When making an astable circuit with a 555 timber, the frequency of pin 3s pulse is calculated using this: f = 1.44 / (R1 + 2R2) x C My question is why is 1.44 included.
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1\$\begingroup\$ We try to keep questions/answers clean and concise without additional "thanks" - if you like an answer you upvote it or accept it. The additional justification " ... for a project ... etc." adds nothing and should be removed. It's perfectly clean question w/o that. \$\endgroup\$– placeholderCommented Apr 30, 2013 at 21:06
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In the astable configuration, the low time is given by 0.693×R2×C and the high time is given by 0.693×(R1+R2)×C.
The factor of 0.693 is the scale factor (relative to the RC time constant) for the time that the capacitor takes to charge or discharge exponentially between 1/3 Vcc and 2/3 Vcc. The precise value is -ln(1/2) = 0.693147...
If you add the two half periods together, you get 0.693×(R1+2R2)×C for the total period.
If you take 1/period to get frequency, you can write it as 1/(0.693×(R1+2R2)×C), or you can move the constant to the top and write it as 1.442695/((R1+2R2)×C).
answered Apr 30, 2013 at 21:43