555 IC Timer Monostable and Astable Design Calculator

Instrumentation and Electrical Design

555 IC Timer Monostable and Astable Design Calculator.

The 555 timer IC integrated circuit is the first and still one of the most popular IC timer chips in use. This timer IC operates as a one-shot timer or as n astable multivibrator. The 556 IC is a two 55 circuit chip.

555 ic pinout

The connection of the pins for a DIP package is as follows:

Pin Name Purpose
Pin Designation Description
1 GND Ground reference voltage, low level (0 V)
2 TRIG The OUT pin goes high and a timing interval starts when this input falls below 1/2 of CTRL voltage (hence TRIG is typically 1/3 V CC , CTRL being 2/3 V CC by default, if CTRL is left open).
3 OUT This output is driven to approximately 1.7 V below + V CC or GND.
4 RESET A timing interval may be reset by driving this input to GND, but the timing does not begin again until RESET rises above approximately 0.7 volts. Overrides TRIG which overrides THR.
5 CTRL Provides "control" access to the internal voltage divider (by default, 2/3 V CC ).
6 THR The timing (OUT high) interval ends when the voltage at THR is greater than that at CTRL (2/3 V CC if CTRL is open).
7 DIS Open collector output which may discharge a capacitor between intervals. In phase with output.
8 V CC Positive supply voltage, which is usually between 3 and 15 V depending on the variation.

Pin 5 is also sometimes called the CONTROL VOLTAGE pin. By applying a voltage to the CONTROL VOLTAGE input one can alter the timing characteristics of the device. In most applications, the CONTROL VOLTAGE input is not used. It is usual to connect a 10 nF capacitor between pin 5 and 0 V to prevent interference. The CONTROL VOLTAGE input can be used to build an astable multivibrator with a frequency modulated output.

555 IC Timer Monostable

555 IC Timer Astable


555 Timer Calculator  
RA Ohms  
RA Tolerance %  
Capacitance Digits  
C Tolerance %  
Period = 1.1 x R x C    
Period = seconds  
Period = ms  
Min Period = seconds  
Min Period = ms  
Max Period = seconds  
Max Period = ms  
555 Timer Astable Calculator  
RA Ohms  
RA Tolerance %  
RB Ohms  
RB Tolerance %  
Capacitance Digits  
C Tolerance %  
Time High = 0.693(RA + RB) x C  
Time High = seconds  
Time High = ms  
Min Time High = seconds  
Min Time High = ms  
Max Time High = seconds  
Max Time High = ms  
Time Low = 0.693 x RB x C  
Time Low = seconds  
Time Low = ms  
Min Time Low = seconds  
Min Time Low = ms  
Max TimeLow = seconds  
Max TimeLow = ms