The IC 555 timer was invented by “Signetic Corporation” and it was termed as SE or NE555 timer. Generally, it is a monolithic timing circuit that gives precise and highly stable delays of time or oscillation. These types of ICs are very cheap and reliable in cost when we compared with the OP-Amp applications in the same areas. These ICs are used as an astable and monostable multivibrators in digital logic probes, DC-DC converters, tachometers, analog frequency meters, voltage regulators, temperature controlled and measurement devices. The IC SE555 is used for where the temperature ranges from – 55°C to 125°C and the IC NE555 is used for where the temperature ranges from 0° to 70°C.
What is a 555 Timer IC?
The IC 555 timer is a one type of chip used in different applications like an oscillator, pulse generation, timer. The designing of IC 555 timers can be done by using various electrical and electronic components like transistors, resistors, diodes and a flip flop. The operating range of this IC ranges from 4.5V -15V DC supply. The functional parts of the 555 timer IC include flip-flop, voltage divider and a comparator. The main function of this IC is to generate an accurate timing pulse. In the monostable mode, the delay of this IC is controlled by the external components like a resistor and capacitor. In the astable mode, both the duty cycle & frequency are controlled by two external resistors and one capacitor.
555 Timer IC Pin Configurations
The 555 timer IC consist of 8-pins where each pin has some function. The pin configuration of this IC is shown below.
Pin-1 is a GND pin which is used to supply a zero voltage to the IC.
Pin-2 is a trigger pin which is used to convert the FF from set to RST (reset). The output of the timer depends on the amplitude of the external trigger pulse that is applied to the trigger pin.
Pin-3 is an output pin.
Pin-4 is a RST pin. When the negative pulse is applied to this pin to disable or reset, and false triggering can be neglected by connecting to VCC.
Control Voltage Pin
Pin-5 is the control voltage pin used to control the pulse width of the output waveform and also the levels of threshold and trigger. When an external voltage is applied to this pin, then the output waveform will be modulated
Pin-6 is the threshold pin, when the voltage is applied to threshold pin, then it contrasts with a reference voltage. The set state of the FF can be depends on the amplitude of this pin.
Pin-7 is the discharge pin, when the output of the open collector discharges a capacitor between the intervals, then it toggles the output from high to low.
Pin-8 is the voltage supply pin which is used to supply the voltage to the IC with respect to the ground terminal.
Operating Modes of 555 Timer IC
The operating modes of a 555 timer are astable, bistable and monostable. Each mode of operation signifies with a circuit diagram and its output.
Astable Mode Operation
In this mode, the circuit of the IC 555 timer produces the continuous pulses with exact frequency based on the value of the two resistors and capacitors. Here the charging and discharging of the capacitors depends on a specific voltage. The circuit diagram of the 555 timer in astable mode is shown below. If the voltage is applied to the below circuit, the capacitors continuously gets charged through two resistors and generates pulses continuously. In the following circuit pins 2 & 6 are shorted together for endless re-activate the circuit. If the o/p trigger pulse is high, then capacitor in the circuit totally discharges. Long time delays are accomplished by using the higher values of the resistors and capacitors.
Monostable Mode Operation
In this mode, the circuit generates only single pulse when the timer gets an indication from i/p of the trigger button. Pulse duration can be depends on the values of the resistor and capacitor If an activating pulse is applied to the i/p of the circuit through a push button, then the capacitor gets charge and the timer circuit extends a high pulse, then it remains high until capacitor totally discharges. If it is necessary to enhance the time delay, then higher rate of capacitor and resistor are required.
Bistable Mode Operation
In this mode, the circuit produces 2-stable state signals which are low and states. The o/p signals of low and high state signals are controlled by reset & activate the i/p pins, not by the charging & discharging of capacitors. If a low logic signal is given to active pin, then the o/p of the IC circuit goes to high level. If the low logic signal is given to the RST pin, then the o/p of the circuit goes to low level.
Thus, this is all about 555 timer IC basics, pin description and operating modes. We hope that you have got a better understanding of this concept . Furthermore¸any queries regarding this concept or engineering project ideas, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the main function of a 555 timer IC?