Integral Design

The relay scenario uses a low-voltage logic circuit to control another circuit, usually of higher voltage.  The relay in this example is a 5 volt DC single pole, single throw reed relay. It is used to switch a battery-driven motor on and off.  The switch is controlled by the Gadgeteer.DigitalOutput interface in a .NET Gadgeteer Visual Studio application.

The schematic for this scenario is shown in the following illustration.

DigitalOutput Relay Circuit

5 volts is supplied by pin 2 of a type X or Y socket on the GHI Electronics Spider mainboard.  The connection in this case is made on a GHI Electronics Extender module.  When the application using the DigitalOutput circuit drives V logic in high, the switch in the relay closes, allowing current to flow from the battery circuit through the motor, M.

This example is based on the same scenario as a previous post; for more information, see Using the .NET Gadgeteer DigitalOutput Interface.

The GT.Interfaces.DigitalOutput object is initialized in the following lines of code.

GT.Socket socket = GT.Socket.GetSocket(4, true, null, "DigitalOutControl");
    control = new GT.Interfaces.DigitalOutput(socket, GT.Socket.Pin.Four, false, null);

Two methods activate the logic high state.

In one case the ButtonEventHandler of a button module starts a timer.  When the GT.Timer.TickEventHandler is raised, an if block writes either true or false in the Gadgeteer.Interfaces.DigitalOutput.Write method. The status of the DigitalOutput object is also shown on the Display_T35 module by the Gadgeteer.Modules.Module.DisplayModule.SimpleGraphicsInterface.DisplayText method.

    void timer_Tick(GT.Timer timer)
    {
        if (control.Read() == true)
        {
            control.Write(false);
            led.TurnGreen();

        }
        else
        {
            control.Write(true);
            led.TurnRed();
        }

        display.SimpleGraphics.Clear();
display.SimpleGraphics.DisplayText("DigitalOutControl: " + control.Read().ToString(),
                Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 50);

    }

The second way to activate the logic high state is the joystick_JoystickPressed event handler, as shown in the following code block. Again the logic state of the DigitalOutput interface is displayed by the Display_T35 module.
Some of the buttons in circulation are glitchy, and I’ve had a few problems with them, so I used the Joystick in this segment.

void joystick_JoystickPressed(Joystick sender, Joystick.JoystickState state)
    {
        if (control.Read()==false)
        {
            control.Write(true);
            led.TurnRed();

            display.SimpleGraphics.Clear();
            display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

        }
        else
        {
            control.Write(false);
            led.TurnGreen();

            display.SimpleGraphics.Clear();
            display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

        }
    }

The running application is shown in the following video segment. First the motor is started by pushing the button to start the timer.  It runs through two ticks before I turn it off.  Next I start the motor by pressing the joystick.

The complete application code follows.

using Microsoft.SPOT;

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

namespace RelayControl
{
    public partial class Program
    {
        GT.Timer timer;
        GT.Interfaces.DigitalOutput control;

        void ProgramStarted()
        {
            GT.Socket socket = GT.Socket.GetSocket(4, true, null, "DigitalOutControl");
            control = new GT.Interfaces.DigitalOutput(socket, GT.Socket.Pin.Four, false, null);

            joystick.JoystickPressed += new Joystick.JoystickEventHandler(joystick_JoystickPressed);
            button.ButtonPressed += new Button.ButtonEventHandler(button_ButtonPressed);

            timer = new GT.Timer(5000);
            timer.Tick += new GT.Timer.TickEventHandler(timer_Tick);

            Debug.Print("Program Started");
        }

        void button_ButtonPressed(Button sender, Button.ButtonState state)
        {
            if (control.Read() == true)
                return;

            if (timer.IsRunning)
            {
                timer.Stop();

                display.SimpleGraphics.Clear();
                display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                    Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

            }
            else
            {
                timer.Start();

                display.SimpleGraphics.Clear();
                display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                    Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

            }
        }

        void joystick_JoystickPressed(Joystick sender, Joystick.JoystickState state)
        {
            if (control.Read()==false)
            {
                control.Write(true);
                led.TurnRed();

                display.SimpleGraphics.Clear();
                display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                    Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

            }
            else
            {
                control.Write(false);
                led.TurnGreen();

                display.SimpleGraphics.Clear();
                display.SimpleGraphics.DisplayText("Timer: " + timer.IsRunning.ToString(),
                    Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 75);

            }
        }

        void timer_Tick(GT.Timer timer)
        {
            if (control.Read() == true)
            {
                control.Write(false);
                led.TurnGreen();

            }
            else
            {
                control.Write(true);
                led.TurnRed();
            }

            display.SimpleGraphics.Clear();
            display.SimpleGraphics.DisplayText("DigitalOutControl: " + control.Read().ToString(),
                    Resources.GetFont(Resources.FontResources.small), GT.Color.Green, 50, 50);

        }
    }
}