User manual

ECE 477 Final Report Spring 2004
information to the LCD driver memory, monitor the RF transmission line and detect and
debounce button presses. Running at 1MHz is certainly enough to handle these tasks easily,
meaning that no external oscillator is needed.
The graphic LCD display used is the Microtips MTG-S12128XRGNS [2] with and Epson
SED1335 driver [3]. The chief reason for this choice was the fact that the company was willing
to sample the near $60 part. This built-in driver makes operating the LCD and programming text
into memory easy. The display allows for 16 lines of 22 characters each, enabling a menu
system that is not overly complicated by scrolling lists. A simple memory map can be
implemented to allow for constant offsets in menu navigation instead of complex calculations. It
is also possible to incorporate a layer of graphics over the text with minimal effort. A 22 pin
header is all that is required to interface the LCD module to the PCB. The driver contains 8K of
internal SRAM, which is enough to store over 300 lines of text. The only drawback is the need
for a -15V supply to bias the LCD logic voltage. The Maxim MAX776 3.3V to -15V DC to DC
converter [7] is to be used with the Microtips LCD module. This converter requires few external
components, though the large polarized capacitors needed may cause large amounts of noise on
the 3.3V supply powering the microcontroller.
The LCD module also requires a 5V logic supply. The Texas Instruments
SN74LVC4245A octal 3.3V to 5V shifter [4] will be used to interface the 3.3V microcontroller
to the LCD module. This shifter also operates with little power dissipation. Unfortunately, it is
not possible to find a single chip large enough to handle all the data signals the LCD module
requires, so two chips are used.
The RF solution used is the Atmel AT86RF211 smartRF chip [5]. This device accepts a
single serial stream of data and performs all the front and back end processing with few external
components. It is a low cost and low power (3.3V) wireless solution. This device also operates
in the public domain ISM band and performs FSK modulation, a more robust way to handle
noisy environments than the typical OOK method. It is software scalable in transmit power and
takes care of addressing for the microcontroller. If it is ever necessary to improve range or
performance of the remote device it is possible to add SAW filters to the design. There is an
inherent risk in using a reference design to implement our RF transceiver, but this chip is ideal
for our application.
-28-