3-1
CIRCUIT DESCRIPTION
1
Power supply
Components: 7201
The power supply makes use of the LT1761 low drop linear regulator of Linear Technologies. The output voltage is 3.3V.
2
Reset & delayed reset.
Components:
-reset: 7202
-delayed reset: around 7203, 7204
The S-809 (Panasonic) detects the hardware reset level of the batteries. Below this level (2.8V) reset is passed to the
"delayed reset" circuit.
The "delayed reset circuit" is activated by the S-809 or the reset switch 1203. It will delay the reset signal by approx. 80ms and
has a hysteresis of 200mV
3
Battery level measurement
Components: around 7206, 7207
The battery voltage is measured via a 1:2 divider by the master microcontroller. This divider is switched on/off by the master
by means of 7206 and 7207.
4
EL-foil driver
Components: around 7205
The EL-sheet is driven by the D371 (Durel). This component generates a high-voltage semi sinewave by switching a coil of
2.2mH. It contains 2 oscillators: a high-frequency oscillator switching into the inductor at approx. 17kHz. A low-frequency
oscilator drives the EL-sheet at approx. 500Hz. The EL-sheet is driven with approx. 75Vpeak.
Zener diodes 6208 and 6209 limit the sinewave voltage when no sheet is attached (during repair of the unit).
5
+/- 17V generator
Components: around 7210
The + and - 17V are generated by the MC64063A, a DC-to-DC converter who is used in a step-up configuration.
The switching frequency ranges up to 150kHz (depending on the load) with ringing on the edges of approx. 3MHz.
The generator is switched on/off via 7208 and 7209 from the master microcontroller.
6
Master microcontroller & memories
Components: 7101, 7115, 7103, 7102
The master is the main microcontroller in the system (M30800, Mitsubishi). It uses external flash program memory
(AM29LV800BT, AMD) and SRAM (CY62256V, Cypress). Address selection is performed with 74LV139.
The master runs from two crystals: 7.3728MHz, onlu runing when active. The other crystal of 32.768kHz is always running,
even in sleep mode.
7
Buzzer
Components: around 1103
The sound function is made by a piezo-electric buzzer. The steering frequency range is 200Hz ~ 8kHz.
8
RS232 transmitter
Components: around 7105, 7106
This circuit converts the RS232 outgoing signal from the master between 0 and 3.3V to -15 and +15V levels.
RS232 communication is set at 115kBaud both directions.
9
RS232 receiver & detection.
Components: around 7107, 7108, 7109
Transistor 7107 converts the incoming RS232 signals between -/+15V into 0-3V levels towards the master.
Transistors 7108 and 7109 perform a RS232 incoming signal detection and interrupt the master during sleep mode when
communication starts from a connected PC.
10 Touchscreen.
Components: around 7111, 7112, 7113, 7114
A resistive touchscreen is used, composed of two layers of resistive material. Pressing the screen causes a short-circuit
between the two layers.
The touchscreen is operated in two steps:
1. detection of a touch
2. reading of the actual position of the touch
Detection is done by connecting one layer to ground and the second layer to 3.3V with a pull-up resistor. The voltage on the
second layer will change from 3.3V to 0V when touching.
Readout is performed in 2 phases, each determining one coordinate.
First, layer 1 is connected between 3V3 and ground. The potentiometric position of the touch location can be read by
measuring the voltage on the layer 2.
The other coordinate is read by interchanging the layers in previous procedure.
