I am looking to set up a digital clock and wish to have a 1 Hz oscillator circuit. What is the best circuit? The Hartley or Collpits?
Neither. For a digital clock we need accurate 1 Hz pulses, because without accuracy the clock will advance or delay. The ideal solution for a clock or stopwatch oscillator requires the use of a crystal. What is usually done is to use a crystal of a certain frequency, higher than 1 Hz, because there is no crystal for this frequency and to calculate the number by which it must be divided to obtain 1 Hz. For example, if the crystal is 32 768 Hz, we divide it by this number to get 1 Hz. This is easy as 32 768 is power of 2 which makes it easy to use flip flops or counters like the 4020, 4040 0u 4060. The crystals are very stable the This is not the case with common oscillators whose frequency varies with temperature and the battery voltage itself. A very interesting solution adopted by designers is to buy a cheap digital wristwatch and locate in the circuit, using an oscilloscope, the point where you have the signal of your oscillator. This signal, accurate as it is determined by a crystal, can then be used as a reference for mounting. And if the circuit is powered by the power grid, you can use the frequency of 60 Hz (divide by 6 and 10) to get 1 Hz. This frequency is very accurate, as required by law.
