AK4185 AKM [Asahi Kasei Microsystems], AK4185 Datasheet - Page 10

• Manufacturer Part Number: AK4185
• Manufacturer: AKM [Asahi Kasei Microsystems]

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The 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 that when the total resistance
of the X-plate sheet is already known. The resistance, Rtouch, is calculated from the results of three conversions,
X-position, Z1-position, and Z2-position, and then using following formula:
The second method is that when both the resistances of the X-plate and Y-plate are known. The resistance, Rtouch, is
calculated from the results of three conversions, X-position, Y-position, and Z1-position, and then using the following
formula:
MS0954-E-00
R
R
ADC
TOUCH
TOUCH
Pen Pressure Measurement (Only 4-wire Touch Screen)
VREF+
VREF-
a)
=
=
Z1-Position Measurement Differential Mode
ON
ON
R
R
VDD
X
X
-
-
plate
plate
4096
AIN+
AIN-
⋅
⋅
X
X
4096
Position
Position
⎛
⎜ ⎜
⎝
⎛
⎜ ⎜
⎝
4096
Z
Z
YP
XP
XN
YN
Z
2
1
1
−
1
−
⎞
⎟ ⎟
⎠
1
Figure 5. Pen Pressure Measurements
⎞
⎟ ⎟
⎠
−
R
touch
Y
-
plate
⋅
⎛
⎜
⎝
- 1
- 10 -
Y
ADC
4096
Position
VREF+
VREF-
⎞
⎟
⎠
b)
ON
ON
Z2-Position Measurement Differential Mode
VDD
AIN+
AIN-
YP
XP
XN
YN
touch
[AK4185]
2008/05