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PIR LED 12V light circuit recommendations wanted.

Discussion in 'LEDs and Optoelectronics' started by Sidecar Bob, Dec 28, 2021.

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  1. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    I bought some HC-SR501 type PIR units to experiment with. Knowing nothing about this technology I assumed that if I use a 12V power supply I could run a 12V LED light from it but that didn't work. I did some research and checked the spec sheet again and learned that regardless of the supply voltage the PIR unit has 3.3v (TTL) output.
    I did a bit more research and it indicated that I could use a transistor to drive the LED, which would have been easy for me to figure out 30-40 years but but over the decades I've forgotten a lot.

    Can someone please recommend a simple circuit for this?
     
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Simpler to use a logic level mosfet like an IRLZ44N........
    Here is a circuit using a IRL540N ......same same....5v supply replaced by your 12v naturally.
    R1 about 100R....R2 around 10k....common the negative on both supplies.

    IRL540N.jpg
     
  3. Sidecar Bob

    Sidecar Bob

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    4
    Dec 19, 2021
    I've never worked with mosfets (or any other kind of fet) before but I have a pile of regular transistors so I'd rather use what I have if I can.
     
  4. Martaine2005

    Martaine2005

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    998
    May 12, 2015
    What LED light are you wanting to use?
    Can you post the specs.

    Martin
     
  5. Bluejets

    Bluejets

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    1,101
    Oct 5, 2014
    Well then, like Martin says, you're going to have to supply some more details.
    Circuit I showed would work straight up, transistors will need some working out based on your reply.
     
  6. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    It is a generic eBay/China side marker light similar to these. I have low voltage (12V DC) lights on the side of the garage that run dusk to dawn and I bought a bunch of these a few years ago to mount inside the garage and connect to it (I figured at the time that it cost less to run half a dozen of these all night every night than it would to turn on the main lights for a minute a few times per week).
    https://www.ebay.ca/itm/384327257796

    That eBay listing doesn't give any power or current specs and to be honest I have never measured the current to one of them. The closest I've come was plugging the 12V supply in with my plug in power meter and comparing as I added them to the circuit; At the 110V AC mains plug each one increased the power by 0.5W.
    I also mounted 4 of them on the bottom of the cabinet in the basement kitchenette to light up the counter, powered by a 12V 1A supply and the power meter said 0.5W for just the supply and 2.5W for the supply + 4 lights.

    I figure that works out to about 42 mA per light but I can connect one to a supply and confirm that when I am in the shop later today and let you know.

    For this project I need to use 1 of these lights but it would be nice if I could add another later on.
     
  7. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    How about that. The actual current I measured with the 12V supply I want to use and the light I've already mounted in the box (next to the sensor) is only 26mA (measured with 2 meters to make sure).
     
  8. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    Nothing?
     
  9. Cirkit

    Cirkit

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    Oct 28, 2015
    Which transistors do you have?
     
  10. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    I'm not in the shop right now so I can't list them all but I have a bunch that are equivalent to 2N2222.
     
  11. Cirkit

    Cirkit

    141
    10
    Oct 28, 2015
    The specifications for the HC-SR501 seem to suggest it will operate from 12V. So you can connect the TTL output via a 1k resistor to the base of your transistor and drive a fair few of your LEDs in parallel.
     
  12. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    The HC-SR501 will definitely work with a 12V supply. When I was trying to figure out what was going on I had one connected to the 12V supply I want to use for this with a 3mm LED + resistor on the output and left it running on the end of the bench for a few days
     
  13. Sidecar Bob

    Sidecar Bob

    44
    4
    Dec 19, 2021
    I'm in the shop now and looking at my bin of transistors. I have
    - a bunch of "generic" TO-5 types with numbers like CK913, CK914, 2n414, RCA 40595, a lot that aren't marked and a bunch with IT ID GA stamped into them.
    - some TO-46 marked 267819
    - some TO92 marked 70C 7427 and 70C 7411
    - an RS-2021 brand new in Radio Shack package (says 2N2907 on the back of the card but the card shows a TO-18 and this is a TO-92)
    - a few other plastic/epoxy types with numbers like 636ge, 886GE, 2N3393, GE5128 and an assortment of unmarked ones (for some reason I have it in mind that some of these are equivalent to 2N2222)
     
  14. Sidecar Bob

    Sidecar Bob

    44
    4
    Dec 19, 2021
    I came across this circuit that looks promising. He posted a link to a video of it turning on LEDs on his stairs. What do you think?
    https://i.stack.imgur.com/7tT4P.jpg (The thread asked how to add an LDR so the lights wouldn't come on in daylight but that doesn't matter for my project).
    [​IMG]
     
  15. Sidecar Bob

    Sidecar Bob

    44
    4
    Dec 19, 2021
    No opinions?
     
  16. Sidecar Bob

    Sidecar Bob

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    Dec 19, 2021
    I just realized that the link in post #14 is to the drawing, not where it came from. Here's the correct link
    https://electronics.stackexchange.c...-controlled-by-pir-want-to-add-ldr-to-project

    I also realized that the transistor's terminals are not labelled. Based on other similar circuits I see online I think it is safe to assume that the emitter is connected to the negative line.

    Once I removed the switch, indicator LED and 7805 that I don't need it looks like this. Is this all I need to do?
    PIR LED 12V.png
     
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