CIRCUIT DESCRIPTION
3-2
11
LCD
Components: 1101
The LCD module (Wintek) is a STN type 100x160 pixel including the driver HD66421 of Hitachi. The touchscreen is glued on
top the the LCD module.
The LCD module uses a 8 bit bus directly iterfacing to the databus of the master.
It uses two voltages: 3.3V for the logic and 17V for the LCD glass drive.
The LCD driver uses a clock of approx. 190kHz to generate all timing.
12 Keyboard
Components: 0102, etc...
The keyboard is a matrix of 6 x 3 keys. It is static when no key is pressed, and scanned when a key is applied.
13 Slave microcontroller
Components: 7301
The slave microcontroller M37540M4 (Mitsubishi) takes most of the real-time functions: IR-sending, IR learning and steering
the database microcontroller.
Sending IR is performed via pins 28 and 29, combining envelope and carrier with AND-gate 7302.
Transistors 7303 and 7304 combine the IR-sending signals from slave uC and database uC towards the IR-transmitter circuit.
The salve uC also switches on/off the power of the learing circuit via 7305.
Bidirectional communication to the master uC goes via a UART at 57kBaud.
Communication to the database uC goes via a 3-line dedicated bus.
14 Infrared transmitter
Components: around 7307, 7308
The IR-transmitter transmits any IR-code coming from slave or database uC.
It steers two IR-transmission diodes with a peak current of approx. 300mA in each of them.
The IR-diodes transmit invisible infrared light at 940 nm in an angle of 2 x 25 degr.
An electrolytic capacitor of 100uF smoothen-out the carrier frequency in order to have only the average current flowing from
the batteries (envelope of the IR-code).
There are many many brands with each several IR-codes. Basically, all codes consist of a low bitrate burst (around 1kbit or
slower) modulated on a carrier of 30 - 60kHz, and repeated at a rate of 5 - 20Hz.
15 Learning circuit
Components: around 7309, 7310
This circuit is used for learning IR-codes. It uses signals captured by the IR-transmission LEDs 6301and 6302. Transistor
7309 amplifies the signal. Opamp LM393-B puts a minimum threshold and amplifies further. The output of LM393-B contains
the carrir frequency and is fed to the slave IC for carrier frequency measurement. The output is also fed onto a detector. This
has a time constant suitable to detect to the envelope signal of the IR-code. Opamp LM393-A cleans up and its output is fed
also into the slave uC for envelope recording.
16 IR - Receiver
Infrared receptor 6306 and surrounding components
17 Not impemented functions (in circuit diagram)
Some of the parts in the circuit diagram are actually not stuffed on the board.
RS transmitter module 1301
Overview of frequencies
EL-foil driver D371A: 17kHz, 500Hz (75Vpeak)
+/-17V generator: 150kHz, 3MHz ringing
crystals master uC: 7.3728MHz, 32.768kHz
resonator slave uC: 3.64MHz
resonator database uC: 4MHz
RS232 speed: 115kBaud
baudrate between master & slave uP: 57.6kBaud
LCD internal clock: 190kHz
IR-transmission: carrier frequencies: approx. 30 - 60kHz
List of EMC-critical components
Critical components for EMC are:
·
The EL-foil generator (high voltage)
·
All crystals
·
The data & address busses of the master uC to the Flash, SRAM and LCD module
·
The IR-transmitter (high current)
