RabbitCore eDisplay OP7200, Руководство пользователя

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User’s Manual 31
3.4.4 Touchscreen
The OP7200 analog touchscreen provides a high-resolution matrix of 4096 × 4096
elements. The touchscreen is mounted to the front of and is the same size as the LCD mod-
ule. A four-conductor flex cable connects the touchscreen to the OP7200 at connector J13.
The inputs from the touchscreen are protected from ESD by ferrite beads, capacitors, and
shunt diodes. The ferrite beads and capacitors also serve to eliminate EMI radiating from
the cable. Ferrite beads rather than resistors are used in series with the inputs to maintain
the most accurate measurement of the touchscreen
x,y position.
A reference voltage is applied across the touchscreen. When the touchscreen is touched,
resistances that represent the
x,y position are presented at the input circuit. The touchscreen
controller chip U9 converts these resistances into digital form for use by the software.
NOTE: Should you touch two or more different points on the touchscreen simultaneously,
the resistance presented to the input circuit will represent some difference between the
resistances corresponding to the points. This can lead to a different or an unknown
key’s value being processed. To prevent this from happening, exercise care to “touch”
only one point or position on the touchscreen at a time.
3.4.5 Analog Supply Voltage
The analog section is isolated from digital noise generated by other components by way of a
low-pass filter composed of L2, C31, and C32 as shown in the left side of Figure 14. The +V
analog power supply powers the A/D converter chip.
Figure 14. Analog Supply and Voltage Reference Circuits
C91
100 nF
R148
100 W
+V
R150
453 W
1
3 2
JP8
ADC Chip
Internal
Reference
Voltage
U12
To
A/D Converter
+V
Vcc
C31
100 nF
C32
100 nF
L2