I was trying to make a monostable timer for a specific project which should trigger output high for around 5 seconds. For that, I have chosen a capacitor of 4700uf and a resistor of 1K.

According to the formula of monostable mode (\$T = 1.1 * 1000 * 4700\$), it was supposed to trigger a pulse width of about 5 seconds, but when I built it the timer pulse width is something more than 5 seconds, around 10-15 seconds

Here is my schematic:


simulate this circuit – Schematic created using CircuitLab

What mistake did I make here? Please point out the mistake with valid schematic if there is any.

  • \$\begingroup\$ Have you tried other capacitors and resistors to check if they give the correct timing? \$\endgroup\$
    – HandyHowie
    Mar 3, 2021 at 7:43
  • \$\begingroup\$ Check if the component values are correct. Try different capacitor-resistor pairs (e.g. 22k - 220u, 47k-100u, etc.). \$\endgroup\$ Mar 3, 2021 at 7:47
  • \$\begingroup\$ @HandyHowie i tried 1k resistor with 1000uf capacitor which was supposed to have a pulse width of 1 sec but actually had almost 5 sec, same problem just i mentioned above. \$\endgroup\$ Mar 3, 2021 at 8:11
  • \$\begingroup\$ @Rohat i will let you know after giving it a try. \$\endgroup\$ Mar 3, 2021 at 8:11
  • \$\begingroup\$ Are you sure you are reading the resistor colour codes correctly? \$\endgroup\$
    – HandyHowie
    Mar 3, 2021 at 8:35

1 Answer 1


Sorry for wasting your time guys, after a close inspection, i found the IC faulty, when replaced with another one, it works fine, Actually, i couldn't even think that a newly bought IC can turn out to be a faulty one ...

  • 1
    \$\begingroup\$ That's good. You can accept your own answer do that the question topic does not remain open. \$\endgroup\$ Mar 3, 2021 at 10:18
  • \$\begingroup\$ Subha Jeet Sikdar - As kindly commented by Rohat, you can accept your own answer but only 48 hours (or more) after you asked the original question (see here). So please come back and accept it after that delay. Thanks! \$\endgroup\$
    – SamGibson
    Mar 3, 2021 at 12:42

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