Need help with relay for controlling electric projector screen, schematic included

Discussion in 'The Projects Forum' started by Picarro, May 11, 2014.

  1. Picarro

    Thread Starter New Member

    May 11, 2014
    3
    0
    Hello fellow AAC members,


    I have bought an electric projector screen. I cheaped out, and got the version without a 12v controlled drive. Now I've gotten tired of having to manually press the remote, and I want to make it controlled by the 12v port on my projector.


    The screen came with a remote control, and I have opened this and want to use it. In theory it's simple enough. If I short the two pins connected by the switches the screen goes up or down, depending on which pins I short.
    My projector puts out a 12v impulse when it is turned on, and an impulse when it is turned off. I want to create a system that "splits" the 12v impulses. The first impulse needs to go to a relay that shorts the "down" switch, and the second impulse needs to go to a relay that shortens the "up" switch.


    My problem is, that I do not know which types of relays that I need. I think I need a bistable relay for "RLY1" in the drawing, and normal relays (2&3) that are "on" when power is applied, and "off" when the power goes off. This way I don't continously short out the pins draining the remote of power.


    Looking at the schematic, the voltage that powers the first relay to change, also powers the second relays to change. This way, no secondary PSU is required for the voltage needed for them to shift.
    The 1 and 2 on the "Remote PSU" simply denotes + and - poles.


    Here is the schematic, [​IMG]



    TLDR; what kind of relays do I need for 1 and 2-3?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    I moved your power supply. Whatever voltage that is, buy normal relays for that voltage, SPST, and I think you have your contacts drawn backwards.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    IMO, you need a ratchet relay for RLY1. That's a bistable relay with a single mono-polar coil. Each time its pulsed it changes state.

    If pulse is long enough it may be routed thru NC or NO contacts, Eliminating need for other relays. If source can supply enough current, pulse might be "stretched".

    If not RLY2 and RLY3 must be "interval" timers. These output a "one-shot" pulse while input is maintained.

    This can also be done (IMO)
    with one of the low cost timer modules from Ebay.
    [​IMG]


    By connecting the input 12V thru the NC contacts, it should simulate an interval timer. Output "on" thru the "time delay on" period, then remaining off as long as input is powered.

    Have you thought of timing issues?
    If each pulse toggles function, it may not stay in sequence!


    Ratchet relay.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    What voltage does the remote operate on?
    How long does the 12V impulse last?
    I'm thinking perhaps a CD4066 could replace the relays.

    Edit: I'm also thinking this seems to be a lot of trouble to go to just to avoid pressing a button twice per session :))
     
    Last edited: May 11, 2014
  5. Picarro

    Thread Starter New Member

    May 11, 2014
    3
    0
    @Alec, the remote operates on 12v as the projector, so I'm lucky in that regard. As for the trouble, it's mostly for the fun of learning it.

    @Inwo, do you have an eBay link for that timer?

    As for the sync issues, the remote will be placed in the media cabinet, so if it gets out of sync I can simply walk over and press it.
     
  6. eetech00

    Active Member

    Jun 8, 2013
    650
    112
    hi

    Alec_T has some very good questions. You can't really come up a solution until
    those questions are answered. For example, how much current is available at
    the 12v output?

    eT
     
  7. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
  8. Picarro

    Thread Starter New Member

    May 11, 2014
    3
    0
    The 12v output is 0.2 amps, but I have a separate 12v 2A supply at hand if needed.
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
    315
    Then you will need a driver or solid state flip flop for RLY1.
    The .2A will not drive the ratchet relay.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,800
    1,103
    Do you have to keep your finger on the remote button for the whole travel period of the screen, or is a brief press of the button enough?
    Does the screen have limit switches so that it auto-stops when fully up or down?
    Is the 'on' pulse from the projector identical in amplitude and width to the 'off' pulse?
     
    Last edited: May 11, 2014
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