This is a very simple oscillator circuit that based on 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 figure of the circuit is following in below.
The operation of the circuit is follow by the formula to calculate the frequency that is given in below:
1/f = 0.69 x C x (R1 + 2*R2)
And 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 make with R1 in kilo ohms and R2 in mega ohms. You can then select C to fix the range of frequencies.
The operation of the circuit is follow by the formula to calculate the frequency that is given in below:
1/f = 0.69 x C x (R1 + 2*R2)
And 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 make with R1 in kilo ohms and R2 in mega ohms. You can then select C to fix the range of frequencies.
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