The 555 Astable oscillator gives a square wave output at pin 3, The output drives two LEDs, LED1 lights up when pin 3 is low and LED2 when pin 3 is high.
Astable 555 Timer Flasher
The 555 can source (LED2) or Sink (LED1) upto 200mA. It can even drive a small motor or lamp with diodes added to protect from inductive kickback. Vary Ra, Rb and Ct and see the change of frequency, period and duty cycle.
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 different.
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.
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.
This is a tutorial with calculator to help learn the application of 555 which is a very rare chip innovation. It is simple, versatile, flexible and programmable (by tweaking of pots).