Why do you need an External Hardware WatchDog on an Arduino or Raspberry Pi?
The reason is the internal watchdog is disabled in the boot loader for the Arduino and the Raspberry Pi watchdog is unreliable and difficult to use. The SwitchDoc Labs Dual WatchDog Timer is designed to make small computer such as the Arduino and Raspberry Pi more reliable by detecting and recovering from computer or software malfunctions. It has two WatchDog Timers that can be used independently or together to reset non-responsive computers. It directly can drive the Arduino Reset line, the Raspberry Pi B/B+ and 2/3 reset line or a to a relay to reset a Raspberry Pi.
- You can download the Dual WatchDog Product Brief here (Version 2.02 as of December 12, 2016).
- You can download the Version 1 Dual WatchDog Product Brief here.
The SwitchDoc Labs Grove/Pin Dual WatchDog Timer is based on the 555 timer IC running in astable mode. The 555 timer acts as a “continuous” pulse generator. The pulse starts on power up or any time the trigger input is brought to ground. The setting of the TM1 potentiometer determines the length of the pulse (30-240 seconds). When the pulse ends the Arduino Reset output is taken to ground (and the PulseHigh output goes to VDD) for approximately 200ms. Then the cycle starts over again.