RabbitCore eDisplay OP7200, User Manual

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32 eDisplay (OP7200)
3.4.6 A/D Converter Reference Voltage (+V)
A reference voltage of 2.048 V is generated by the A/D converter chip. The reference volt-
age is used by the touchscreen controller chip, and may also be used to bias the input
attenuator circuits when bipolar inputs are to be measured. As shown in Figure 14, the
factory default is for a surface-mounted 0
Ω
resistor to connect pins 1–2 on header JP8.
This enables the internal reference voltage of 2.048 V generated by the A/D converter chip.
By connecting pins 2–3 on header JP8 instead, a ratiometric reference can be provided by
the divider consisting of R148 and R150. A fixed reference can be configured by remov-
ing R150 and installing a zener diode at U12. The zener diode will then set the reference
voltage. C91 would be always installed, and provides filtering. None of these components
(R148, R150, C91, or U12) is factory-installed.