Square wave generator using 555 timer

This electronic project is a piece of test equipment designed using a 555 timer circuit. It's a square wave generator with 6 selectable frequencies from 1Hz to 100kHz, incrementing in decade values .
This square wave generator electronic project is based on the popular 555 timer IC and generates six preset frequencies from 1Hz to 100khz. It has a wide operating voltage range and even provides visual indication of the output.

This square wave generator project is most useful as a Signal Injector for radios and TV's. A square wave is the most suitable for testing the IF (Intermediate Frequency) strip as the signal will pass through the IF transformers without any attenuation, no matter what the tuned frequency of the circuit .
The 555timer is configured for astable operation, meaning that it will trigger itself and free run as a multivibrator.
The timing elements are resistors R1, R2 and one of the capacitors (C1-6).
For the values shown in this diagram , the six frequencies generated are 1Hz, 10Hz, 100Hz, 1khz, 10khz and 100khz.
If you want to generate a variable frequency you can replace the 68k resistor with a 100k mini trim pot , connected in series with a 10 k resistor . This square wave oscillator electronic project can be powered from a power supply that can provide an output voltage between 5 and 18 volts DC , but typically it’s recommended to use a 9 volt DC power supply .