I'm looking at building a watchdog that will power cycle my arduino (weather station) when it is not responding (my arduino gets a CMOS lockup and doesn't respond to reset).

I've read about designs with timers but haven't seen yet a simple design that would work with x hours at least. So was thinking of using a second arduino (to be replaced with ATTiny) and leverage interrupts + sleep mode so that if no ping is received from my main arduino, it will power cycle it. Was thinking of a circuit with NPN transistor. I suspect alot can be optimized there... any suggestions?

Initial watchdog circuit

  • \$\begingroup\$ no need for screenshot of the circuit diagram ... click "save and insert" when you finish designing the circuit \$\endgroup\$
    – jsotola
    Commented Apr 10, 2022 at 2:59

1 Answer 1


I do not understand what the diode is for? Not knowing what is connected to your Weather Pro Mini, opening the ground could cause some strange things to happen. Get rid of the diode and transistor and connect the grounds together. Put a P-Channel (logic level) in the VCC feed to the to the Weather micro. The Vgs must be less then 2.5V Source to VCC feed, Drain to VCC weather micro then connect the gate to D3, when the port is low the weather will be on. Use this to also power the peripherals, this guarantees they will also be reset.

  • \$\begingroup\$ Are you suggesting to replace the diode + BC337 with a P-Channel mosfet? Do you have any specific one to suggest? Sounds like this is exactly what I'm looking for. \$\endgroup\$
    – CadErik
    Commented Apr 10, 2022 at 1:56
  • \$\begingroup\$ Yes, I do not know your resources but you can google for them quite easily, They are available in SMD and Through hole. I have a similar design but I did it with discrete logic and switched the 12V. That guaranteed everything got reset. You can search for "P-channel high side switch" Most show a resistor. You can use that if you want but it will only be effective during watch dog reset. You have no inductive load so no diodes needed. When you select a MOSFET if you have a choice get an avalanche rated one, for future programs. \$\endgroup\$
    – Gil
    Commented Apr 10, 2022 at 2:16

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