Electronic clock design based on 74LS90

Looking back on the course design of the 60-digit electronic clock
       , I have a lot of emotions. It lasted 13 weeks. I analyzed the topic on paper, drew it and simulated it on Proteus. I also had a deeper understanding of the chip. The digital electronic clock is very important. It counts at a standard frequency (1Hz) and consists of a second pulse circuit, a counting circuit, a decoding display circuit, and a time correction circuit. 1. When the digital electronic clock is working normally, the crystal oscillator generates a stable pulse signal, which is divided by a frequency divider composed of NE555 and 74LS74 to finally obtain a 1Hz square wave, that is, a second pulse signal. The second pulse signal is sent to a counting circuit composed of multiple 74LS90 chips cascaded as a timing reference signal for counting. The second and minute digits are automatically cleared after the count reaches 60, and the cycle continues. The counting result 8421BCD code is input to the corresponding 4511 decoder for decoding of each hour, minute and second, and is displayed through the LED digital tube. If there is an error between the timing result of the digital electronic clock and the actual time, it can be corrected through the time correction circuit. The time correction circuit consists of a button and a button debounce circuit. Pressing the button can correct the time. Each part of the circuit is connected to form the overall circuit of the digital electronic clock. The ones and tens digits of the minute and second counters respectively correspond to a seven-segment display decoder CD4511 and a semiconductor digital tube, which can display the values ​​of minutes and seconds at any time. The two chips are cascaded; connect the carry end of the high-order chip to the UP end of the next level. This is a 60-digit counter formed by connecting two 74LS90 chips. The low-order chip is connected to become a decimal counter, and its CLK terminal is connected. Is the low carry pulse. The high bit is connected to a hexadecimal counter. When the output terminal is 0101, the data is set to 0000 on the rising edge of the next clock, thus forming a hexadecimal counter. When connected in cascade, it becomes a hexadecimal counter, which can be used as seconds and minutes respectively.
        After completing the simulation design, we use the Jialichuang EDA platform for system debugging. Based on the Proteus simulation diagram, it is not difficult to draw the EDA schematic diagram (as shown below).
       The illustrated part includes the main body of the schematic diagram, the power supply module, and the power indicator light. The schematic diagram we drew on the Jialichuang platform can be directly converted into a PCB template. However, one thing to note is that before conversion, you must check the packaging of each component to ensure that the correct components are used. After converting to a PCB template, you can make a layout design according to your own ideas (as shown below),
3D diagram:
 
        But the layout process must ensure that each original part has an independent space, which can also simplify our next welding part. , after the typesetting is completed, the automatic wiring function can be selected (or manual wiring can be performed by yourself) to complete the production of the PCB board. After checking the DRC, the PCB board can be printed. After making the board, you can directly purchase the components according to the BOM list. After all the preparations are completed and confirmed, the components can be welded. The order of component welding is first difficult and then easy, first low and then high. The general welding sequence is the welding of resistors, capacitors, diodes, transistors, manifolds, high-power and other components. When welding the manifold, first weld the two pins on the side of the manifold to position it, and then weld each lead angle from top to bottom and from left to right. Be careful not to reverse the positive and negative poles of the capacitor and LED light.
 Welding physical board display:
actual operation display:
(original)