In this project, we'll design a simple digital clock using the CD4020BE, a 14-stage binary ripple counter, and other basic electronic components. The CD4020BE is ideal for counting purposes and is commonly used in frequency division and timing circuits. This project will demonstrate how to use this IC to create a simple digital clock.
Components Required:
● CD4020BE (14-stage binary ripple counter)
● 7-segment display (common cathode)
● Resistors (220Ω and 10kΩ)
● Capacitors (100nF)
● Diodes (1N4148)
● Transistors (2N2222 or similar)
● Push-button switches (for reset)
● 5V DC power supply (can be a battery pack or adapter)
● Breadboard and jumper wires
● LED for power indication (optional)
Project Overview:
This project will use the CD4020BE as the core counter to drive a digital clock. The 14-stage counter in the CD4020BE allows us to divide down high-frequency pulses into smaller time intervals. We'll also use 7-segment displays to show the time in hours and minutes.
In our setup, we'll design a basic 24-hour clock that displays hours and minutes on two 7-segment displays. A simple reset button will allow us to reset the clock to 00:00. The clock will be driven by a stable 1Hz pulse, which can be derived from an external oscillator or crystal.
Circuit Design:
1. Understanding the CD4020BE:
The CD4020BE is a 14-stage ripple counter IC, meaning it counts from 0 to 16383 in binary. The IC has two inputs:
● Clock (pin 10): This is where the clock pulse is fed in.
● Reset (pin 12): This is used to reset the counter back to 0.
We can utilize the 14 outputs from the CD4020 to represent time intervals (seconds, minutes, and hours). In our case, we'll use the lower bits (Q0, Q1, Q2) for seconds, the higher bits (Q3, Q4, Q5) for minutes, and further bits for hours.
2. Setting Up the Oscillator:
Since we need a stable pulse, we'll use an external 1Hz oscillator to drive the CD4020. One possible option is to use a 555 timer IC configured in astable mode to generate a 1Hz pulse, which will act as our clock signal.
The 555 timer should be connected to the clock input of the CD4020BE, providing a steady pulse to increment the counter.
3. Dividing Time into Hours and Minutes:
We will connect the relevant output pins from the CD4020BE to the 7-segment displays to show the time. However, the CD4020 counts in binary, so we need to implement a simple logic to convert the binary values to decimal format for easy display on the 7-segment displays.
The Q0, Q1, Q2 pins will be used to drive the seconds count, while the Q3, Q4, Q5 pins will drive the minutes. We'll use a pair of 7-segment displays to show the time.
4. Connecting the 7-Segment Displays:
Each 7-segment display has 7 LEDs that can be turned on or off to form numbers. We'll wire the 7-segment displays in such a way that each segment is driven by a logic level from the CD4020. The segments are:
● A, B, C, D, E, F, G.
We need a decoder circuit that translates the binary count from the CD4020 into a format that can light up the correct segments on the display. For this, we can use a 74LS47 BCD to 7-segment decoder IC, which simplifies the conversion process.
5. Reset Button:
We'll also incorporate a reset functionality into the design. This is done by connecting a push-button switch to the reset pin of the CD4020BE. When the button is pressed, it will reset the counter to 0000, effectively setting the clock back to 00:00.
The reset circuit will be wired so that when the button is not pressed, the counter continues to increment. When pressed, the reset pin will be pulled low, clearing the counter and starting the clock from zero.
6. Displaying Time:
Once the counter starts running, the Q0, Q1, Q2 and Q3, Q4, Q5 outputs will provide a count that is displayed on the 7-segment displays. The time in seconds will be shown on the first display, and the time in minutes on the second display.
We will wire up the 7-segment displays to the outputs of the BCD decoder ICs, which will take the 4-bit binary values from the CD4020 and convert them into decimal numbers for display.
7. Transistors for Driving the Display:
Since the current required to drive a 7-segment display can be high, we’ll use small transistors like 2N2222 to drive the segments. The transistor will act as a switch, allowing enough current to flow through each segment of the display when activated.
Step-by-Step Assembly:
- Set Up the 555 Timer Oscillator:
● Connect a 555 timer in astable mode to generate a 1Hz clock signal.
● The output of the 555 timer goes to the Clock (pin 10) of the CD4020BE.
- Wire the CD4020BE:
● Connect the Q0, Q1, Q2 pins to the BCD decoder ICs for seconds display.
● Connect the Q3, Q4, Q5 pins to the BCD decoder ICs for minutes display.
● Connect the Reset (pin 12) to a push-button switch to allow for resetting the clock.
- Set Up the 7-Segment Displays:
● Wire the 7-segment displays to the outputs of the BCD decoder IC. Each output from the decoder IC will light up the correct segments to display the numbers.
● Use transistors to drive the 7-segment displays as needed.
- Power the Circuit:
● Connect a 5V power supply to the circuit. If using a battery, ensure it provides a stable 5V output.
- Test the Circuit:
● Once the components are connected, power on the circuit. The 7-segment displays should start showing the time in seconds and minutes.
● Press the reset button to see if the clock resets to 00:00.
Final Thoughts:
This DIY digital clock project demonstrates the versatility of the CD4020BE as a binary ripple counter in creating a simple timing device. By combining this IC with 7-segment displays, BCD decoders, and a 555 timer oscillator, you can create an effective and functional clock.
While this design is basic, it offers a great introduction to digital logic, timing circuits, and display interfacing. You can extend the project by adding additional features, such as a second 7-segment display for seconds, or converting it into an alarm clock with more advanced components.
The simplicity of the CD4020BE makes it an excellent choice for beginners looking to build a functional project, and it can serve as a stepping stone for more complex projects in the world of digital electronics.