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ICs oscillators and filters
Ouch, that hertz
We can calculate the rate at which the LED flashes, more
accurately, from formulae relating to the 555. A quick study
of the square wave output shows that it consists of a higher
voltage for a time (which we can call T1) and a lower voltage
for a time (which we will call T2).
Now, T1 is given by:
and T2 is given by:
So, the time for the whole period of the square wave is:
and as the frequency of a waveform is the inverse of its period
we may calculate the waveform’s frequency as:
Earlier, we defined the two time constants, τ 1
and τ 2
, as
functions of the capacitor and the two resistors, and so by
substituting them into the above formula, we can calculate
the frequency as:
(1)
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