Replacing normal relays with self lock relays

Discussion in 'General Electronics Chat' started by Hali, Feb 26, 2007.

  1. Hali

    Thread Starter New Member

    Feb 26, 2007
    Hi all

    I'm designing a circuit for a system that takes I/P frm the user through a button...button s scanned by ucontroller...Then it has to switch ON/OFF an outer system that is operating on 28VDC. The properties of the ON/OF signal are

    1. ground for switching ON & Open for switching OFF the system(Confusing)

    Controller energizes the relay to generate this signal.

    2. The relays should b working in such a way that if the power fails,the state of the signal that is going to the outer sytem should not change....

    The problem is what kind of relays I should be using....and how to meet the two conditions
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    The button sensing and the relay controlling are separate issues. If the on/off button is correctly sensed as things are now, then that issue is not significant.

    Replacing the relay now being used with a latching type should be possible. Finding one with a compatible coil voltage and current capacity is enough as far as the hardware requirement goes. Consider changing the realy drive to a pulse, as the relay will retain its state with no input.

    However, as the relay will retain any state with no further input, you may find it desireable to change the systen boot to include a routine to drive the new relay into a known state. It's one thing to have the relay maintain a contact closure in a power failure, and another to just have it stay on arbitrarily. One might as well use a toggle switch in this case, as there is no real control once it's set.

    How will the microprocessor be able to distinguish between a boot from a turn-off and a boot from a power failure? This has some importance in the program coding and the control of the latching relay.
  3. Hali

    Thread Starter New Member

    Feb 26, 2007
    To differentiate between normal initialization and after power supply failure, im using the internal ROM of the microcontroller where the status is saved.
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
  5. Hali

    Thread Starter New Member

    Feb 26, 2007
    Thanks....the link really helped me
    The problem is solved