WELCOME To PROJECT CIRCUIT DESIGN

## Khamis, Julai 11, 2013

### Astable 555 Multivibrator

Astable 555 Multivibrator

 freq  Hz period Sec duty cycle
 Power Ra kilo ohms                                 mega ohms Rb kilo ohms                                 mega ohms Ct uF                                 nF
 LED1 LED2

These are the formulae used by 555 and same is used in javascript without any change.

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 different.
the above circuit in pdf format  del00018.pdf
the cadsoft eagle source of the circuit  del00018.zip

datasheet of LM555 here pdf.
pdf links may take time to load in the browser, save file target to your disk is better.
If LEDs are not lighting up, refresh the page. Tested in Mozilla 1, Opera 5 and IE5 with javascript and images enabled.

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 200mA. 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.

#### 3 ulasan:

1. It seems a very interesting project to work on. Well thanks for providing the diagram which makes the design work so easy.

Regards
Henry Jordan

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