Using two NE555 you can build this simple but useful generator. Very easy to understand how it works. The firs part is an astable configuraton, the second one, is a monostable configuration. This two "separated" circuits works now together. It is possible to change frequency by using a selector (in the circuit it is replaced by a deviator) to select different capacitance.
Hope it will be usefull.
Giuseppe Trainiti,
Italy, Sicily, Gela
