AKD4184 View Datasheet(PDF) - Asahi Kasei Microdevices

Part Name

Description

Manufacturer

AKD4184

TSC with Keypad Scanner and GPIO Expander

Asahi Kasei Microdevices 

[AK4184]

■ Pen Pressure Measurement

Touch screen pen pressure can be derived from the measurement of the contact resistor between two plates. The

contact resistance depends on the size of the depressed area and the pressure. The area of the spot is proportional to

the contact resistance. This resistance (Rtouch) can be calculated using two different methods.

The first method is when the total resistance of the X-plate sheet is already known. The resistance, Rtouch, is

calculated from the results of three A/D conversions: X-position, Z1-Position, and Z2-Position, using the following

formula:

Rtouch = (Rxplate) * (Xposition/4096) * [(Z2/Z1) – 1]

The second method is when both the resistances of the X-plate and Y-plate are known. The resistance, Rtouch, is

calculated from the results of three A/D conversions: X-position, Y-Position, and Z1-Position, using the following

formula:

Rtouch = (Rxplate*Xposition/4096)*[(4096/Z1) – 1] – Ryplate*[1 – (Yposition/4096)]

AVDD

YP-Driver SW ON

YP

AVDD

YP-Driver SW ON

YP

XP

VREF+

AIN+

ADC

VREF-

AIN-

XN

XN-Driver SW ON

YN

Rtouch

XP

VREF+

AIN+

ADC

VREF-

AIN-

XN

XN-Driver SW ON

YN

a) Z1-Position Measurement

b) Z2-Position Measurement

Figure 4. Pen Pressure Measurements

Rtouch

MS0603-E-00

11

2007/04

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