do i need a relay?

by manshuk89
Tags: None
manshuk89 is offline
Jan7-10, 10:46 AM
P: 7
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?
Phys.Org News Partner Engineering news on
Lifting the brakes on fuel efficiency
PsiKick's batteryless sensors poised for coming 'Internet of things'
Researcher launches successful tech start-up to help the blind
Bob S
Bob S is offline
Jan7-10, 11:05 AM
P: 4,664
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
sophiecentaur is online now
Jan7-10, 11:44 AM
Sci Advisor
PF Gold
sophiecentaur's Avatar
P: 11,358
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.

manshuk89 is offline
Jan8-10, 11:32 AM
P: 7

do i need a relay?

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?

Register to reply

Related Discussions
step relay????? Electrical Engineering 4
help me in relay Electrical Engineering 5
Relay Chattering Electrical Engineering 4
110V relay help Electrical Engineering 8
relay and its application Electrical Engineering 3