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Starting electronics
So, the frequency of the output signal of the circuit of Figure
5.2 is:
or, more correctly speaking:
Equation 1 is quite important really, because it shows that
the frequency of the signal is inversely proportional to the
capacitance. If we decrease the value of the capacitor we will
increase the frequency. We can test this by taking out the
10 µF capacitor and putting in a 1 µF capacitor. Now, the LED
flashes so quickly (about 58 times a second) that your eye
can’t even detect it is flashing and it appears to be always on.
If you replace the capacitor with one of a value of say 100 µF
the LED will flash only very slowly.
Now, let’s stop and think about what we’ve just done. Basically
we’ve used a capacitor in precisely the ways we looked
at last chapter — to charge and discharge with electrical
energy so that the voltage across the capacitor goes up and
down at the same time. True, in the experiments last chapter
you were the switch, whereas this chapter an IC has taken
your place. But the principle — charging and discharging a
capacitor — is the same.
The current which enters the capacitor to charge it, then
leaves the capacitor to discharge it, is direct current because
it comes from a 9 V d.c. battery. However, if we look at the
110