In the present article, we will describe the function of a digital stopwatch, 0 – 99 sec. The function of the stopwatch, relies in the use of 4 integrated
circuits, which in this case belong to National Semiconductor.
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 crystal’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.
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,… 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 frequency equal to f/2n,. So, by exporting the signal out of Q14, knowing that the imported