Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet

872

SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]

11063K–ATARM–05-Nov-13

The method to measure the pressure (Rp) applied to the touchscreen is based on the known resistance of the X-Panel
resistance (Rxp).

Three conversions (Xpos,Z1,Z2) are necessary to determine the value of Rp (Zaxis resistance).

Rp = Rxp*(Xpos/1024)*[(Z2/Z1)-1]

To make a 5-wire touchscreen, a resistive layer with a contact point at each corner and a conductive layer are used. 

The 5-wire touchscreen differs from the 4-wire type mainly in that the voltage gradient is applied only to one layer, the
resistive layer, while the other layer is the sense layer for both measurements.

The measurement of the X position is obtained by biasing the upper left corner and lower left corner to V

DDANA 

and the

upper right corner and lower right to ground. 

To measure along the Y axis, bias the upper left corner and upper right corner to V

DDANA 

and bias the lower left corner

and lower right corner to ground.

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

XPos Measure(Yp)

Y

P

Y

M

Open 

circuit

Rp

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

Z1 Measure(Xp)

Y

P

Y

M

Open 

circuit

Rp

X

P

X

M

VDDANA

GND

Switch 

Resistor

Switch 

Resistor

Z2 Measure(Xp)

Y

P

Y

M

Open 

circuit

Rp