(1) The digital clock serves as a timing device that displays the year, month, day, hour, minute, second, and week. With the advancement of digital integrated circuits and the widespread use of quartz crystal oscillators, the accuracy of digital clocks has far surpassed that of traditional mechanical timepieces. The digitization of timekeeping devices has brought significant convenience to people's daily lives and work, greatly expanding the original functions of watches.
(2) Features such as timed automatic alarms, program-controlled time operations, automatic street light control, power equipment switching, and even the activation of various time-sensitive electronic devices all rely on the digitalization of clocks. Therefore, studying digital clocks and exploring their applications holds great practical importance. This electronic clock is implemented using the AT89S52 microcontroller and an LCD1602 display, allowing users to switch between 12-hour and 24-hour formats using buttons.
Features:
(1) Display of year, month, day, week, hour, minute, and second;
(2) Time adjustment function;
(3) Switching between 12-hour and 24-hour modes;
(4) Hourly chime function.
(1) AT89S52 Microcontroller
(2) LCD1602 Liquid Crystal Display
AT89S52
The LCD1602 comes in two types: backlit and non-backlit. Most models are based on the HD44780 controller. While the backlit version is thicker, there is no functional difference in application. Key technical specifications of the 1602LCD include a display capacity of 16x2 characters, an operating voltage range of 4.5–5.5V, a working current of 2.0mA at 5.0V, and a character size of 2.95×4.35 mm (width × height).
LCD1602 Pin Diagram
Pin 1: VSS – Ground connection.
Pin 2: VDD – Connected to a 5V power supply.
Pin 3: VL – Contrast adjustment pin. When connected to ground, contrast is maximum; when connected to power, it’s minimum. A 10K potentiometer can be used for fine-tuning.
Pin 4: RS – Register select. High level selects data register; low level selects instruction register.
Pin 5: R/W – Read/write signal. High means read, low means write. When both RS and R/W are low, instructions or addresses can be written. When RS is low and R/W is high, busy status can be read. When RS is high and R/W is low, data can be written.
Pin 6: E – Enable signal. When this pin transitions from high to low, the command is executed.
Pins 7–14: D0–D7 – 8-bit bidirectional data lines.
Pin 15: Backlight positive terminal.
Pin 16: Backlight negative terminal.
System Total Circuit Simulation
Module Circuit Design:
The minimal system includes a reset circuit and a clock circuit. The clock circuit provides a 12 MHz signal. The reset circuit uses a manual button to reset the microcontroller without powering it down.
Minimal System
The D0–D7 pins of the LCD are connected to the P0 port of the MCU. Since P0 is used as an output port, external pull-up resistors are required. RS is connected to P2.0, and EN is connected to P2.1. An external 4K potentiometer is used to adjust the display contrast.
LCD Circuit
The module uses a separate keyboard. When a key is pressed, the corresponding I/O port changes from high to low, indicating a key press. Four independent buttons are connected to the P3.0–P3.3 ports of the MCU.
Keyboard Input Function Selection Circuit
The buzzer is used to generate alarm sounds at specific times. The LED lights up when the seconds are even or when a function key is pressed. The buzzer is connected to P2.2, and the LED is connected to P2.3 of the microcontroller.
Buzzer
Software Design Flowchart:
The code should be written as follows:
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