Do i need a relay?

  1. i have just purchased a digital lock that works on 12v dc...
    the lock has a transformer and a rectifier , hence i connect it directly to the mains....
    when i switch the button on, the lock opens...

    now i want to connect a keypad to this digital lock such that it opens only when a correct code is entered......
    my question do i need a relay to operate this mechanism..? if yes then why?
     
  2. jcsd
  3. If the keypad runs on 12V dc (regulated), then you could use an npn open collector (common ground) to operate the lock. A relay does provide an extra layer of isolation, however, in case the lock solenoid requires a lot of inductive current.
    Bob S
     
  4. sophiecentaur

    sophiecentaur 13,280
    Science Advisor
    Gold Member

    A relay is an old fashioned device which does a lot for you. It provides very good isolation (it can switch AC, for example) and, effectively, very high signal amplification. You may need a diode and capacitor to deal with switching spikes with an inductive load but that is not a problem. The only thing wrong with relays is reliability, because they have moving parts (and, of course, they are non-linear). Nonetheless, they are a very effective low-cost way to achieve just what you seem to want. Reliability is not really an issue.
     
  5. thanks a lot for the reply guys.....
    i have successfully made a password protected lock using a relay........ i think i will add the diode for protection against spike just in case....

    i am now thinking about takin this module to the next step.....
    i want the password to change every 2 days and a notification 2 be sent via an sms to the mobile phones of some predetermined individuals.....

    i know a few mechanisms of password generation....
    can anyone tip me as how to incorporate a gsm device for the sms purpose?
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook