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This is a
very simple circuit utilising a 555 timer IC to generate square
wave of frequency that can be adjusted by a potentiometer.
With values
given the frequency can be adjusted from a few Hz to several Khz.
To get very low frequencies replace the 0.01uF capacitor with a
higher value.
The formula
to calculate the frequency is given by:
1/f = 0.69 *
C * ( R1 + 2*R2)
The duty cycle is given by:
% duty cycle
= 100*(R1+R2)/(R1+ 2*R2)
In order to
ensure a 50% (approx.) duty ratio, R1 should be very small when
compared to R2. But R1 should be no smaller than 1K.
A good choice would be, R1 in kilohms and R2 in megaohms. You can
then select C to fix the range of frequencies.
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