Learn how to build and test an external watchdog timer circuit using a 555 timer IC to prevent microcontroller latch-ups and hang-ups. Explore the circuit diagram, PCB design process, and testing procedures using a signal generator and oscilloscope. Gain insights into PCB panelization techniques and discover how to power cycle Arduino or other microcontrollers automatically if they hang up. Access resources for components, including surface mount 555 chips and MOSFETs, and find links to additional information on the 555 timer IC and its applications in watchdog circuits.