Simple Variable Frequency by 555

Here 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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