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Electronic locks; advice on hardware and design

Discussion in 'General Electronics Discussion' started by yrreg, Sep 4, 2012.

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  1. yrreg


    Sep 4, 2012
    I'm fairly new to anything electronics related, so forgive me any stupid question I might ask. I'm a system engineer and programmer by day, I'd like to be an electronics enthusiast by night. ;)

    The thing I'd like to achieve is the following:
    I have 24 pairs of electronic locks, 48 in total. I would like to build a device to control them and read out their status over an ethernet network. The locks require a 12V DC power supply. In standby, the locks use 50mA max, when operating they use 200mA max. This is the wiring diagram for one lock, I think I understand pretty much what it says:
    Each lock draws power from the power supply and has two additional wires. One which can hold a switch to lock/unlock it and one that provides a signal to read the status.

    To unlock it, I need to supply 5V DC for a minimum of 50ms. To lock it again I need to open the contact or send 0V DC.
    To read the status, according to the manual it will be ON when it's open and LOW (GND) when closed.

    I would like to use one single power supply and one single "control device". I was thinking of using one Cat 5e cable for each pair and making 24 small splitter boxes to split each cable into 4 wires at the end. The locks would be somewhere between 1 and 18 to 20 meters away from the device.

    For the device, I was thinking along the lines of something like an Arduino but with an ethernet port, but I think someone will have a better idea? Basically, as long as it runs something I can program and provides access to status/switch in software I'm sure I'll get it to work.

    My questions:
    • Am I going to set the building on fire by using Cat 5e?
    • Which hardware should I get for the control device?
    • How do I wire everything together?

    Also, if you think this is too ambitious, don't be afraid to tell me. :)
  2. GreenGiant


    Feb 9, 2012
    you can do it with 1 arduino, and a mux (multiplex) system, and if you have access to/experience with labview you can set up a nice control on a computer screen that will monitor it nicely

    A friend of mine did something similar but only 6 switches and transmitted via a cell network (little more complicated but same idea)

    What you want to do is read the pins that go open/gnd through a mux, all on one (though it would be cheaper/easier to do with 2 X 16 pin mux's) then when one reads high figure out which pin it was on (based on which is active on the arduino) then at the end of the sweep send out a "report" via the ethernet connection to the PC, either to a decoder with LED's or to an email that a labview program reads

    Its going to be difficult but definitely doable, cat5 would be useable but you would only need... 4-5 of the strands to do pretty much everything you need to at each lock
  3. iknowvator


    Sep 5, 2012
    You can do it very easily by using RS485 bus. Not only it will be easy but cheap also. If you are ok with this let me know.
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    How are you powering the locks?

    They use 200 mA when "operating". Is this while they are locked? While they are unlocked? Or while they are changing from one to the other?

    So each lock needs a control signal, and provides a status signal. OK.

    This could be an issue. 20 metres is a long enough distance for voltage difference problems to occur, because of current flow in the wires, and earth voltage differences if the locks are powered from different power points. Ideally, each lock would have its own intelligent controller, and they would all communicate on a serial bus such as RS-485, as suggested by another contributor. RS-485 is a differential bus that uses two wires, so that common-mode voltages (within certain limits) do not affect the data. This would require a microcontroller at each lock (or each pair of locks), which is probably a lot more than you want. But there is still the issue of the cable lengths.
    I can't advise on this, sorry. I have no experience using micros with Ethernet.

    As long as you don't put much current through it, it won't get hot! But how are you planning to power all the locks?
    Are there Arduino boards available with Ethernet built in?
    Depends how you're going to communicate with the locks :-/
    Could be. Can you clarify the positioning and powering of the locks please. Also do you have microcontroller programming experience?
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