The IC 555 timer is monolithic timing circuit which can produce accurate and highly stable time delays and also the oscillation. This is available as an 8 pn IC that can operate temorature range between -50o to 120oC and the supply voltage ranges from +5V to +18V. The IC 555 timer can operate in two mode either (i) monostable (one shot) multivibrator or (ii) as an stable (free running) multivibrator . the IC 555 timer can use as a monostable multivibrator, astable multivibrator, analog to digital converter, digital to analog converter, waveform generators, analog frequency meter temprature measurement and control, voltage regulator and many other useful operation.