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Trigger 12VDC truck horn with Ring doorbell

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Chamski, Sep 16, 2017.

  1. Chamski

    Chamski New Member

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    No electronics experience here, so hopefully someone can help. Large well insulated home currently has doorbell (just the doorbell switch at the front door) that when pressed connects 12VDC to a truck horn (there is currently no 24AC transformer or other typical doorbell components as part of the setup). Home owner has a Ring doorbell that they would like to install, but when the button on the Ring doorbell is pressed, they want it to cause the 12VDC truck horn to sound for some specified period of time (e.g., 3 seconds, 5 seconds, etc.). I don't know how many amps at 12VDC the truck horns draw, but suspect it is a few. I have purchased a doorbell transformer so that it can be connected to the Ring doorbell and supply the 8-24V AC to keep it charged. Originally purchased FC-32 relay thinking it might help, but doesn't appear to be the right relay for what I'm trying to do. Also purchased a wirewound resistor based on article at
    https://support.ring.com/hc/en-us/a...-Transformer-Without-a-Pre-existing-Doorbell- so that Ring doorbell could be charged by doorbell transformer without having other doorbell components.

    What I'm struggling with is how to get the press of the button on the Ring doorbell 12-24VAC to trigger a relay with a timer so that the 12VDC truck horn sounds for the specified period of time. Looking online, I think the ELK 930 Doorbell Detector might help, but not sure I understand what an "Open Collector" is and how to connect up the "Open Collector" somehow with a relay that has a timer and that can control the 12VDC truck horn.

    Any suggestions for the best components to use and installation instructions would be much appreciated.

    Thank you!
    Cal
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    What supplies the 12Vdc to the existing truck horn?
    Is there a relay between the door switch and the horn? (Typical door bell switches are not rated for much current)
    Where is the truck horn located? In the house? Will it be moved?
    Where is the new doorbell sounder located? Near the existing truck horn and its power supply?

    Frankly, the cleanest approach would be to convert the house, using the existing door switch, the new door bell sounder, and the new 24Vac transformer to a conventional 24Vac loop.

    Once that is working, then add a 24Vac relay whose coil is wired in parallel with the sounder. Then use the new relay's contact to drive a secondary 12Vdc loop that includes the truck horn, its existing 12Vdc power supply, and a new timer module, which you can likely find ready-made on Flea-Bay.
     
    Last edited: Sep 16, 2017
  3. Chamski

    Chamski New Member

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    Thank you for responding. Here the answers to your questions:

    What supplies the 12Vdc to the existing truck horn?
    A 12 volt car battery that has a trickle charger connected to it

    Is there a relay between the door switch and the horn? (Typical door bell switches are not rated for much current)
    As far as I know, there currently is no relay between the door switch and the horn. When the doorbell button (switch) is pressed, it closes the circuit so 12 VDC powers the truck horn.

    Where is the truck horn located?
    In the elevator shaft of the house.

    In the house? Yes

    Will it be moved? No

    Where is the new doorbell sounder located? There won't be a new doorbell sounder added. We're basically just replacing the current conventional doorbell button (switch) with the Ring video doorbell. In addition to the functionality available in the Ring doorbell, the homeowner also wants a press of the button on the Ring doorbell to sound the truck horn.

    Near the existing truck horn and its power supply?
    While the truck horn is remotely located in the elevator shaft, the 12VDC power supply for the truck horn and the doorbell button are all easily accessible.

    Frankly, the cleanest approach would be to convert the house, using the existing door switch, the new door bell sounder, and the new 24Vac transformer to a conventional 24Vac loop. Once that is working, then add a 24Vac relay whose coil is wired in parallel with the sounder. Then use the new relay's contact to drive a secondary 12Vdc loop that includes the truck horn, its existing 12Vdc power supply, and a new timer module, which you can likely find ready-made on Flea-Bay.
    Yes, I think I understand your suggestion here, but one point of clarification is that I'm not adding a new door bell sounder. I'm only trying to add the Ring video doorbell button. I think the part I'm not 100% sure about is the 24VAC loop. As far as I can tell, there is a closed 24VAC circuit with the Ring video doorbell connected and even when the button on the Ring video doorbell is not being pressed. I'm concluding this because the Ring video doorbell has a small battery in it and this battery is designed to be charged from the 24 VAC all the time. So what I can't figure out it is how to trigger the relay since the 24VAC circuit is always closed. The ELK 930 Doorbell Detector product seems like it is designed to somehow detect a change on the 24 VAC loop when the doorbell button is pressed. When it detects this change, then the ELK 930 apparently triggers an open collector. I just don't understand how to use the open collector to trigger a relay. Sorry in advance if I'm missing something important in all this.
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I honestly do not know what a "Ring video doorbell" is? Can you post a link to its datasheet?

    Likewise, the "ELK 930 Doorbell Detector"
     
  6. Chamski

    Chamski New Member

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  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    You can use the tags [quote=]quoted post[/quote] to quote somebody's post.

    A little explanation:

    The technique is called "power stealing". It's used in thermostats because older ones didn't have a common wire. Their suggested (no doorbell) and resistor, means the Ring doorbell sees a current limited by 25 ohms supply when the button is NOT PRESSED. It has to have it's own power for the duration of the press. One method is a "supercap" or a big capacitor.

    16 VAC is not a common relay coil value. It is for a doorbell. It's good that the ring doorbell operates to 24 V. You almost never get 24 VAC from a 24 VAC transformer. It's usually higher. Not sure what the resistance of a typical door chime is. But, it's the combination of that coil resistance that keeps things happy. It must be low enough, but not less than about 25 ohms. It must be high enough,, so the Ring doorbell can "charge" as you put it.

    I want to bring up a 12 VDC to 24 VAC inverter. https://www.powerstream.com/inv-12dc-24vac.htm This is the only one I know of. It's likely not appropriate for anything..

    You can probably get the desired effect with this http://interfacesolutions.uk.com/product/ac-dc-relay/ from the UK.

    You can test, by hooking the Ring doorbell up using the 25 ohm resistor and the conventional doorbell power supply. Put a 360 ohm resistor across the back terminals.
    measure the voltage when the doorbell is not pressed and when the doorbell is pressed and see about how long the activation lasts. If that test gives me the right numbers, the system should work.

    The voltage across the 25 ohm resistor would be useful too pressed and unpressed. The Ring doorbell MAY already limit the amount of on time. This can change the design of the timer related stuff.

    If would give you a contact closure that needs to switch 10 mA (typical) to "clean the contacts"

    The general problem with the proposed idea, is that it draws a few mA all the time.

    This gets you a contact that can't switch the horn directly.

    16 VAC coils on relays are hard to come by. Detecting 16 VAC is less difficult.

    In the long run, the car battery should probably go. An option is here: https://www.powerstream.com/low-noise-high-power.htm Measuring the horn current could help select this too.

    In any event, the automotive relay http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-0-332-209-150-/26-534B has been tried and true for driving the horn. Sockets are available too.
     
    Last edited: Sep 17, 2017
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  9. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I have to go, but I reached out to "Ring".

    The contacts are protected with a 1A fuse. Trickle charge is on the oder of 40 mA or 10% of C (Battery capacity). The "contacts" are closed for as long as the button is pushed.

    Waiting on switching element and voltage drop.

    The OP/TS can measure that with the resistor in place.

    The info will make sense to Mike.
     
    Last edited: Sep 17, 2017
  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I can't think (migraine) right now, so I need to sit on it for a while. The puzzle pieces are not going together easily.
    As for the ELK, it needs 900 mA or more to detect. The fuse is rated for 1A. and 24 V/25 ohms is 1 Amp. Not a good safety margin. With a real door bell there's inductance which can push the threshold over 1 A easily. Not so, with a resistor.

    There's a few other things up my sleave too.
     
  11. Chamski

    Chamski New Member

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    Hi KISS,

    I've been doing some reading tonight and it sounds like the ELK 930 might work best if I actually bought a cheap doorbell and had it connected to the 24VAC loop as well instead of trying to use the 25 ohm resistor. From what others are saying, with a cheap mechanical doorbell ringer in place, when the button on the ring video doorbell is pressed, it should be detected by the ELK 930. Since I already have an FC-32 relay with timer that I'm pretty sure can be used to turn on the truck horn for a specified period of time, I think I just need to figure out how to get the open collector on the ELK 930 to trigger a relay. When this relay is closed, it will trigger the FC-32 relay.

    Thanks,
    Cal
     
  12. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I basically agree with you. It may keep everyone happy including the next guy that works on it. Maybe? Most doorbells are 16 VAC.

    The fact that the button is activating a solenoid nearly guarantees it will work. A resistor has too much flakeyness.

    ==

    I did not look at your timer, nor the ELK in great detail yet.
     
  13. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    If this https://electronics.stackexchange.com/questions/186499/how-to-wire-this-delay-relay-switch is correct with the FC-32. The BIG disadvantage would be that holding the ring doorbell will continue blasting the horn and I don't think you want that.

    You need a non-retrigerable delay on make behavior. The timing interval must complete before a new one can begin.

    I need to try to explain Open collector. Think of it as a contact closure to ground with a drop of about 0.6 V or less. The ELK can support up to 40 mA. So, you may want a contact closure to active the non-retrigerable timer.

    ANY relay used in a DC system should have a reverse biased diode across the coil. This prevents damage to the drivers. So, with the ELK a small relay with one terminal to +12 and the other to the output makes use of the Open collector. A protection diode is added across the coil with the band of the diode to +12. This relay cannot draw more than 40 mA.

    Depending on the timer, you might be able to get away with using a resistor.

    there is a construction technique used in the industry which I'l call DIN rail construction.

    [​IMG]

    All the components mount on a rail and the grey stuff is called wiring duct. It's like an electrical erector set. The case is usually flange mounted on the wall and has a 1/4" aluminum plate at the bottom. A few tapped holes mounts the rail. The grey stuff is wiring duct and can have a cover. I like using 18 AWG with miniml stranding.

    In this case all of the outside world connections are at the bottom. Note the electrical penetrations at the bottom as well. it's like an electrical erector set.

    Here https://www.asi-ez.com/ is a company that deals with higher volumes of th terminals, but it gives you an idea of what you can do.

    i really haven;t found a good construction resource yet. There are no end stops on that picture.
    The bottom row, should start out a as an end stop, terminal block (x10), and end plate and an end stop. terminal blocks have an open end and the last one in a group gets a cover

    if you need to mount your own stuff, here's http://www.winford.com/products/cat_din.php a good resource.

    SnapTrack is also not bad - http://www.farnell.com/datasheets/1537145.pdf

    So, for your timer thing, you can use some spacers and the DIN rail clips on Winford or a piece of snap track and a few spacers. With Winford, you can mount a piece of acrylic on the brackets and then the circuit board with spacers.

    The case and power supply always kill you.
     
  14. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The bell would have to draw at least 900mA for the ELK as is to work. However, the ELK could be modified (by increasing the 2.4Ω resistor value) to sense a bell which drew less current. Bear in mind that the ELK open-collector output current is rated at only 40mA, which may not be enough for some relay coils.
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    alec_t Remember the current in an inductor can't change instantaneously, so an inductance of a bell should create the "blip" or briefly exceed 900 mA.
     
  16. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Depends on the type of bell. Electronic ones (as distinct from the old solenoid-driven ones) probably don't have significant inductance.
     

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