AVR1909
3
8297A-AVR-04/10
The Display Xplained module is quite simple. It basically connects the TFT display
SPI interface, resistive touch interface, and backlight interface from a 40pin FPC
connector to two female pin-headers that fit the Xplain kit.
In addition it has a program/debug interface that will connect an external
programmer/debugger to the Xplain kit through a male and a female pin-header.
3.1 The LCD Module The LCD module is produced by EDT (Emerging Display Technologies Corp), and is
called ET024006DHU. It will be replaced with a new version called ET024008DHU in
mid 2010 that have the same outline dimension and same electronics and optical
specification.
The LCD module embeds a graphical controller/driver from Himax called HX8347-A.
This controller provides several communication interfaces like 8/16bit parallel MCU
interface, 16/18bit RGB, and 4-wire serial SPI interface. On the Display Xplained
module this has been hardwired to use serial SPI interface.
The display is attached to the PCB with a strong dual-sided foam tape adhesive that
make it easy to mount. This will electrically insulate the display from the PCB avoiding
any short-circuit problems that may be caused by vibration wearing on the solder
mask and tracks/vias. It will also provide some vibration damping for the display to
protect the glass surface from cracking. It is also quite easy to remove the display if
needed.
3.2 The Touch module The LCD module has a 4-wire resistive touch interface. This consists of four lines (2
in each X and Y direction) that should be connected to ADC/IO pins on the MCU
interfacing it. The general procedure is to apply a voltage (VCC) for instance on the
X-lines and then measure the voltage on the Y-lines. Then the operation is repeated,
but switching the X and Y lines. This will give a (X,Y) coordinate for the touch.
In order to avoid over driving (saturate) the ADC inputs, serial resistors have been
added so the maximum voltage is within the ADC capability. This is a very simple and
low-cost solution to adjust the touch sensor output to fit the ADC inputs. It will also
lower the current consumption a little to increase the overall power performance.
For more details on how to use 4-wire resistive touch sensors, see the application
note AVR341: Four and five-wire Touch screen Controller using tinyAVR® and
megaAVR® devices
3.3 The Backlight module The backlight module of the display consists of three white LEDs connected in
parallel. These can draw up to 60mA and have a maximum voltage drop up to 3.6V.
On the Display Xplained module the backlight is connected to the V3P3 (3.3V) power-
supply. This will somewhat limit the maximum light output in change of a simpler
design.
A MOSFET turns the backlight LEDs on/off and a 4.7ohm resistor limits the maximum
current through the LEDs. This makes it quite easy to control the backlight with a
PWM signal to adjust intensity.