Electric window blinds

Discussion in 'The Projects Forum' started by boatsman, Aug 9, 2013.

  1. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
    I have window blinds that are raised and lowered with an electric motor (220 VAC 50 Hz). I want to raise and lower them using a time clock. The problem is that the time clock will completely open or completely close the blinds whereas I want to be able to raise or lower the blinds to varying heights. If I use a 555 timer circuit to vary the time the motor is switched on (for a period between 1 second to 1 minute) I have the problem that the time clock switches on for a minimum period of 15 minutes whereas I need a single pulse to operate the 555 circuit. Anyone have any ideas how I can solve the problem?
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,148
    3,058
    The 555 one-shot (monostable multivibrator) circuit can be non-retriggerable. That means once the trigger goes, it will go through one cycle and that's it.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,033
    3,241
    If you AC couple the trigger input (triggers on negative edge), such as here, it will work with a long input pulse.
     
  4. boatsman

    Thread Starter Senior Member

    Jan 17, 2008
    165
    390
    Thank you wayneh. How do I set it up so that even if the circuit gets electricity for 15 minutes it will only operate the timer once? Also the next time the timer is triggered (after several hours) it will reverse the direction of the blind. I thought of using 12VDC relays to reverse direction but maybe there's a simpler solution.
     
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