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I have a question regarding the behavior of a 555 timer circuit that I have made. It is depicted below.

enter image description here

Now, here is some interesting behavior, I wrote a program on arduino that measures the lengths of the pulses from this 555 timer. Here is the output that I had.

  Was on for: 472
  Was on for: 279
  Was on for: 279
  Was on for: 277
  Was on for: 278
  Was on for: 278
  Was on for: 278
  Was on for: 279
  Was on for: 277
  Was on for: 278
  Was on for: 278
  Was on for: 277

Now, as you can see, when the 555 timer is first turned on, the pulse is much longer (measured in milliseconds). My question is, how would I avoid this behavior? In other words, how can I turn an astable 555 timer on and off and have the first pulse be the same length as all of the other ones?

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  • \$\begingroup\$ Does anyone else feel that on calculation last pulse deviates just too much from actual answer that is around 303ms. And value of control capacitor is too high. \$\endgroup\$ – manav.tix Jan 1 '16 at 8:09
  • \$\begingroup\$ @manav.tix, that last pulse is an anomaly because I turned off the circuit, I will remove from the question since it is confusing. \$\endgroup\$ – Anthony Dito Jan 1 '16 at 8:10
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Add a 4.7uF capacitor from pin2 (top end of 10uF) to vcc reduce the timing resistors by one third.

this way the capacitor pair will power up as about 1/3 VCC and the pulses will go from there all coming out at about the same size,

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  • \$\begingroup\$ Thanks for the help! I just threw in another 10uF capacitor into the circuit where you said (I don't have a 4.7uF capacitor around) without changing the resistors and I am getting pulses of the same length. Great answer. \$\endgroup\$ – Anthony Dito Jan 1 '16 at 8:40

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