Touch Screen

Displays can optionally include a touch overlay so users can interact with the device by touching the screen. Two technologies are common:

• Capacitive — what modern phones use. Accurate, supports multi-touch, no calibration needed. Preferred for new designs.
• Resistive — works through pressure (so usable with gloves) but less accurate and needs calibration.

tip

For a guided start, the Build a Touch UI tutorial wires the capacitive driver below into a complete two-page touch application.

Capacitive

Capacitive panels use a dedicated controller chip on the panel's flat cable, talking to the SITCore over I²C (most common) or SPI. The capacitive displays in GHI Electronics' development options use a FocalTech FT5xx6 controller, supported by the GHIElectronics.TinyCLR.Drivers.FocalTech.FT5xx6 NuGet package.

The driver is interrupt-driven — the panel pulls its interrupt line low when touch data is ready, and the driver reads positions from there, reported in display pixels with no scaling or calibration code needed. The second constructor argument is that interrupt pin; it must match your board's wiring or no events fire (PJ14 on the SCM20260D Dev Board, PG9 on the FEZ Portal). The driver source lives in the TinyCLR-Drivers repo.

The example below subscribes to TouchMove and draws a small ellipse at every reported point:

using GHIElectronics.TinyCLR.Drivers.FocalTech.FT5xx6;

var touch = new FT5xx6Controller(
    i2cController.GetDevice(FT5xx6Controller.GetConnectionSettings()),
    gpioController.OpenPin(SC20260.GpioPin.PJ14)        // Touch interrupt pin (board-specific).
);

touch.Orientation = FT5xx6Controller.TouchOrientation.Degrees0;

touch.TouchMove += (sender, e) => {
    screen.FillEllipse(brush, e.X, e.Y, 5, 5);
    screen.Flush();
};

Orientation lets you rotate the touch coordinate system if the display is mounted at 90°, 180°, or 270° relative to the panel's native orientation.

Resistive

Resistive panels work by sensing the resistance change across X and Y axes when finger pressure shorts the layers together. The TinyCLR driver implements this using GPIO + ADC — four pins to drive the X/Y rails and two ADC channels to read the resulting voltages.

The GHIElectronics.TinyCLR.Drivers.Touch.ResistiveTouch NuGet package wraps the pin sequencing and conversion math:

using GHIElectronics.TinyCLR.Drivers.Touch.ResistiveTouch;

var touch = new ResistiveTouchController(
    screenWidth:  320,
    screenHeight: 240,
    xPlusPin:  SC20260.GpioPin.PA0,         // Digital pin that's also analog-capable.
    yPlusPin:  SC20260.GpioPin.PA3,         // Digital pin that's also analog-capable.
    xMinusPin: SC20260.GpioPin.PA5,         // Digital-only.
    yMinusPin: SC20260.GpioPin.PC3,         // Digital-only.
    adcControllerId: SC20260.Adc.Controller1.Id,
    xAdcChannel: SC20260.Adc.Controller1.PA0,
    yAdcChannel: SC20260.Adc.Controller1.PA3
);

// Calibration — tune to match your specific panel.
touch.ScaleX = new Scale(20, 280);
touch.ScaleY = new Scale(20, 200);

while (true) {
    Thread.Sleep(100);          // Poll every 100 ms.

    var x = touch.X;
    var y = touch.Y;

    if (x >= 0 && y >= 0)
        Debug.WriteLine("X: " + x + ", Y: " + y);
}

The ScaleX and ScaleY properties let you trim the raw ADC range to match your panel — the right values come from a calibration step (touch the four corners, record the readings, work out the mapping).

Choose resistive when you need glove or stylus operation; otherwise capacitive is the better default.