Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK 데이터 시트
제품 코드
AT91SAM9N12-EK
871
SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]
11063K–ATARM–05-Nov-13
42.7.3 4-wire Position Measurement Method
As shown in
, to detect the position of a contact, a supply is first applied from top to bottom. Due to the linear
resistance of the film, there is a voltage gradient from top to bottom. When a contact is performed on the screen, the
voltage propagates at the point the two surfaces come into contact with the second film. If the input impedance on the
right and left electrodes sense is high enough, the film does not affect this voltage, despite its resistive nature.
voltage propagates at the point the two surfaces come into contact with the second film. If the input impedance on the
right and left electrodes sense is high enough, the film does not affect this voltage, despite its resistive nature.
For the horizontal direction, the same method is used, but by applying supply from left to right. The range depends on the
supply voltage and on the loss in the switches that connect to the top and bottom electrodes.
supply voltage and on the loss in the switches that connect to the top and bottom electrodes.
In an ideal world (linear, with no loss through switches), the horizontal position is equal to:
VY
M
/ VDD or VY
P
/ VDD.
The implementation with on-chip power switches is shown in
. The voltage measurement at the output of the
switch compensates for the switches loss.
It is possible to correct for switch loss by performing the operation:
[VY
P
- VX
M
] / [VX
P
- VX
M
].
This requires additional measurements, as shown in
Figure 42-7. Touchscreen Switches Implementation
X
P
X
M
Y
M
VDDANA
Y
P
VDDANA
GND
GND
To the ADC
X
P
X
M
Y
P
VDDANA
GND
Switch
Resistor
Switch
Resistor
Y
P
Y
M
X
P
VDDANA
GND
Switch
Resistor
Switch
Resistor
Horizontal Position Detection
Vertical Position Detection
0
1
2
3