I want to control frequency and duty cycle of output pulse of 555 timer. I searched and find this schematic in a post in SOV but I don't know how calculate frequency and duty cycle in the circuit.


simulate this circuit – Schematic created using CircuitLab

What formulas should I use for calculating frequency and duty cycle? I would appreciate if you could kindly help me.


Any resistance in series with D1 will control the "high" time on the output, and any resistance in series with D2 will control the "low" time. By using two separate resistors, you can control each independently. Also, you could eliminate D2 entirely by connecting C1 (through a resistor) to Discharge.

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    \$\begingroup\$ If you eliminate D2 you remove the independence of duty cycle and frequency control. As it is, each pot controls only one of the variables. \$\endgroup\$ – Edgar Brown Dec 9 '18 at 17:33

be assure that ne555 has a lot of schematics version, but to calculate the frequency of the output pin, you can use this formula below.

the frequency formula is calculating by resistor in between of output pin.

enter image description here

RA = R5 ; RB = R6

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    \$\begingroup\$ And how do you find the duty cycle? \$\endgroup\$ – JRE Sep 13 '17 at 9:46

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