I'm trying to build a frequency measurement circuit using NE555P and Atmega328P. The circuit is the following : enter image description here

I use this library https://www.pjrc.com/teensy/td_libs_FreqCount.html

Always, The system works fine at the beginning (3 to 4 minutes) and then the frequency values start to drop until reaching 0.

Does anyone knows what causes this strange behaviour ? Thanks in advance.


1 Answer 1


It is very difficult to see, but as far as I can tell it looks like you have the wrong pinout for the 555 timer. The pins on the right-hand side should be numbered 5-8 from the bottom up, not from the top down:

enter image description here

If you have it connected the way the picture shows, I expect that's why it's giving you problems.

  • 2
    \$\begingroup\$ +1 for eagle eyes... I did not spot that. \$\endgroup\$
    – Trevor_G
    Mar 30, 2017 at 16:36

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