What is Timer 555 IC ?
Timer 555 generates periodic waveforms. An external R and C network sets the period and duty cycle. It is not designed to be a harmonic oscillator. It can be found in the market as NE555, LM555, etc.
Application example
A turn indicator in a vehicle requires a timer to decide the on-off frequency. So, timer 555 can be used to provide the control signal. If, in an application, the frequency requirement is not more than 1MHz, then this timer IC could be a good solution. The output of this IC can assume only two voltage levels, i.e., AVDD and AVSS.
Timer 555 block diagram
Modes of operation
Depending on the application requirement, Timer 555 can be configured into one of the following modes by modifying the circuit connection.
Astable multivibrator
It means that output is not stable at any of the two voltage levels. If the output goes to AVDD then it won’t stay at AVDD for longer than Tperiod/2. It will go to AVSS and there also it won’t stay for more than Tperiod/2. So, it behaves as an oscillator with the time period of Tperiod in astable mode. It is the most common use.
Bistable (Flip-flop circuit)
It is stable at both of the output voltage levels. So, it requires some input that can force it to any of the required logic voltage levels, similar to the SR latch circuit.
Monostable
Schmitt trigger
