToInt32(current.Substring(z_index + 1));
	if (x > X_progressBar.Maximum) x = X_progressBar.Maximum;
	if (y > Y_progressBar.Maximum) y = Y_progressBar.Maximum;
	if (z > Z_progressBar.Maximum) z = Z_progressBar.Maximum;
	if (x < X_progressBar.Minimum) x = X_progressBar.Minimum;
	if (y < Y_progressBar.Minimum) y = Y_progressBar.Minimum;
	if (z < Z_progressBar.Minimum) z = Z_progressBar.Minimum;
	X_progressBar.Value = x;
	Y_progressBar.Value = y;
	Z_progressBar.Value = z;
	}
	}
	}
	private void Form1_FormClosed(object sender, FormClosedEventArgs e)
	{
	try
	{
	serial_port_.Close();
	}
	catch
	{
	}
	}
	}
	}

view raw 1.cs hosted with ❤ by GitHub

Be careful, connect ADXL335 to the Arduino board, before connecting them to the PC, otherwise the board will hang and only solution is reconnecting.

This is a short video how it runs.