Relay output off on comms timeout?

[lassenie]

I wonder what would happen for a Relay Actuator (as shown among the examples) if the communication with the controller is lost. Then the outputs may be active forever.

So, I believe an actuator like this should not be trusted to activate anything critical (heaters, pumps etc.) unless I add functionality to turn off the output in case of communication timeout. I guess I can not count on existing controllers to keep sending regular updates to the output state, so I don't know how I could even detect communcation timeout. What do you recommend?

[mfalkvidd]

@lassenie I agree. If the relay is controlling something critical the node should have as much as possible of:

• Turn relay off if power is lost (relay should default to shut off if it has no signal/power)
• Default relay to off when starting after power loss / reset
• Use watchdog to reset the node if the sketch hangs
• Use a timer to turn relay off after some appropriate interval if no signal is received from the controller
• Add a hardware watchdog, like discussed here

[lassenie]

@mfalkvidd Thank you for your valuable suggestions - they all look very relevant.

Perhaps I am overlooking something in the documentation, but I wonder if any existing controllers out there will get the node's relay outputs in the right state again after a node restart, if it always starts up in off state.

Besides that, how can I reliably detect communication in the node, such as I_HEARTBEAT/I_HEARTBEAT_RESPONSE? As far as I know, such internal messages do not arrive through the recieve(...) API function. I will need to see some incoming messages (also from existing controller implementations) - otherwise I would get timeouts.

Best regards
Lasse