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Topic: single coil bistable / latching relay (Read 12297 times) previous topic - next topic


I have designed it this way so that I can still switch the white LED strip on and off using the wall switch even if the Arduino has failed for some reason.
Again, I find that a rather inappropriate design consideration.  Whatever makes you think the Arduino will "fail"?

There is some small possibility the program could crash, generally from impulse interference from the power circuitry that you are controlling.  That is why you have a watchdog timer available to restart it in such circumstances, so that is adequately provided for.

The power supply to the Arduino could fail.  It might be a consideration then to fail with the lights on using normally closed contacts on the relay if the illumination is important.  Again, using the EEPROM to remember the last determined state will mean that the lights will not spuriously switch on merely due to a power outage.  On the other hand, the power supply to your 12 V LEDs is equally likely to fail, so you get no light anyway.

The simplicity of using a single, ordinary relay should outweigh any advantage of using a latching relay in a "two-way" configuration with the wall switch.

And I recently had to replace the wall switch to my daughter's en-suite light.  It broke from years of use - I hardly need to explain why.


I'm afraid we have to agree to disagree on this one. The fail safe was a requirement by 3 wives (mine and those of 2 other friends who use the same system in their house; not all 3 my wives :D ). They don't want to do their make-up in the dark when (not if!) "our stuff" fails. ;-)
And it is not completely unheard of that an Arduino fails.

Also, a normal relay draws a current to stay on, a bistable one doesn't and therefore helps a bit to save some energy (minimal, I know, but it adds up throughout the house).

Location: Berkshire, UK
My Astro and DIY projects website: http://yesyes.info/

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