Redundant Outputs

[chopperwalker]

I haven't found this in the forum so I have to ask. I have two different microcontrollers that I want to control one relay with. It's a redundant system and (ideally) they won't operate at the same time. One is a 20x2 the other is a Picaso (uLCD-32PT) from 4D labs. The picaxe operates as a manual control of system in a panel. The picaso touchscreen is an automated system controller. The purposed of the setup is to allow manual operation until the touchscreen controller is totally debugged and in case the touchscreen is ever damaged (operating in a hot, wet environment with drunk people).

I need both to operate a reed relay. Do I need diodes to protect from the opposing outputs? What's the safest way to set this up?

Thanks in advance

 

[eclectic]

Sounds a bit (lot) Safety Critical.

Some more detail might be in order.

e

 

[hippy]

I need both to operate a reed relay. Do I need diodes to protect from the opposing outputs? What's the safest way to set this up?

Simple diode mixing is one way though there are a number of ways to do it; a logic OR gate, two opto's or two relays in parallel. I'd recommend something to keep the two outputs immune from each other and then it's a question of how separated they are. The case against simple diode mixing or logic gate is both require a common 0V and that may introduce issues.

 

[Buzby]

I concur with hippy. Two optocouplers and/or two relays, keeps any 0v problems at bay.

 

[chopperwalker]

It's not that safety critical. I am more worried about the equipment than the safety of people. Not that I am heartless, the setup just doesn't pose as much a risk to the people as they do to it.

I think I will try two reed relays in parallel. I have another on hand. Thanks guys.

 

[chopperwalker]

I went with two reed relays in parallel. It seemed to run fine with either setup. No smoke and everything works still Thanks!