Shop Learn
PIR Triggered Relay Circuits (Motion Activated Light) — Parallax Forums

PIR Triggered Relay Circuits (Motion Activated Light)

Chris SavageChris Savage Parallax EngineeringPosts: 14,406
edited 2013-11-10 13:57 in Accessories
I posted some circuits in my blog for activating a light or other device using a relay triggered by a PIR sensor and timed by a 555 Timer IC. No microcontroller required.

http://forums.parallax.com/entry.php/3960-PIR-Triggered-Relay-Circuits

Comments

  • garyggaryg Posts: 420
    edited 2013-11-08 22:21
    Hi
    I really like both the single and dual relay boards used with Parallax PIR sensor.
    The 555 timer in use with the relay boards is a good, simple circuit.

    A couple of simple questions:

    Are the single and dual relays driven through a transistor to reduce the
    current required by the relay coil?

    When you first apply power to the entire circuit, does the 555 timer output misfire?

    When I've used 555 timers in the past, I had trouble with the 555 timer misfire when power is 1st applied.
    I'm thinking that with this circuit, since the PIR on powerup will hold its output HI for about 40 seconds or so
    that a misfiring 555 timer will not affect it's operation.

    Thanks for what you do.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2013-11-10 13:57
    Hello,

    The Single and Dual Relay Boards each have their own transistor drive circuits on-board, which is why the output of the 555 can safely go directly to them. These boards also include the flyback diode for protection.

    It's been more than a few years since I dragged out a 555 for something and this circuit was a perfect reason to do so. A re-triggerable timing circuit without a microcontroller. However you did already suspect what I was going to mention. Whether the 555 glitches on power-up or not (I don't recall whether I have experienced that or not) the PIR will certainly cause it to trigger initially anyway. Of course, my experience with most outdoor motion activated lights is that when you first turn them on the light comes on initially for the timing cycle anyway. And since my purpose was to emulate the functionality of one of those lights I figured that would be a useful feature anyway.

    If you have any other question, feel free to ask. :nerd:
  • Does anyone happen to have a copy of the original ZIP for this project?

    Sadly, I posted this to the Blog section back in the day and that is gone. My archives were lost when I lost everything in 2018. If someone happened to have downloaded this and still has a copy, I would be grateful to get a copy again.

  • @SavageCircuits said:
    Does anyone happen to have a copy of the original ZIP for this project?

    Sadly, I posted this to the Blog section back in the day and that is gone. My archives were lost when I lost everything in 2018. If someone happened to have downloaded this and still has a copy, I would be grateful to get a copy again.

    While I don't have your original zip file for this project, I was able using the Wayback Machine find your posting about your project. The Wayback Machine didn't archive the actual files unfortunately, but I was able to find in my stash one of your circuit PDFs.

    I've attached a zip file containing what I found, along with other documentation concerning the Dual Relay board. I have a number of the Dual Relay boards, they are very useful...

  • Francis, thank you for sharing what you find. Obviously, my request still stands for anyone who may have my original ZIP with all the schematics, but I am very appreciative of what you dug up. It will allow me to at least put something up on the page for now. Thanks again!

Sign In or Register to comment.