# Automatically Repeating Interval-Timer Circuit

Posted on Feb 6, 2014

The Cmos 4060 IC has two built-in inverters - at pins 9, 10 and 11. They must be wired together to form an oscillator - the output of which is at Pin 9. While the oscillator is running - Pin 9 is switching continuously from high to low and vice-versa. It`s rather like the swing of a pendulum - or the ticking of a clock. The speed at which the osci

llator ticks is controlled by R6, R7 & C4. = Note that R6, R7 & C4 are connected in series between the outputs of the two inverters. If the cycle starts with Pin 11 low - then Pin 10 will be high - and Pin 9 will be low. So the capacitor will begin to charge from Pin 10 - through R6 & R7. The speed at which it charges depends on the value of the capacitor - and the setting of R7. As the capacitor charges - the voltage at the junction of C4 & R7 will rise. When it reaches just over half the supply voltage - it takes Pin 11 high - through R8. = Now everything reverses. Pin 11 is high - so Pin 10 is low - and Pin 9 is high. C4 begins to charge again - only this time it`s in the opposite direction. As Pin 9 charges the capacitor - the voltage at the junction of C4 & R7 will fall. The speed at which it falls depends on the value of the capacitor - and the setting of R7. When it falls to just below half the supply voltage - it takes Pin 11 low - through R8. With Pin 11 low the cycle is complete - and the next cycle can begin. = The oscillator runs because the polarity of the charge on C4 keeps reversing. As a result - the junction of C4 & R7 keeps taking Pin 11 back and forth between high and low. And since Pin 11 keeps changing back and forth between high and low - the polarity of the charge on C4 keeps reversing. It`s a sort of controlled feedback - where the frequency generated is determined by the values of R6, R7 & C4. = The...

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