Design an IC 555-based symmetrical square wave generator for $1 \mathrm{KHz}$ frequency of $\mathrm{Vcc}=5 \mathrm{~V}$, Draw waveforms for voltage across timing capacitor and output.

Solution:

The circuit used for the square wave generator is shown in fig (a). For a square wave, charging and discharging resistors must be equal.

The resistance $R_1$ is a combination of a fixed resistor and a potentiometer -so that potentiometer can be adjusted for the exact square wave.

$ \begin{aligned} f &=1 \mathrm{KH}_2 \\\\ T &=\frac{1}{f}=1 \times 10^{-3} \mathrm{~S} \\ T_d &=\text { discharge }=\frac{T}{2}=0.5 \mathrm{msec} \end{aligned}\\ $

$ T d=0.69 R_2 c\\ $

choose, $C=0.1 \mu \mathrm{F}$

$ \begin{aligned} 0.5 \mathrm{msec} &=0.09 R_2 \times 0.1 \mathrm{NF} \\\\ 0.5 \times 10^{-3} &=0.69 R_2 \times 0.1 \times 10^{-6}\\ \\ R_2 &=7.25 \mathrm{k} \Omega \end{aligned}\\ $

For a square wave, $R_1=R_2$

$ \therefore \quad R_1=100 \Omega+10 \mathrm{~K} \Omega \text { pot } $

The output voltage and capacitor ut $\quad T_c=T_d=0.5 \mathrm{msec}$