Hardware
1.9 Functions of the Keypad Adapter
1. To scan the keypad
The keypad adapter scans the keypad and reports the scanned key code to the
main board.
2. To control the LCD brightness
The keypad adapter receives the instructions from the main board to turn on/off
the backlights and power indicator of the LCD and to control the brightness of
the backlights.
3. To control the buzzer
The keypad adapter receives the instructions from the main board to turn on/off
the buzzer.
1.9 .1 Architecture of the Adapter
The adapter mainly consists of a MCU, keypad matrix, backlight control, power
indicator control and buzzer.
1.9.2 Detailed Description
1.9.2.1 Power supply
The main board provides a +12V and 3.3V supplies, which are isolated from
each other. The 3.3V supply is the main power of the adapter and the +12V is
passed to the backlight board (inverter) of the LCD and also converted to a 5V
supply to drive the buzzer and controls the on/off of the backlight power the
adapter. Since the 3.3V and +12V are isolated, the MCU send the control
signals to the buzzer and backlight board through photocouplers.
1.9.2.2 MCU
The MCU is AT89C2051 whose resetting time is 470ms. It uses a 11.0592MHz
crystal oscillator.
1.9.2.3 Keypad scanning
The keypad matrix is 5X4 one, incorporating 9 I/O wires and 20 keys. Note that
the keys at line 5 and columns 3 and 4 are not used.
1.9.2.4 Backlight control
The keypad adapter shuts off the backlight and blinks the power indicator when
instructed by the main board to do so (usually after the analyzer entered the
screen saver). The backlight board uses an independent 12V power supply and
receives the control signals through photocouplers. The transistor is used to
help control the LED so that the power indicator can be turned on even when
something is wrong with the MCU.
1-16 BC-2800 Auto Hematology Analyzer (V1.0)
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