|Astable 555 Multivibrator|
|Above in Gadget form, Astable 555 Multivibrator Gadget , for your Webpage or Google Home Page.|
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
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Vary Ra, Rb and Ct with the controls given and see the change of frequency, period and duty cycle.