circuit needed

Discussion in 'General Electronics Chat' started by mart_1986, Dec 13, 2009.

  1. mart_1986

    Thread Starter New Member

    Dec 11, 2009
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    im after a circuit that will allow me to open and close electric blinds using a 5v motor which it hooked up to a worm gear.

    the circuit needs to run off 1 power supply which is on a timer so at 9am the blinds open then at 3pm the blinds close i will be using limit switch to stop it to fully open
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    This will do it for you:

    [​IMG]

    Just change all the 12v to 5v.

    The relays will only have their coils energized when the motor is supposed to run. Only one relay coil will be energized at a time. The limit switches break the coils' path to ground.
     
  3. mart_1986

    Thread Starter New Member

    Dec 11, 2009
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    thank you mate
     
  4. Harrington

    New Member

    Dec 19, 2009
    86
    3
    Why not use an H Bridge Driver utilizing Fets or Transistors far better design
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Not necessarily, relays are robust, they aren't static sensitive, the parts count is low, and many cases they use screw contacts. All of which make for a really simple project.

    The only critique I would have is D1 and D2 aren't needed if there aren't any solid state parts.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Nothing wrong with using an H-bridge. I was just trying to keep it as simple as possible; no PCB required, and the relays could be obtained at any auto parts store.

    Bill,
    The diodes help extend the life of the switch contacts. Without the diodes, the reverse EMF across the relays' coils can get mighty high, mighty quick. This will cause prolonged arcing across the switch contacts as the connection is broken, which will burn and pit the contacts, causing premature failure. The diodes are cheap insurance.

    Had I wanted to really "do it up right", I would've used diodes on both sides of the motor to +V and ground in reverse bias. That would help to prolong the life of the relay contacts. However, I was trying to keep the schematic as simple as possible so that it would be relatively easy to understand.
     
  7. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    2 more variations, also simple circuits.

    S1 is unit power on and off. Shutting this switch OFF will stop the shade in any desired position.

    S2 is the on and off coming from the 9:00 / 3:00 timer.

    S3 and S4 are double pole limit switches that will stop the shade when it reaches the end of stroke (opened or closed). It accomplishes this by putting negative on both poles of the motor.
    When the timer changes positions, the polarity will change on one of the limit switchs causing reverse direction of the motor.

    This is an adaptation from an old Deutz Diesel throttle actuator for high-lo throttle position.

    It works extremely well in any animation requirements also.
    Like animated santas etc...
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    VoodooMojo,
    Interesting - but one issue is current draw.

    In the circuit I posted, only one relay coil will be energized at a given time - and only energized while the motor is running. The limit switches only carry the ground side relay current, which is pretty typically low, which enables the use of very small limit switches.

    When the shade has reached the limit of travel in one direction or the other, the relay coil's ground path is broken, and no further current is used until it is desired for the shade to travel in the other direction.
     
  9. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    point well taken Sgt,

    300ma is what 2 large automotive type relays would take at 12 volts energized simultaneously.
    90ma is the draw of 2 smaller type 12 volt relays.

    5 volt relays would draw a considerable amount less current.

    I am not sure what mart_1986's power source is.
     
  10. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    photos attached
     
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