Q.Draw the block diagram of 555 timer.

A non-sinusoidal (relaxation) oscillator produces a repeating output that is not a sine wave — a square, rectangular, triangular or saw-tooth waveform. Unlike a sinusoidal oscillator, it does not rely on a resonant frequency-selective network; instead it uses the repeated charging and discharging of a capacitor, switched by a device that abruptly changes state. The standard building block is the 555 timer IC.

The 555 is a low-cost, reliable monolithic timing IC available as an 8-pin package. Its functional block diagram contains four parts: three equal $5\,\text{k}\Omega$ resistors forming a voltage divider across the supply (fixing reference voltages of $\tfrac{1}{3}V_{cc}$ and $\tfrac{2}{3}V_{cc}$); two comparators; an RS flip-flop; and a discharge (npn) transistor. Comparator 1 compares the threshold (pin 6) with $\tfrac{2}{3}V_{cc}$ and sets the flip-flop; comparator 2 compares the trigger (pin 2) with $\tfrac{1}{3}V_{cc}$ and resets it. The flip-flop output drives the output pin (pin 3) and controls the discharge transistor (pin 7). The eight pins are Ground, Trigger, Output, Reset, Control voltage, Threshold, Discharge and $+V_{cc}$ (which may be $+5\,\text{V}$ to $+ …