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474 posts

Ultimate Geek
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Topic # 223296 22-Sep-2017 16:56
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Another one of those what the heck is the correct term for this as my google foo has failed again.


I'm currently looking at setting up electronic door locking system the the common door lock types are Fail Safe(Most Common)/Fail Secure however what I'm wanting is something in between


The idea being that if the UPS starts feeding from the battery it tells a Raspberry Pi, the Raspberry Pi then checks its calendar and then programmatically set the lock to lock if it's a defined Fail Secure time or unlocked if in a Fail Safe time so that if the power outage lasts longer than the UPS can supply it keeps that state however none of the locks I can find do this and googling terms that make sense for this type of configuration returns nothing of use.


I guess I could take one of the Fail Safe door bolts and remove the cap that must power it during a outage or unlocking but that feels like a lot of work and may cause some other issues. surely I cannot be the only one who needs this type of lock. 



Geoff E

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263 posts

Ultimate Geek
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  Reply # 1871151 22-Sep-2017 17:21
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Are you using one of those magnet plates or a latch?


Main issue you will find, is that the common "Fail open" is that when the electo-magnet looses power it will naturally stop "grabbing" the door. 




What you are describing, is a magnet that can have its magnetic properties changed based on an input?

474 posts

Ultimate Geek
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  Reply # 1871156 22-Sep-2017 17:37
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Something more like this sort of lock (


Given that they also say they fail safe there has to be some mechanism or to push the bolt back up when unpowered looking at it. Not really sure how it does this. Was originally thinking that it used a motor to turn the shaft but that one above says its a solenoid so now not sure it would be a cap powering it to change into a fail safe method.

Geoff E


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  Reply # 1871162 22-Sep-2017 17:49
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electric deadbolts tend to have one wire for lock, one for unlock and a ground when I looked at them, and would hold state since they just moved when powered.


474 posts

Ultimate Geek
+1 received by user: 101


  Reply # 1871167 22-Sep-2017 18:25
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electric deadbolts tend to have one wire for lock, one for unlock and a ground when I looked at them, and would hold state since they just moved when powered.



Do you remember where it was you had seen them. Not having much luck my self. Most of the ones I can find are either the solenoid type or have really no/poor documentation. Have found no 3 wire interfacing ones either. Looks almost like the sellers are picking the 2 wire ones I'm guessing this is so they can buy controllers in bulk while allowing for a bigger range of lock mechanisms.

Geoff E

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  Reply # 1871222 22-Sep-2017 21:23
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It sounds like you want the equivalent of a car central locking system. In that it only needs power to change state. Note that this can easily be achieved with only 2 wires coming out of the lock unit. Imagine those wires are labelled A and B. At rest both wires are either connected to ground or are not connected to anything. To lock - connect A to positive and B to negative. To unlock connect A to negative and B to positive. This circuit is easy to wire up using 2x double throw relays. It then becomes - switch on relay 1 to lock, or switch on relay 2 to unlock.


And then you need a detector circuit to check that the door is closed before you try to lock it. And it is always useful as well to have outputs that indicate whether the door is currently locked, unlocked or open. So you can remotely lock the door and get a confirmation back that the door is successfully locked. And if the door fails to lock you then get an error or warning that it failed to lock.


Im following this thread with interest. As I have an electronic lock system on my own door that I made myself - As I wanted pretty much exactly what @geocom wants, But I couldn't find anything readily available. As basicly everything that is either fail safe or fail secure, has a default state that doesn't draw power. But then draws power continuously if you want the lock to stay in the non default state. (The big electromagnet type is the best example of this).


My system is a solenoid that I welded onto a metal rod that in turn is part of a homemade latch. It is mostly reliable considering that it is a home brew design. But it makes a really loud clunk when the door unlocks and again when the door closes. And it looks ugly as sin. But it's main advantage is that it draws virtually no power while at rest. Only resting power is used by the RFID reader, so it was far easier to make a UPS for it. My system is crying out to be upgraded and integrated with a home automation system. Those loud clunks are annoying.

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