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Seek Help with LED strobe “Security Device” for Rented Home.

Discussion in 'LEDs and Optoelectronics' started by Harpo, Sep 29, 2018.

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  1. Harpo


    Sep 29, 2018
    I’m currently living and working abroad and want to build a “home security device” for the house we’re renting. The front and side yards are well protected by tall security fences and sizable dogs whom have free run of the interior perimeter at night.

    The home is situated on (and against) a hill, such that the rear edge of our roof is only four feet above the ground on the hill behind our house — easy to hop up and walk up to the peak of the roof and down the other side. This level area on the hill directly behind our house is our neighbor’s abandoned kennel with fence and gate in disrepair so local teens come and go to drink and party because the kennel is surrounded by thick rain-forest and affords a lot of privacy. The home’s current tenant doesn’t care about the fence, gate or teens. I don’t necessarily have a problem with their hanging out back there, as long as they don’t climb up on our roof.

    Most of the break-ins and home robberies in this neighborhood are crimes of opportunity — impoverished, desperate people or drug addicts looking for items to steal and sell. Any hint of a reasonable home security system, cameras, etc., scares off 98% of potential perpetrators and while we have cameras on the front and sides (complementing fences and dogs), putting a camera on the roof in back might not be the best idea. Ironically, with no place to mount it out of reach, it could be stolen.

    Given that 98% of potential perpetrators don’t want to be seen or captured on video, I’m thinking of putting a PIR-triggered system that behaves like an image-capture system — something small and sturdy that can be anchored to a fascia board on a dormer near the peak of the roof. The roof tiles extend a few inches beyond the fascia so though outdoors, any unit attached to the fascia board would be protected from rain and sun. A PIR sensor or device mounted on this fascia would have a clear view of any trespassers attempting to gain access to the roof from the area behind our house.

    What I have in mind, is to take a short piece of 3” (diameter) PVC pipe and fabricate a string of LED lights around its inside circumference at the front edge, complemented by a piece of dark, convex plexiglass mounted in its center to simulate a camera lens (surrounded by LED’s). The LED’s would be driven by an actual strobe circuit triggered by the PIR – set for the minimal 5-second “on” duration (PIR Delay setting).

    The PIR would simultaneously trigger an MP3 audio player (circuit board) containing a brief audio sample of a camera shutter, firing in rapid succession (timed to match the strobe blinks). The presence of the plexiglass “lens” (easily visible during the day) in tandem with the strobe and sound effects (at night) would give trespassers the impression they’re being photographed numerous times any time they trigger the system. (A second “email sent” sound effect could follow the “shutter snaps” such that trespassers think the images are being uploaded immediately to the internet. I’m not worried about arming the system during the day. The roof is easily visible to all passersby during the day. The PIR would only need to be active from dusk till dawn.

    The mp3 audio system (project board/enclosure) and speaker could be mounted under the eaves of the dormer hidden from view and the weather.

    It would be best if the PIR could reset immediately after its 5-second “on” cycle so that it’s ready to trigger again immediately upon completion of the 5-second “on” cycle.

    Conveniently, there is a 220V outlet located under the dormer which could power everything, with the understanding that voltages would likely have to be stepped down/converted, to power specific components according to their specifications.

    My biggest question is about where to buy or how to build the strobe circuit. Would the big capacitors generally associated with strobes be required if I’m powering the entire system with 220V? My preference would be to locate the strobe circuit and components inside the PVC pipe behind the LED’s, and mount the PVC pipe to a flange on the fascia board. The length of the PVC tube/housing should be no more than 3.5” such that it remains sturdily attached to the fascia (hard to steal) and well-protected from weather by the overhang.

    The strobe would need to be powerful, but would only have to blink for 5 seconds or so.

    I imagine one could use a pre-built PIR device (available in many hardware stores) and wire it’s trigger/output to the strobe circuit and the mp3 player circuit. One could probably also buy a simple PIR component and wire it along with the mp3 player board into the same weather-proof enclosure. I’m open to any and all suggestions.

    Currently I am living in South America and while there are hardware and electronics stores in this city, we don’t always have access to as many brands as are available in the USA. That said, I have friends whom can purchase items in the US and bring them to me when they come to visit.

    Please bear in mind, that I don’t have a lot of experience designing or wiring electronics but I can solder pretty well and I’m handy with audio.

    Any suggestions and guidance would be greatly appreciated. Thanks!

    roof sensor.png
  2. FuZZ1L0G1C


    Mar 25, 2014
    Speaker: A 1-2W speaker should be loud enough to be heard a short distance away, a mylar cone being more weather / moisture / insect resistant than a paper cone.
    Amp: 1-2W monophonic kit is available at most electronic stores (you'll need an AC/DC stepdown-convertor (power-pack) rated at amp's DC supply (maximum) and amp's load in amps or mA (minimum).
    Sound effect: I thought of my DVR (digital voice recorder) which uses onboard RAM to record, store, and play back business meetings, lectures, messages etc.
    However, mine doesn't have a external remote for controls as it needs user to press buttons on case.
    So my type would need (fairly strong) 220VAC solenoids to force the 'play' button down.
    There may be DVR models that have the remote function, in which case a 220VAC (relay coil voltage) could close (unpowered) N/O contacts across the modded remote 'play' cord function.
    Again, our local RS_electronics has the kit, or ready-built DVR boards in stock, ready to wire up (probably includes a small amp as well).
    PIR: I've never opened a Mains-powered PIR, so no idea what ticks inside.
    Guessing the sensor triggers a small relay or SCR/TRIAC.
    Other answerer's no doubt have a better understanding of this animal.
    My only PIR is a 12VDC intrusion detector mounted in my car, wirelessly linked to it's keychain beeper alarm.
    Appears to work on movement more than IR as sitting still in car then arming it, the alarm behaves itself.
    Any slight movement and the keychain's piezo screecher goes bananas (when armed).
    Strobe: If I understood your post correctly, you want one brief 'pulse' flash, repeated at 5 sec intervals?
    Or do you mean it must fire fast (4-5Hz) bursts of xenon-powered blindness lasting 5 secs?
    There are also circuit kits available (all kits have schematics supplied).
    LED chain: White UB LED's are rated 3VDC (Vf) at 30mA (0.03A) (If), so what DC voltage supply (Vcc) and how many LEDS are series-connected per leg would determine the value of the current-limiting (dropper) series resistor Rs to that leg of LED's, all legs then being parallel'ed.
    The total dropped voltage amount (Vd) is the difference between Vcc and total forward voltages of each diode.
    (Multiply the qty of LED's by Vf per LED).
    If is the the forward current per LED.

    As LED's are series connected, the 0.03A current remains at 0.03A throughout the leg.
    R=V/I (basic ohm's law flipped).
    Rs=Vd/If so

    Vcc=12 Vf=3 If=0.03 Qty=1. Rs = (12-(3*1))/0.03 = 9/0.03 = 300 ohms (don't go less than Rs).
    Vcc=12 Vf=3 If=0.03 Qty=2. Rs = (12-(3*2))/0.03 = 6/0.03 = 200 ohms
    Vcc=12 Vf=3 If=0.03 Qty=3. Rs = (12-(3*3))/0.03 = 3/0.03 = 100 ohms
    Vcc=12 Vf=3 If=0.03 Qty=4. Rs = (12-(3*4))/0.03 = 0/0.03 = 0 ohms
  3. Nisar-von-Voltenbräackter


    May 23, 2018
    All I can think about was that there is no practical security plan if anyone has access with a four foot "bridge." I'm laughing about that one, worse since there's no arial photo.

    Of course, all I can think of would be that lining the roof full of embedded caltrops may certainly discourage anyone from jumping on it and crowbar-ring their way into your house; not sure if your local laws would even allow that option, though.

    Security specialists like to talk about four zones, two outside and two inside. By such time as the villain gets into the home, your only chance for safety (you plausibly have 15 seconds, tops, then only if you hear them) would be a safe room that would take a while to break into, where you keep a bunch of things and may even run a flag up into the outdoors to alert people of you or your family being endanger.

    (Four feet ... like, become a police officer and patrol your community to keep abreast of that drawbridge, matey, because you may as well be selling tickets! :eek:)!

    I respect your interest in electronic security, don't get me wrong. But I'd wish I could help you with a serious security plan :(
  4. FuZZ1L0G1C


    Mar 25, 2014
    Instead of Flash-strobes, sound effects, etc, what about 2 or more solenoid-triggered automatic machine guns aimed crosswise across the rooftop?
    Then several rows of rollers, which release brakes only when activated, tipping perpertator(s) into a crooc-filled moat, in case rounds miss?
    Of course, you would have to remember to disable the system when cleaning leaves from your guttering!! :D
  5. Harpo


    Sep 29, 2018
    Greetings FuZZ1L0G1C and thank you for your comprehensive response. The audio aspect of this project is fairly straightforward with off-the-shelf circuit boards and hardware from what I can see, as audio is my thing and I do appreciate your input. The biggest challenge is building and timing the strobe and so your detailed info on the LED's is surely much appreciated. To clarify, the 5-second "delay" referred to in the OP refers to a term specific to a PIR. Having triggered an electric power circuit powering for example, a flood light, the term "delay" defines the length of time the PIR allows the power to remain "on" prior to resetting and disconnecting the power. It would make more sense if they called this PIR term something like "duration", but they don't so it's confusing. What I'm looking for is a strobe blink rate of about 4 per second, ideally for about 2 seconds, but I can't find a PIR with a 2-second "delay". The shortest I've been able to find is a 5-second delay. Thanks again!
  6. Harpo


    Sep 29, 2018
    Hi NvV... You might find this even more amusing, but it's not 4 feet across... it's 4 feet vertical. :eek: One can literally hop right up on the roof while standing in my neighbor's abandoned kennel/party zone.

    My situation isn't quite as dire as you imagine. I'm not so much worried about home invasion given that all access points to our home are well covered by an existing security system — even from the roof. I'm primarily concerned about about partying, unruly teens climbing upon and damaging the tiled roof and the occasional desperate teen (minor) that might want to break in from the roof if and when we're not home. But thank you kindly for taking a moment. I do appreciate it.
  7. Harpo


    Sep 29, 2018
    Great plan, Fuzz! :D And we were only gonna hire a couple of 24-hour trolls (not forum trolls... actual trolls) to pour hot oil from the peak of the roof when intruders appear. But your plan is better! :)
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