Design of quartz digital clock based on LM8560

A digital clock is a device that uses digital circuit technology to realize the timing of hours, minutes and seconds. The design process of a traditional digital clock goes through three stages: design proposal, solution verification and modification. It is generally carried out by bridging experimental circuits, which often requires repeated experiments and modifications until the correct conclusion is designed, such as the circuit design of a multifunctional digital clock in the reference. With EDA tools, electronic designers can design electronic systems from concepts, algorithms, protocols, etc. A lot of work can be done by computers, and the entire process of electronic products from circuit design, performance analysis to IC layout or PCB layout design can be automatically processed on the computer.

Electronic products can be designed from system design, circuit design to chip design and PCB design using EDA tools, among which simulation analysis, rule checking, automatic layout and automatic wiring are the most effective parts where computers replace manual work. Using EDA tools can greatly shorten the design cycle, improve design efficiency and reduce design risks.

Protel99SE is a 32-bit PCB design software package with powerful design functions that can complete schematics, PCB design and programmable logic device design.

1 Working principle of digital clock

Digital timers are generally composed of oscillators, frequency dividers, counters, decoders, displays, etc. These are the most widely used circuits in digital circuits, and their composition block diagram is shown in Figure 1.

2 Counting and decoding LM8560 components

The counting and decoding part uses the LM8560 component. The LM8560 is a PMOS large-scale integrated circuit, which is encapsulated in a dual-in-line plastic package and equipped with a 4-digit digital display board. Its equivalent principle block diagram is shown in Figure 2. Features: drive 7-segment LED light-emitting tube display; 50/60Hz operation; 12/24-hour display; 12-hour display AM (morning) and PM (afternoon) indication; advanced zero shutdown; 9-minute snooze alarm; preset 59 minutes (or 1 hour and 59 minutes) sleep timer; preset alarm within 24 hours; use touch incrementer to set control; power failure indication; backup RC oscillator; 900 Hz music output.

1) 50/60 Hz output selection The AC power frequency used in China is 50 Hz. Just connect pin 26 (50/60Hz selection) to Vss. If the power frequency is 60 Hz, this pin is left floating.

2) 12/24 hour display selection Connect pin 28 (12/24 hour selection) to Vss to display in 24 hour format; leave this pin unconnected to display in 12 hour format.

3) When the CR input is powered off, the backup battery automatically supplies power, and the clock oscillator inside the chip immediately works to replace the 50/60 Hz input, and the control time counter continues to count, but does not display; when the power is on, it automatically switches to AC power and resumes display. In this way, even if there is a power outage, it can still accurately count. The values ​​of R and C connected to the CR input determine the frequency of the clock oscillator inside the chip. The stability of the backup oscillator is ±10% and the accuracy is ±10%.

4) 50/60 Hz input The time base of the time counter is input from this terminal (pin 25) when the 50/60 Hz AC power supply is provided. This terminal is connected to a simple RC filter circuit to eliminate the influence of power supply voltage transients, otherwise it is easy to cause clock misrecording or device damage.

5) Display mode selection Use the SPST switch to select one of the four displays: time, seconds, alarm time, and sleep time.

6) Time Setting Input The hour setting and minute setting terminals are used to adjust the time or set the alarm and sleep time. In the sleep display mode, the hour setting can set the sleep timer to 1 hour and 59 minutes, otherwise it will be set to 59 minutes.

7) Power failure indication If the power is turned off and then on again, all strokes flash at a frequency of 1 Hz and can then be restored using the hour setting and minute setting inputs.

8) Alarm output and alarm off input If the alarm setting matches the real time, this output controls the external circuit to emit a 900 Hz tone at 2 Hz. It can last for 1 hour and 59 minutes unless it is reset by the alarm off input or snooze input and returns to normal. In addition, a DC output can be obtained through a simple low-pass filter and used as a control signal.

9) Snooze input During the alarm period, this input can temporarily shut down the alarm for 9 minutes, after which the alarm signal reappears; it can be reused within 1 hour and 59 minutes of the alarm.

10) Sleep timer and input are usually used to automatically turn on the radio within a 59-minute (or 1 hour and 59 minutes) time interval, and the radio automatically turns off after 59 minutes (or 1 hour and 59 minutes). The radio can also be turned off manually using the snooze input.

11) The voltage range applied to any foot of the board limit is: +0.3～-15.0 V, operating temperature: -20℃～+70℃, storage temperature: -55℃～+150℃, maximum lead temperature (soldering 10 s): 300℃.

3. Create a circuit schematic

Draw the digital clock circuit diagram shown in Figure 3 under the Protel99E software platform.

The specific requirements are: the package form of the integrated circuit LM8560 is DIP28; the package form of 4069 is DIP14; the package form of the resistor RES2 is AXIAL0.3; the package form of the capacitor CAP is RAD0.1; the package form of the electrolytic capacitor ELECTRO1 is RB.2/.4; the package form of the crystal oscillator CRYSTAL is XTAL1; the package form of the diode DIODE is DIODE0.4; the package form of the speaker SPEAK-ER is AXIAL0.4; the package form of the switches K1~K5 is AXIAL0.3; the package form of EN-148-28 is homemade.

4. Draw the printed circuit board

1) Perform electrical rules check and create netlist.

2) Plan the printed board and set the document parameters. The printed board size is required to be 100mmx70mm; the visible grid 1 is set to 1mm, the visible grid 2 is set to 10mm, and the capture grid is set to 0.5mm.

3) Load the network table of the schematic diagram. Since the pad number in the diode package is inconsistent with that in the schematic diagram, an error will occur during the loading process. Therefore, the pad number in the package must be modified to be consistent with it, and the PCB must be updated.

4) Manually adjust the layout of components.

5) Set the automatic wiring parameters. The specific requirements are as follows:

Wiring spacing: 0.254 mm;

Wiring turning angle: 45°;

Wiring layer: the top layer is wired vertically, and the bottom layer is wired horizontally;

Wiring width: 1 mm for network GND; 0.5 mm for others;

Automatic wiring is performed, followed by manual adjustment. The circuit after wiring is shown in Figure 4.

6) Use 3D to observe whether the printed circuit board design is reasonable. The 3D diagram of the digital clock printed circuit board is shown in Figure 5.

5 Conclusion

This system is based on the design method of EDA technology. It proposes a design scheme of a quartz digital clock using PMOS large-scale integrated circuit LM8560 as a counting decoder. The schematic diagram is created and the printed circuit board is drawn under the Protel99SE software platform, realizing basic timing display and setting, adjusting time and alarm functions. It solves the problem of automatically processing the entire process of digital clock from circuit design, performance analysis to designing PCB board (printed circuit board) diagram on the computer, thereby shortening the design cycle, improving design efficiency and reducing design risks. Make the designed digital clock printed circuit board, install the circuit according to the schematic diagram, and finally install the shell, and a digital quartz clock is ready, as shown in Figure 6. Researching digital clocks and expanding their applications has very practical significance.