Square wave generation using 555 timer IC need extra circuit arrangement in astable multivibrator. For Square wave generation duty cycle should be 50% and with the help of 555 timer IC. So a diode connected parallel with the R2 resistor. At charging time resistance R1, diode and capacitor come in the picture and discharge through diode D2, resistance R2 via discharging pin number 7 of 555 timer IC. By adjusting the values of resistors R1 and R2, a working cycle can be found between 5% and 95%, plus the square wave output. The square wave generation circuit is shown below.
To obtain a square wave, the duty cycle can be set to 50% by standardizing the values R1 and R2. The square wave generation waveforms are shown below.
A duty cycle of less than 50% is achieved when the resistor R1 is lower than the resistor R2. In general this can be achieved with potters with R1 and R2. Another circuit of a square wave generator can be removed from the removable multi-oxides without the use of diodes. Add the resistor R2 between pins 3 and 2, the output connection and the trip terminal. The circuit is shown below
In this circuit, the charging and discharging processes are only carried out via the resistor R2. The resistor R1 must be high enough not to break the capacitor during cutting. It is also used to ensure that the capacitor takes up the upper limit (VRT).