odd divider

It is often necessary to divide the frequency of some signal by a given factor. For example, several signals may be required with frequencies that are all some fraction of a main "clock" signal. In this kind of situation, special-purpose "d iv ider" ICs may be used, but these have the disadvantage that they can only divide by multiples of two — even numbers, in other words. When an odd division ratio is required, some other system must be used. One of the most common is to use a "counter" IC: this is reset each time it reaches the count that corresponds to the desired division ratio (three, say). This system has a disadvantage: the output signal is asymmetric, with a duty-cycle that depends on the division ratio. The circuit described here gives a square-wave output with a 50% duty- cycle (provided the input signal is also symmetrical), and can be set to divide by any odd number between 3 and 29. The basic principle is both simple and ingenious — like all good inventions. A co...