This is yet another digital clock kit built with AT89C2051-24PU chip. We have previously made several digital clock kits for beginners and hobbyists. The kit comes with all the components required.
The schematic of the kit:
The kit uses the full use of a single-chip AT89C2051 that makes an alarm clock, countdown clock, stopwatch, and a counter.
How does the kit work
The circuit consists of a single-chip circuit, display circuit, keyboard input, alarm/buzzer circuit, and a power circuit.
1. Single-chip circuit: It’s based on AT89C2051 which includes a power-on reset and clock circuit.
2. Display Circuit: The main component is the 2-bit seven segment display in red color. The driver uses the PNP transistor 8550 and it’s equipped with current-limiting resistance at every port.
3. Tactile switches input: The key S1, S2, and S3 are for setting up time and alarm.
4. Buzzer ringing circuit: It consists of a buzzer and a PNP transistor. The buzzer will produce sound in a fixed frequency after the PNP transistor turns on. J1 is used for connecting the extra control equipment which will output a low level when there is no ring signal or high level with a ring signal.
5. Power Circuit: It’s composed of three-terminal integrated circuits, which is LM7805 (a 5V voltage regulator) which will supply the whole system with the stable voltage.
It works well if all the components are soldered in the right way. The operating DC voltage is 7V-12V. Please be careful with the polarity while connecting the power.
It displays 10：10：00 when it’s turned on.
Time checking Function:
The time and colon start flashing after you press the S3 for a short time. Press S2 to add one hour and Pree S1 to add 1 minute. The second time is unadjustable.
It displays 22：10：00 and the colon lights up after you press S3 twice in a short time. Press S2 to add one hour and Pree S1 to add 1 minute. The second time is unadjustable. When the value of hour is over 23:00 pm, it displays ——：——：—— which is the function for turning off the alarming function.
It displays O and the colon are off after you press S3 three times in a short time. The hour time is added after pressing S2 and 1 minute is added after pressing S1. It’ll start to countdown when you press S2 for the sixth time. The time can be adjusted again after pressing S2 for one more time. And the countdown function is off.
It displays 00：00：00 and the colon lights after pressing S3 four times in a short time. It starts clocking with the stopwatch function after pressing S2. And if you press S2 one more time, the clocking will end. And the stopwatch goes to reset status after pressing S1.
It displays 00：00：00 and the colon is off after pressing S3 five times in a short time. Press S2 to add the value with one for counter and press S1 to let the counter in reset status.
The following images should guide you to assemble the kit properly. You can see all the images on Flickr also.
The following images will display what you will get in the kit package: