Electronic – Astable 555 Timer creates longer pulse when just turned on

555astablepulsetimer

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?

Best Answer

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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