TTL Digital Clock
To develop DIGITAL CLOCK using 7 segment display. It show hours and minutes. Make it by using discrete components.
A digital clock is a type of clock that displays the time digitally. Digital clocks are often associated with electronic drives, but the “digital” description refers only to the display, not to the drive mechanism.
Basically a digital clock requires these basic elements or blocks
- A source of power to run the clock
- An accurate timebase that acts as the clock’s heartbeat
- A way to gear down the timebase to extract different components of time (hours, minutes, seconds).
A way to display the time
At the heart of the clock there is a piece that can generate an accurate 60-hertz (Hz, oscillations per second) signal. There are two ways to generate this signal:
- The signal can be extracted from the 60-Hz oscillations in a normal power line. Many clocks that get their power from a wall socket use this technique because it is cheap and easy. The 60-Hz signal on the power line is reasonably accurate for this purpose.
- The signal can be generated using a crystal oscillator. Obviously, any battery-operated clock or wristwatch will use this technique instead. It takes more parts, but is generally much more accurate.
The 60-Hz signal is divided down using a counter. A typical TTL part to use is a decade counter. This part can be configured to divide by any number between 2 and 10, and generates a binary number as output. So we take our 60-Hz time base, divide it by 10, divide it by 6 and now we have a 1-Hz (1 oscillation per second) signal. This 1-Hz signal is perfect for driving the “second hand” portion of the display. Similarly by configuring the decade counter we can produce the minute hand and hour hand also.
To actually see the output of the counters we need to drive a display. The two counters produce binary numbers. The divide-by-10 counter is producing a 0-1-2-3-4-5-6-7-8-9 sequence on its outputs, while the divide-by-6 counter is producing a 0-1-2-3-4-5 sequence on its outputs.
We want to display these binary numbers on something called a 7-segment display. A 7-segment display has seven bars on it, and by turning on different bars we can display different numbers. To convert a binary number between 0 and 9 to the appropriate signals to drive a 7-segment display, we use a “binary number to 7-segment display converter.” This chip looks at the binary number coming in and turns on the appropriate bars in the 7-segment LED to display that number.