YCL-6 makes the full use of the single-chip resources which is featured with the function of alarm clock, countdown clock, stopwatch and counter.

1. Principle of Operating
The circuit is mainly composed by the single-chip circuit, display circuit, keyboard input, signal ringing circuit and power circuit.
1.single-chip circuit: It's based on AT89C2051 which including the Power-on Reset and clock circuit.
2. Display Circuit: The main component is 2-bit digital tube in red. The driver uses the PNP transistor and it's equipped with current-limiting resistance at every port. It's with scanning-driven way and uses P1.0~P1.6. The colon part use four pieces of diode in Φ3 red with scanning-driven way. And it uses P1.7.
3. keyboard input: The key S1~S3 are with reused function which reused with the display part of P3.5，P3.4 and P3.2. And here is the operating principle.
Output high level at the related PIN to read out the status of keys and debounce via single-chip system to give the keys with corresponding value.
4. Signal Ringing circuit: It's composed by buzzer and PNP transistor. And the operating principle is that the buzzer will send sound in fixed frequency after the PNP transistor turns on. It's with independent port-driven way and uses P3.7. J1 is used for connecting the extrocontrol equipments which will output the low level when there is no ringing signal, or high level with ringing signal.
5. Power Circuit: It's composed by three terminal integrated circuit which will supply the whole system with the stable voltage.


2. Operating Specification
1) Specification of function Keys
S3 is for function choosing key , S2 for function expansion and the S1 for adding the value with one.
2) Operating
It works well if all the components are welded in the right way. And the operating DC voltage is 7V--12V. Please be noted the polarity when connect the power. During the operation, below six functions can be chosen to work, if press the S3 continuously in a short time. And the interval is less than 1 second. Or it goes to the clock function if press the S3 for more than 2 seconds.

Clock Function:
It displays 10：10：00 when it's on.

Time checking Function:
The time and colon start flashing after Press the S3 for a short time. Press S2 to add one hour and Pree S1 to add 1 minute. But the second time is unadjustable.

Alarming Function:
It displays 22：10：00 and the colon lights after press S3 twice in a short time. Press S2 to add one hour and Pree S1 to add 1 minute. But the second time is unadjustable. When the value of hour is over 23:00pm, it displays ——：——：—— which is the function for turn off the alarming function.

Countdown Function:
It displays O and the colon is in dark after 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 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.

Stopwatch Function:
It displays 00：00：00 and the colon lights after press S3 four times in a short time. It starts clocking with the stopwatch after pressing S2. And if press S2 one more time, the clocking will be end. And the stopwatch goes to reset status after pressing S1 at this time.

Counter Function:
It displays 00：00：00 and the colon is in dark after press S3 five times in a short time. Press S2 to add the value with one for counter and Pree S1 to let the counter in reset status.






4. List of Components
Order Item Name Specifications Code Item Order Item Name Specifications Code
1 Resistor 1K R9~R15 20 S8550 Q1
2 1K R2~R8 21 Transistor S8550 Q2
3 2K R16~R17 22 S8550 Q3
4 5.1K R18 23 S8550 Q4
5 10K R1 24 S8550 Q5
6 Ceramic Capacitor 30P C2 25 S8550 Q6
7 30P C3 26 S8550 Q7
8 104 C4 27 Single-chip Circuit AT89C2051 U1
9 104 C5 28 Three Terminal IC 78L05 U2
10 Electrolytic Capacitor 10uF/25V C1 29 Quartz Crystal 12MHz Y1
11 100uF/16V C6 30 IC Socket XH2.54(Horizontal) 2P J2
12 LED Φ3 Red-to-Red D1 31 XH2.54(Vertical) 2P J1
13 Φ3 Red-to-Red D2 32 Keys 6*6*4.3 S1
14 Φ3 Red-to-Red D3 33 6*6*4.3 S2
15 Φ3 Red-to-Red D4 34 6*6*4.3 S3
16 Digital Tube 4 inches 2-bit Red DS1 35 IC Socket 20P U1
17 4 inches 2-bit Red DS2 36 PCB 49*97.5mm 1
18 4 inches 2-bit Red DS3 37 Power Wire 2P (Single)150mm 1
19 Buzzer 5V U3 38