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  • Motion Detector Audio Trigger

    I'd like to build a small battery powered amp & speaker unit that will play back an mp3 when triggered by a motion detector. PE has a number of wonderful options that will handle everything but the motion trigger. Anyone have any idea or recommendations on how to add that last feature? Thanks in advance.

  • #2
    Sounds like you need to look into Audrino or Rasberry Pi. They have I/O modules that could pretty easily be rigged for motion detection, and open source software to play MP3's. You'll need some C+ skills I imagine. I don't have direct experience, so that's about as much help as I can give.
    Electronics engineer, woofer enthusiast, and musician.
    Wogg Music
    Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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    • #3
      I like to keep things simple. You can buy simple inexpensive motion detectors that are relatively easy to interface.

      Here is an example: https://www.harborfreight.com/led-mo...ght-95276.html
      Don't worry, if your parachute fails, you have the rest of your life to fix it.

      If we all did the things we are capable of doing, we would literally ASTOUND ourselves - Thomas A. Edison

      Some people collect stamps, Imelda Marcos collected shoes. I collect speakers.:D

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      • #4
        Google low voltage motion sensors. They're made for low voltage home security systems. There are a myriad of choices: infrared, led, microwave, ignore small animals/pets, etc. A 12V or 24 V model may be able to run off the same battery as audio system (simplification). Pay attention to the idle power draw for your battery based system. And the sensor's max switching current. You'll likely need a relay between the sensor and the audio systems supply voltage if the sensor can't handle the audio system load. On a positive note, they are cheap being massed produced for the home security market.

        Here's one I research some 15 years ago. I never followed through on that project.

        As you can see from the spec.'s, it draws 12 ma on idle. While that does not seems like a lot, that equates to 2 aH over the course of a week.

        Also, the sensor's trip contacts are rated at 50 ma. So you would need a 12 V relay with a coil draw less that that. Then that relay's contacts would close the power connection to the audio system. You may need a latching relay. The sensor's spec.'s mention 1, 2 or 3 pulse count. I'm not sure if that means the contact closure is pulsed instead of steady state when the sensor detects intrusion.

        Lastly, you didn't really give a lot a details about your planned system (e.g., where, how often, required up time between battery charges, etc). A description of how you plan to use it is key. That would help us better help you.

        Click image for larger version  Name:	Sensor.png Views:	0 Size:	651.1 KB ID:	1433531
        Last edited by Millstonemike; 03-04-2020, 09:11 PM.

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        • #5
          Thanks for the response. The links are very much appreciated.
          To explain the project further, I want a system that could be added to photos or artwork and add an audio element. For example, as you approach a photo of a forest, you would hear forest noises emanating from the photo via exciter speakers. Or, perhaps a short commentary by the author or artist. It needs to be small enough to fit behind a (deep) frame. It doesn't need to run 24/7. I can change batteries, I'd just to like to do it weekly not daily. It doesn't need to be loud. In fact, loud is bad. I want just enough power for good sound at low volume.
          Thanks again.

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          • a4eaudio
            a4eaudio commented
            Editing a comment
            I don't know the solution, but that is a really cool concept!

        • #6
          And by the way... This is my application. But if someone wants to start building these, there is a HUGE market in the Halloween Home Haunt community looking to trigger spooky sound effects. If you could keep the price point under $50 you could sell a lot of them. Under $100 you would sell fewer but could have a larger margin depending on your costs. FYI

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          • #7
            You'll need an audio system that starts to play from the beginning of the program each time it is activated by the sensor.

            The pic.'s below: The sensor is infrared based and will detect objects (people) a maximum of 2 ft away. The audio module lets you record your narrative with it's built in mic. Playback is started by pressing a switch to close a contact. That can be done by the sensor. It has settings (on board jumpers) to play the entire recorded message once when activated. Both units work off 5 V DC (6 V would be fine).

            The problem I see is battery power for a "set and forget" system with recharge once per week. The sensor consumes 25 ma and the audio module idling will add to that, say another 25 ma for a total of 50 ma idling. Not a lot but it adds up. Over 12 hours a day, 10 days (some reserve over the 7-day weekly replacement/recharge cycle) equates to 6 aH battery capacity. Three C-Cell alkaline batteries could work. But you'd be replacing them each week or so. A sealed rechargeable leadacid AGM/SLA (lead battery would weigh 2 lbs and be 6" by 4 " by 1.5" in size. And a Lithium rechargeable would run upwards of $35 plus the associated recharging circuit.

            Powering this thing is greatly simplified with a user activated button (like in zoos) or AC wall power using a plug in USB charger (like a phone charger).

            Click image for larger version  Name:	Sensor.png Views:	0 Size:	257.2 KB ID:	1433561

            Click image for larger version  Name:	Audio Module.png Views:	0 Size:	211.3 KB ID:	1433562

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            • #8
              I glossed over the thekorvers's link on first pass. That Harbor Freight t unit, with it's 4 AA batteries can provide the power to the audio playback recorder in my previous post (with a little bit of surgery). In the unit's reviews on the HF website, one buyer said his has been going strong for over 2 years on one set of batteries. Instead of providing light (or in combination with light) the activated unit can power the audio module. The only question - whether the audio module will play its stored program on power up (with the trigger switch hardwired on) or whether it needs the trigger switch after power up. Only testing an actual unit would confirm that potential issue...thekorvers sensor also has a longer "field of view" at at an advertised 8' if that's a plus.

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              • #9
                This is great info. Thank you very much for the recommendations and links.

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