Digital Stopwatch 0-99sec

Posted on Feb 4, 2014

We will describe the function of a digital stopwatch, 0 G 99 sec. The function of the stopwatch, relies in the use of 4 integrated circuits, which in this case belong to National Semiconductor ( It is obvious that other integrated circuits can be used to achieve the same result, however in this case we have used the following parts: The circuit that has been used is shown in picture 1.

Digital Stopwatch 0-99sec
Click here to download the full size of the above Circuit.

Through the experimental part we will explain each of the parts function, but in order to have a notion of the basic idea, let just say, that this circuit besides the 5V power supply, is fed with a pulse which comes from a crystal. The crystalG ™s pulse is devided properly in order to obtain the 1 Hz pulse which we need in order for the circuit to work properly, and display the seconds on the 7 segment displays, through a procedure which we will explain through the experimental part. We will begin the description of the digital circuit above. For our convenience we will devide the circuit to 2 parts: the generator, which produces the pulse of the desired frequency, and the part that does the actual counting. The generator of the circuit comprises of the integrated circuits CD4040CM and CD4060CM. We use a crystal which oscillates at a frequency of 4, 194, 304MHz. It is obvious that this frequency is completely useless, as it is too big to be used as it is to our circuit. What we should is devide this frequency, in a way that in its final form, the pulse will have a frequency of 1Hz, which is the desirable frequency. Initially we use the integrated CD4060, which devides the imported frequency in its input, by forces of 2. As we can see on the integrated circuit the outputs are marked as Q4, Q5, G Qn. By importing a pulse in the CLK input of the 4060, with a frequency f Hz, we take out of output Qn, a signal which has a...

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