Advice/Help Getting Started - Flasher with Low Trigger and Timeout

Discussion in 'The Projects Forum' started by Clemsonee, Jul 4, 2011.

  1. Clemsonee

    Thread Starter New Member

    Jul 4, 2011
    Hi everyone,
    I'm new to the board and trying to devise a scheme for some effects I'm trying to do for some LED rope lighting that is a part of some accent lighting for outdoor decorations I'm doing.

    I used to know circuits pretty well and studied EE in college but a decade in power distribution hasn't been kind to my ability to recall the intracacies of building my own custom circuits. I'm hoping a little advice and friendly discussion might bring me back.

    Anyhow, what I'm trying to do is create a trigger/flasher/timeout combination circuit that when triggered will produce an output to a relay to 'blink' three times and then return to an "on" state until re-triggered. In other words, I would like for the lighting to be on until someone walks through, upon activation blink three times, and then return to being steady on again. If a normal 'low' output circuit is easier or less complicated I can always flip flop the output based on whether I use a n/o or n/c output relay so the actual output of the circuit being high or low normally isn't as much of a concern as the blinking and timeout functions.

    My input will be from a 12v battery which will power a 12v infrared optical sensor (similar to garage door safety beams) through this circuit. Thus it will require fairly fast and moderately sensitive trigger as I need it to be quick enough to pick up an ankle passing through the beam at average walk/run speed. Once it is triggered by the sensor I want the circuit to blink 3 times (at approximately 0.5 seconds each) and then return to "on" state.

    One catch is that I was hoping to use a spare set of garage door sensors that I have for this project. The sensors aren't truly a high or low output in the +12vdc or 0vdc sense. The are actually around +10vdc and are active high at +12.5vdc when the beam is broken. I'm not sure if this would affect the trigger chip for the circuit.

    I know I'm a newbie to the forum and any help would be greatly appreciated. This is definitely one of those times when I wish I hadn't sold so many books back at the end of the year in my school days, but thanks for any help and advice!!
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    The easiest thing I could think of is having two 555 circuits in series, the first one triggered by your sensor and the second one triggered by the first one.

    The first one a monostable enabling the second one (an astable) for the time the second needs to give out the 3 pulses.

    Also can use the 556 which already has two 555.

    Be careful to use bypass caps and to avoid negative transients on the trigger input (could kill the chip)