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Probably a simple question, but...

Discussion in 'Electronic Basics' started by [email protected], Oct 23, 2005.

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  1. Guest

    I want to have a motor started by tripping a relay when someone breaks
    a beam of light (dark activated relay). I then want to power to the
    motor to cut when it makes one revolution by tripping a rocker switch
    or something similiar, which would cut the power (close the relay). I
    already have the circuitry for the beam of light relay.

    I initially thought a second relay, between the light relay and the
    motor would do it, but I cannot think how to wire it up where the
    middle relay stays on. Wouldn't it just open and close real quick as
    the light relay opens and closes?

    What do I need to do to have the dark activated relay activate another
    relay that stays on and runs my motor, then allows my motor to turn the
    middle relay off when the motor trips a rocker switch upon one
  2. Rich Webb

    Rich Webb Guest

    Nowadays, with small, cheap microcontrollers so available something like
    this might be easier to throw together as a digital system rather than
    with relay logic. However ...

    | .-. |
    o---------( L )----------------------o
    | '-' |
    | . |
    | . |
    | . |
    | L1| | KA .-. |
    o-o--------| |---------o---( K )-----o
    | | | | | '-' |
    | | | . |
    | | | . |
    | | | . |
    | | B1 | . |
    | | | |/ A1| | | . |
    | '--|/|----------| |--' . |
    | /| | | | . |
    | . . . |
    | . ........... |
    | . . |
    | . . |
    | . A2| | .-. |
    o-----------------| |------( M )-----o
    | . | | '-' |
    | . . |
    | . . |
    | . . |
    | . . |
    | . . |
    | KB.-. M1| | |
    '---( K )-------------------| |------'
    '-' | |
    (created by AACircuit v1.28 beta 10/06/04

    1. An event at light sensor L shuts L1, energizing KA.
    2. KA shuts sustaining relay A1 and motor power relay A2.
    3. When the motor reaches the end of its travel, it shuts M1.
    4. M1 energizes KB which opens B1, turning off KA.
    5. When KA is de-energized, A2 opens, turning off motor M.

    This assumes that the motor is in the active zone holding KB energized
    long enough to drop KA, and that the motor coasts through far enough
    after being turned off to release KB at the end of travel. Otherwise,
    use a timer for KB with a fixed "on" state time.

    If the light sensor stays active, KA stays energized and the motor keeps
    running, which may or may not be desirable depending on the actual

    Personally, I'd use something like an ATtiny11 (8 pins, internal
    oscillator, priced at $0.54 qty one at Digikey) with the light sensor,
    one microswitch at the motor, and one relay for the motor power.
  3. John Fields

    John Fields Guest

    Use the output from the beam-break detector to fire a one-shot which
    sets a latching relay (or an RS latch) which drives the motor-run

    Use the output from the motor switch to fire another one-shot which
    resets the latch, de-energizes the motor-run relay and stops the

    Tell us what kind of voltage and current the motor needs to run on,
    what the beam break relay and the motor switch look like, and I'll
    draw you a schematic if you want one.
  4. Guest

    Rich - no question that a microcontroller would be the way to go as I
    understand that logic better than going the electronic relay route. I
    do a lot of programming in my job and having an output be triggered by
    an input is much easier for me to wrap my head around. Unfortunately, I
    do not have the time to get all the pieces, learn how to use it and
    then learn how to implement it. After this project is over I will begin
    learning how to use microcontrollers. I have never heard of the
    ATtiny11 (really just the PIC series microcontrollers), but will being
    looking into this soon. Thanks a lot for the reply.

    John - I had not heard of a latching relay. This appears to be exactly
    what I am looking for. I knew that I probably needed some kind of
    elecronic switch that stayed in it's last position, but didn't know
    what to look for. Would I need an "impulse relay" to do this? Is this
    something I can get from Radio Shack?

    Everything will be 12V. I planned on building the dark activated relay
    like the one on the left side of the page here:

    only with using parts rated at 12V. I was just going to use a rocker
    switch to turn off the current from the motor. Is there a better idea
    than using a rocker switch? I planned on the motor just spinning around
    and having it hit the rocker upon one complete revolution. If there's a
    better way here let me know.
  5. Guest

    What if the light switch applied power for a period of time (say 60
    seconds using a capacitor)?

    How would I get this to work:

    The motor gets power and turns. When it does 1 revolution, it hits a
    switch (SW1).

    The SW1 closes, it activates a relay (R1) that cuts power to the motor.
    As long as power is coming from the light switch, R1 keeps cutting
    power to the motor. When power is cut after 60 seconds, R1 goes back
    and once again allows power to the motor when it is triggered.

    Would this work? If so, can someone draw it up - I can't seem to make
    sense of it.
  6. Guest

    Jamie - The message I posted immediately after your first reply was
    done before I read your first message. I think we are thinking the same
    thing though. Could you do a simple schematic so I could get a visual?
    Just the part after the light switch.
  7. John Fields

    John Fields Guest

    There is a better way. The detector circuit shown doesn't have a
    clearly defined switching point and should be designed around a
    comparator. I don't know, physically, how you plan to mount the
    rocker switch, but unless the motor continues past the point where
    the switch cuts the motor off and returns the switch to the ON
    position, you'll never be able to start the thing again!

    The solution there is to use the one-shots and latch I recommended
    earlier since the stop and start aren't dependent on each other.
    I'll post a schematic for you on abse sometime today.
  8. Jamie

    Jamie Guest

    to make your job easier since it looks like your looking for a simple
    use the optical method as you are now to hold on a relay.
    use a normally closed proximity switch that would hold a control lock
    loop closed on this same relay when the sensor is not being tripped.
    the idea is to position the optical in such a way that it will say on
    long enough to get the motor rotating enough to move the index away from
    the proximity switch so that it will complete the lock loop control line
    which will hold the relay on until the rotor comes all the way around
    and trips it once again to open the lock loop.

    basically a double pole relay is needed here, one pole to start your
    motor and the other pole use to create a loop lock.
    the magnetic switch will break the loop when it's on target.
    just remember that the optical must be position so that is will say on
    long enough to get the magnetic off target so that the loop will be closed.
    actually, you could use magnetics on both sections..
    you could also use a flip flip and use only 1 sensor..
  9. Jasen Betts

    Jasen Betts Guest

    Just have the rocker switch cut the power to the whole circuit.

    or do you one it to start again next time the beam is broken?

  10. Jamie

    Jamie Guest

    have the light switch start a one shot timer relay that
    will energize the main relay for the motor.
    have the stop switch also loop around from the 120 control
    line source to directly energize the main relay..
    by the time the one shot timer has expired, the motor shaft
    will be well out of the position of the light switch and the
    stop switch will be off it's stop position in the close state
    keeping control power to the main relay coil.
    when the switch hits the stop position again, it will simply
    open up and thus turn off the main relay for the motor.
    like i said before, you can do it with out a one shot timer
    if you simply position the light switch so that what ever
    trips it will stay in view long enough for the motor to turn enough
    to get the stop switch in the close position.

    Real Programmers Do things like this.
  11. ehsjr

    ehsjr Guest

    To do it the way you mentioned, you need a double pole relay in
    addition to your existing beam of light relay, plus the rocker
    switch (or whatever) you mentioned.

    I'll assume 12 volts for the circuit below. RY1 is your existing
    beam of light relay.

    RY1 Contact
    +12 ---+---o o----------------+---[RY2]--- Gnd
    | |
    | o
    | / /
    +---o o--------------o
    RY2 Contact #1 Rocker Switch

    RY2 Contact #2
    o-------------- to motor
    +---------------- to motor

    How it works: When RY1 (beam of light relay) energizes, the
    contact closes and RY2 is energized. RY2 contact #1 provides
    a path for 12 volts to reach the RY2 coil, through the rocker
    switch, to keep RY2 energized even after RY1 is no longer
    energized. RY2 contact #2 is used to complete the circuit
    to the motor. When the motor spins and activates the rocker
    switch, the path to RY2 is interrupted, RY2 denergizes, and
    the motor is turnrd off.

    RY2 is a double pole relay, chosen for a contact rating that
    can handle your motor's rating.

  12. Jasen Betts

    Jasen Betts Guest

    neither can I. try this.

    ----+--+------+--------------------+------------- +12
    | | | ||+ | .
    | | +--[R1]----+----||---+ .
    | | | ||C1 .
    SW2 | | SW1 | o .
    | o | |-| .
    |-| | | o o-----.
    | o | _-~ | _-~ |
    | `--~. o----------)-----~. o--. |
    | . | . | +----.
    +-----+-. +-----+-. | | |
    | | |RY1 | | |RY2 | | |
    | | | | | | | | |~|
    | | | | | | | | /~~~\
    | .--+-' | .--+-' | | |motor|
    | | | | | | | |
    | | +--)---------' | \___/
    | | D1 | | |_|
    `--)---------|<---------)------------+ |
    | | |
    ------+--------------------+-----------------+--- ground

    sw2 is your light (dark) sensor when it closes relay one energises
    while relay 1 is energised current flows through its contacts and through
    relay2's contacts to run the motor, should switch 2 be released current also
    flows through the diode D1 maintaining relay 1 in the on state.

    when the motor has done a full rotation it closes SW1

    current flows through the capacitor and closes relay2 this breaks the
    circuit feeding power to the motor which stops and if SW2 is now open
    there is no source of current to energise RY1 which opens

    if SW2 is still held closed current flows through the ry1 contacts and the
    now closed RY2 contacts and maintains RY2 in a closed state until SW2 is
    released and RY1 opens

    When RY1 opens the power is cut to RY2 which opens
    immediately in the case where the motor has progressed slightly past SW1
    before halting or after C1 has charged up in the case where SW1 is still

    for motors upto 15A automotive headlight (RY1) and horn (RY2) relays
    may be suitable

    D1 can be any GP rectifier diode (eg 1N4001)

    if R(ry2) is the resistance of the relay 2 relay coil.
    R1 should be about 10 times R(Ry2)
    and C1 should be about 10000/R(Ry2) microfarads

    for SW1 a microswitch with a roller on its actuator arm would be a good
  13. quietguy

    quietguy Guest

    Would using a cam on the motor to operate micro switches do the trick?

  14. That's pretty much how windshield wipers work, at least on older cars.
    A switch kept applying power to the motor until the cycle was completed.
    I have no idea what they do now, prolly pretty much the same thing.
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