Astable 555 Multivibrator - doc00019
This is a demo of the popular 555 timer. you can try out the
The Astable Configuration is like an Oscillator with a Square
wave output. You can adjust the Frequency and Duty Cycle (means
off time and on time pulse width as a %). The variation is done
by playing with the caps and resistors while looking in One Eye
at the Sacred Formula.
Do not overload the output pin or let high voltage/spike reach
any pin.. Do not reduce the the resistor to Pin 7 or Discharge
transistor, too much, it will burn out!
Press the Red button below to turn on the circuit press it again
to turn off. The 555 can source (LED2) or Sink (LED1) upto
It can even drive a small motor or lamp with diodes added to
protect from inductive kickback.
Vary Ra, Rb and Ct with the controls given and see the change of
frequency, period and duty cycle.
and images enabled.
Astable 555 Multivibrator xml
use iframe part for
your Webpage or Blog.
These are the formulae used by 555
T1 = 0.693 (Ra + Rb) * Ct
charge time of Ct
T2 = 0.693 (Rb * Ct)
discharge time of Ct
T = T1 + T 2
total period in seconds
F = 1 / T = 1.44 / ((Ra + (2 * Rb)) * Ct)
Frequency in Hertz
D = T 2 / T
duty cycle, multiply by 100 to get
Ct in farads and Ra-Rb in ohms.
The max power dissipation of 555 is 700mW so overload of more
than 200mA will damage the device, connecting the battery in the
reverse or wrong polarity will also damage device, ensure also
Ra and Rb do not go less than 2.2K (use 4.7K minimum) as it may
damage the discharge transistor at pin 7. The supply voltage can
go upto 18V. For CMOS 555 like 7555 see the datasheet they are
the above circuit in pdf format del00018.pdf
the cadsoft eagle source of the circuit del00018.zip
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