Make a latch (flip-flop) using two relays?

Discussion in 'General Electronics Chat' started by mank, Apr 14, 2011.

  1. mank

    mank

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    Had an interview today. There was a test. They wanted me to draw a diagram and this was what I was supposed to do:

    "Draw a latch (flip-flop) using two relays. Show inputs and outputs"

    I have never seen relays used in this way. I have been a Navy Electronics Technician and in the field for over 30 years.

    I just could not figure out how to do the 'toggle'.

    Anyone got any ideas?
    mank, Apr 14, 2011
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  2. mank

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Perhaps we should wait a few days, just in case...

    Here's some hints.

    1) can I wire a relay so that once power is applied, it latches on?
    2) how could I, with another relay closing, reset this?
    3) can I interconnect 2 of these together?

    I've never considered this either. I think the test was not so much about the flip-flop as how you think on your feet.

    I've posed questions of this nature to potential job applicants before. I was more interested in how they approached an unfamiliar problem, than how they solved it.
    (*steve*), Apr 14, 2011
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  3. mank

    Laplace VIP Member

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  4. mank

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    But you can do it with just relays and switches.
    (*steve*), Apr 14, 2011
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  5. mank

    baileya

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    flip flop using two relays

    To answer the question on the flip flop using two relays, it can be done utilizing two timers , one timer to switch between the relays and the other timer to reset the circuit
    Start with one relay instantly energised , then timed off. Next switch on the other relay and provide a hold contact . The second timer is used to stop and reset the circuit allowing it to start the cycle all over again.
    I can draw out a circuit wiring diagram but not sure how to post the circuit on this site
    Cheers
    Arthur
    baileya, Jan 31, 2013
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  6. mank

    Osmium

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    A lot of years ago, I made a flip-flop using two relays and two switches. I think I also had a light globe to show the state! Just like Steve says, think about it...

    --- Warning: Nostalgia piece...
    The school radio club used to get a lot of surplus telephone switching gear and other bits and pieces. Full of relays and all sorts. Kept us happy for ages! [btw our surplus gear was well and truly valve era. My first transistors to play with were OC45s and OC71s - and expensive!!]

    -Roy
    Osmium, Jan 31, 2013
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