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Eager to put my new Geiger-Müller tube to the test, I embarked on the journey of crafting a custom circuit for the purpose.

This is my circuit:

enter image description here

Getting straight to the point, my circuit successfully operated after a few tests. The unfortunate twist is that the astable multivibrator NE555 timer unexpectedly stopped functioning after a few uses, leaving me puzzled about the cause. I'm reaching out for your assistance to understand why it broke suddenly and seek guidance on how to fix the issue.

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  • \$\begingroup\$ No decoupling capacitor. No butee resistor with the pot at discharge pin ... No limiting resistor wired serial with 100 mH ... \$\endgroup\$
    – Antonio51
    Commented Dec 9, 2023 at 18:39
  • \$\begingroup\$ Are you sure it is the 555 and not the npn? \$\endgroup\$ Commented Dec 9, 2023 at 18:59
  • \$\begingroup\$ Where should I put the decoupling capacitor? and what is a butee resistor? @Antonio51 \$\endgroup\$
    – Doobalo
    Commented Dec 9, 2023 at 19:05
  • \$\begingroup\$ The NPN transistor works. @StainlessSteelRat \$\endgroup\$
    – Doobalo
    Commented Dec 9, 2023 at 19:07
  • \$\begingroup\$ @Doobalo when the pot is to zero (high position), you must limit the current from the power supply ... so insert a resistor to do that (1 kOhm would do). \$\endgroup\$
    – Antonio51
    Commented Dec 9, 2023 at 19:18

1 Answer 1

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For best explaining the 1 kOhm position ... I made this circuit.
You can see what happens when the cursor of the pot is "high".
As showed, the current through R13 is very "high", like 0.8 A ...
This is bad for the 555.

enter image description here

You should add also a "decoupling" R-C (in green) at supply of MOSFET ...

enter image description here

Note also that your circuit lacks a "regulation" system for the voltage output.

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  • \$\begingroup\$ I truly appreciate your assistance! Planning to test this tomorrow since it's quite late in my timezone. I might return if I encounter any hiccups and or do something stupid :) \$\endgroup\$
    – Doobalo
    Commented Dec 9, 2023 at 21:39
  • \$\begingroup\$ Tested it today and it seems more happy :) Thank you. Lets see if it lasts. \$\endgroup\$
    – Doobalo
    Commented Dec 10, 2023 at 9:14

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