Integral Design

This is a second iteration on the device using a Seeed accelerometer as posture sensor that sends alerts when the user’s posture lapses from the position desirable for working extended periods in the seated position.  The previous version used a buzzer on a relay circuit as an alert.  It produced a sound that could drive one to distraction.  This version uses a LED that simply turns red when the user wearing the accelerometer slouches or leans too far from the desirable vertical position.

The modules used in this application are shown in the following screen shot from the .NET Gadgeteer Designer.

Posture Accelerometer Sensor LED Alert

This implementation of the posture sensor is different from the previous version in that it doesn’t require a relay circuit to turn on a buzzer.  It uses the GHI Electronics multicolored LED module.  It also uses the Seeed OLED Display module instead of the larger and more expensive Display T35 from GHI Electronics.

The application logic is similar in this version to the previous except that it omits the relay circuit and turns on the LED instead of the buzzer.  The following illustration shows the working components.

Posture Sensor with LED Alert

The Program.cs file for the application is shown in the following code block.

using System;
using Microsoft.SPOT;

using GT = Gadgeteer;
using Gadgeteer.Modules.Seeed;
using Gadgeteer.Modules.GHIElectronics;

namespace PostureAccelerometerLED
{
    public partial class Program
    {
        void ProgramStarted()
        {
            button.ButtonPressed += new Button.ButtonEventHandler(button_ButtonPressed);
            button1.ButtonPressed += new Button.ButtonEventHandler(button1_ButtonPressed);
            accelerometer.ContinuousMeasurementInterval = new TimeSpan(0, 0, 0, 0, 600);
            accelerometer.MeasurementComplete +=
                new Accelerometer.MeasurementCompleteEventHandler(accelerometer_MeasurementComplete);
            Debug.Print("Program Started");
        }

        void button_ButtonPressed(Button sender, Button.ButtonState state)
        {
            if (button.IsLedOn)
            {
                accelerometer.StopContinuousMeasurements();
                button.TurnLEDOff();
            }
            else
            {
                accelerometer.StartContinuousMeasurements();
                button.TurnLEDOn();
            }
        }

        void accelerometer_MeasurementComplete(Accelerometer sender, Accelerometer.Acceleration acceleration)
        {
            oledDisplay.SimpleGraphics.Clear();

            if (acceleration.Z < 1)
            {
                oledDisplay.SimpleGraphics.DisplayText("Leaning... .",
                    Resources.GetFont(Resources.FontResources.NinaB), GT.Color.Red, 25, 25);
                led.TurnRed();
            }
            else
            {
                led.TurnOff();
            }

            oledDisplay.SimpleGraphics.DisplayText("X: " + acceleration.X.ToString(),
                Resources.GetFont(Resources.FontResources.NinaB), GT.Color.Green, 20, 50);
            oledDisplay.SimpleGraphics.DisplayText("Y: " + acceleration.Y.ToString(),
                Resources.GetFont(Resources.FontResources.NinaB), GT.Color.Green, 20, 75);
            oledDisplay.SimpleGraphics.DisplayText("Z: " + acceleration.Z.ToString(),
                Resources.GetFont(Resources.FontResources.NinaB), GT.Color.Green, 20, 100);
        }

        void button1_ButtonPressed(Button sender, Button.ButtonState state)
        {
            accelerometer.Calibrate();
        }
    }
}

One surprising discovery in this version is that the Accelerometer.StartContinuousMeasurements method has to be set at a lower frequency than the previous version.  Having the relay running on the board changed the configuration so that the button could interupt the continuous measurements and turn off the measurements.  In this version I found that pushing the on/ off button had no effect until I slowed the rate of continuous measurements.

For more details on this scenario, see Posture Regulator using .NET Gadgeteer Accelerometer from Seeed Studio.