I have a box which is used to put PCB in it when we are not using PCB. I want to turn on a UV blue LED for 1 minute when box is closed to cleanout the inside of box. I cant use limit switch as I don't have space for limit switch in my circuit. Issue with NE555 timer is if I use it in monostable mode then once box is closed the LDR connected to trigger pin 2 will trigger the output pin3 and LED will turn on but since box will be closed so trigger pin state wont change and LED will not glow for one minute. I also cant use MCU as I dont want any programming. I need suggestions for alternative solutions.

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    \$\begingroup\$ Is this a homework question? Either way, try showing a circuit diagram of what you have now, and then we can help you modify it to do what you want \$\endgroup\$
    – BeB00
    Aug 21, 2023 at 6:46
  • \$\begingroup\$ What's wrong with using and RC circuit with a large capacitor discharged across the UV LED? The brightness of the LED will dim over the course of the minute, but otherwise it will do the job. Depends on other limitations you have, as you apparenlty don't want to use an MCU either. \$\endgroup\$
    – Puffafish
    Aug 21, 2023 at 6:48
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    \$\begingroup\$ Does this answer your question? Blue UV LED Timer Circuit as this is the same question asked by you a few days ago \$\endgroup\$
    – Puffafish
    Aug 21, 2023 at 7:36

1 Answer 1



Any question with the NE555 tag can be answered with "use a microcontroller". This is also true for this question. It's the obvious choice, especially if you need low power when it's not in operation.

  • \$\begingroup\$ Actually I cant use any MCU aswell as I dont want to control it via a program. Dont we have any other solution for that? \$\endgroup\$ Aug 21, 2023 at 5:50
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    \$\begingroup\$ @ZunuranNasrullah If you have such limits you should update your question to include those. \$\endgroup\$
    – pipe
    Aug 21, 2023 at 5:52

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