For those of you who run servers that need to be run 24/7, PC fans failures can cause component damage that could be costly. But there’s a simple PC fan failure alarm circuit you can use to alert you when your PC fans fail, subject of this blog post.
Many different design ideas came to my mind and i tested a couple of them. Some did work, some others failed. The most reliable and yet simple design was to convert the output of the fan tacho into voltage and compare it with a comparator or Schmitt trigger
Also, don’t forget to check out my alarm system DIY as reference.