Power cycle delay for HID lamps and motors

[sashimanu-san]

Some mains AC loads require a cool down period of several minutes after shutting down before powering on again, e.g. high intensity discharge lamps won't reignite, and a refrigerator unit may overheat.

Since the firmware has a software clock and NTP support, it is possible to cover some cases pretty easily:

• manual, remote or scheduled relay operation:
  • when real time is available —
    • just write the power off timestamp (ts) along with relay state to permanent memory, and don't power on until wall clock is ts+dt.
  • when no real time is available and the unit doesn't suddenly reboot in the meanwhile
  • count the seconds
  • unit reboots gracefully by user request
    • write a flag to permanent memory. Upon boot, read the flag and wait dt seconds if present, then power on the relay if needed.

A tough case is the following:

• recycling after a sudden unit reboot due to a power loss or other cause. Implementing this feature in software will require writing heartbeat to permanent memory every so often which may raise flash wear issues.

Any thoughts?

[xoseperez]

If the unit reboots due to a watchdog reset or a bug there is the chance to write to EEPROM before existing. If it reboots due to a power loss or hard disconnection there is no way unless what you suggest, which I wouldn't do.

[sashimanu-san]

I think I've found a solution for this case:

If the unit is restarting for reasons suspicious and time unknown and the stored relay state is ON then wait for the delay to expire however if the relay is commanded ON by a button press or network request during this period, power on immediately.