555 timer tester

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This is a very useful little circuit. When I first worked with 555s they were dying constantly, which becomes very annoying. This nifty little circuit will quickly tell you whether or not a 555 is functioning which is great for troubleshooting 555 related circuits. The LED will flash quickly if the 555 is functional. If anything else happens the timer is dead.



The frequency is set to about 1 Hz. By using a 555 timer calculator it can be adjusted easily. The maximum frequency is 300 - 500 kHz.



  • Make sure everything is wired correctly.
  • Check LED and capacitor polarity. 
  • Make sure there is 9V at pin 8 and 4, and 0V at pin 1.
  • Make sure your test timer isn’t dead.


Pictures of tester

As you see I’ve built my tester ontop of a buttoncell battery holder. This reduces size and leaves everything in a nice easy access package.

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