Learn how to implement an external watchdog timer using the popular 555 integrated circuit to prevent microcontroller hang-ups and latch-ups. Explore the circuit diagram, whiteboard explanations of the 555 timer functionality, and oscilloscope traces of the trigger mechanism. Follow along with a modified circuit layout in EasyEDA, get component sourcing tips, and see PCB layout examples. Gain insights into microcontroller failure modes and protection strategies, with references to technical resources on latch-up prevention. This comprehensive tutorial covers both theoretical concepts and practical implementation, making it valuable for electronics enthusiasts and embedded systems developers looking to improve the reliability of their microcontroller-based projects.