This is the circuit, before it was working, but not anymore. I have an identical circuit and its ulb still working. I don't know where is the problem.Circuit

(https://i.stack.imgur.com/fPpZW.jpg)enter image description hereenter image description here

  • \$\begingroup\$ Are you trying to place the lightbulb on the DC output or the AC Input? \$\endgroup\$
    – Jay
    Jun 2 '20 at 23:07
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    \$\begingroup\$ I think it would make sense then to put the bulb in parallel with the AC Input, before the Full Bridge Rectifier. \$\endgroup\$
    – Jay
    Jun 2 '20 at 23:11
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    \$\begingroup\$ You can have the bulb in parallel with the AC input, and have a switch before the bulb/rectifier. \$\endgroup\$
    – Michael
    Jun 2 '20 at 23:23
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    \$\begingroup\$ Can we assume that the bulb is not burned out? Also, the circuit can't work as shown. The bulb requires 50 mA to operate at the specified power level, but the 3.3k resistor is going to limit the current to no more than 7.3 mA through the LED (into a dead short). \$\endgroup\$
    – Dave Tweed
    Jun 3 '20 at 0:19
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    \$\begingroup\$ not working? what is the purpose of this circuit? \$\endgroup\$
    – Jasen
    Jun 3 '20 at 9:22

If you want to detect switch closure just take your exisiting circuit an connect the bulb in parallell with the bridge rectifier. enter image description here

  • \$\begingroup\$ Thank you, how? \$\endgroup\$
    – Shaydzmi
    Jun 3 '20 at 12:30
  • \$\begingroup\$ But I have the same circuit next to it, and it's working just fine. \$\endgroup\$
    – Shaydzmi
    Jun 3 '20 at 12:40
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    \$\begingroup\$ Hi Shaydzmi, According to your circuit, the lamp may glow only at the instant of grounding, as the 22μF capacitor charges up to 34V. That point onwards, the opto-coupler would give a continuous signal that grounding has occurred. In Jasen's circuit the lamp would also give a continuous indication of the grounding. \$\endgroup\$
    – vu2nan
    Jun 3 '20 at 14:54
  • \$\begingroup\$ @vu2nan, Thank you for the clarification. \$\endgroup\$
    – Shaydzmi
    Jun 3 '20 at 21:16
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    \$\begingroup\$ also, with the original circuit if the lamp fails the optcoupler will stop indicating activity. \$\endgroup\$
    – Jasen
    Jun 3 '20 at 22:23

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