Remote and local control panels for an irrigation controller

[e100]

Has anyone done any projects where there was a need for two control panels, one back at base, the other out in the field?

If you are in the field then you need to be able to take local control locking out the base control panel until you've finished what you are doing.
Likewise if you return to base and forgot to relinquish field control then you need a way of forcibly resuming base control.

I realise that for this to make sense to the operator both panels would need to use stateless hardware controls, so switches would have to be momentary and rotary encoders would be needed to change numeric values.

Whichever panel is in charge would need to broadcast a flag saying that's it's in control and also listen for the same signal from the other control panel incase it wanted to take over. (The intention is to link everything together with CAN bus so messages rather than hardware i/o lines will be used for communication.)

It sounds like a deceptively simple thing to implement but not having done this before I'm not so sure. Are there any gotchas that I should be aware of?

[woody]

I would not let the control panels themselves decide or check who is in control. Let the central system do that.

Keep the settings central. Let a control panel know its state, either in control or not in control. Indicate with an led. Whenever a switch is pressed or a rotary encoder is turned while a panel is not in control, request control from the central system. Then retrieve the settings and present them on the control panel. Dial in the required settings and store them centrally.

If you don't want the hassle of reading buttons and checking control all the time you could also make a separate 'take control' button on the control panels. And if you make that an RFID card reader that also solves the collision problem; only the one with the card can take control. Although this introduces another problem when the card goes missing :-)

Interesting challenge. I once made a gate controller with a couple of wirelessly attached card readers that also were used to program cards, and it is as you said: deceptively simple.