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I'm really not used to Arduino and I would like to know if it would be possible to tweak my doorbell, most specifically the bell itself, to embed a small arduino that would be able to send a notification "somewhere" (well, if it can connect to wifi and send an HTTP request I can handle the rest).

I'm guessing that there will be electricity in the bell itself (to.. ring it I guess) so I could use that to power the Arduino.

My goal is definitelly not to create a "smart" doorbell but to upgrade a tiny bit the one we already have. My biggest problem is that when I am in the office, I can barely hear it and if I turn music on, it becomes impossible.

Before launching myself in this, I'd like to know if it is at all possible. I can (try to) provide more information if needed.

Thanks.

EDIT: I'm guessing that the bell rings when it gets an electric signal when the button at the door is pressed. My goal would be to hook up to that signal to get the arduino to send an HTTP request. Now, my arduino knowledge is very limited and I'd like to see if anyone could give a tiny bit of guidance on how to proceed (which one, which module, ...)

EDIT2: As requested, here is a picture of the bell part: [![bell][1]][1]

In the center there is a copper coil so I would guess that when someone presses the button, the little hammer (pointy thing going up) hits the 2 metal plates (up and down). I could also see that there is a third cable (purple) hidden behind that is not currently used but I have no clue what it is for or if there is power at all on this thing...

EDIT3: I realized that I have a Friedland D780 on the fuse box (so right next to all the power I can need for an Arduino). It is unclear if I could get the pulse from here though. Anyone?

I can't upload a picture with my phone but I'll add it ASAP...

[1]: https://i.stack.imgur.com/pdgbs.jpgenter image description hereenter image description here

  • In order to help some clue as to what your doorbell is would be helpful. I have a system where I modified a standard doorbell's powered push button to send a signal via an ESP01 and WiFi to MQTT running on a Raspberry Pi but the permutations and methods are many. – Bra1n Apr 30 at 11:28
  • I'm going to try and get more informations and photos – Georges Legros Apr 30 at 11:28
  • I added a photo in the question as requested. – Georges Legros Apr 30 at 13:49
  • Most doorbells use AC with a voltage of 8-24 Volt. This voltage is created by a transformer. Where I live this transformer is located in the fuseboard closet. This voltage goes to the bell, but is interrupted by the bell-button, until it's pressed. So to power your device you'd have to rectify the AC to DC, and then regulate the voltage to 5Volt of 3.3Volt. The problem is that you only get power while the button is pressed, so you'd need a way to store enough energy to make your HTTP request. – Gerben Apr 30 at 14:56
  • If you have a multimeter, I'd measure the voltage between the purple wire and the white/blue wires. – Gerben Apr 30 at 14:57
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Many (most?) household doorbell systems in the US are powered by a simple transformer that converts 120V AC household electric supply to a lower voltage AC. Often 16V AC or 24V AC.

The coil and hammer form a device called a solenoid. When the coil is energized, the hammer (often also called a plunger) is forced in one direction, either up (against gravity) or against a return spring, striking one of the plates. When power is removed, gravity or the return spring pull the plunger back to the rest position, striking the other plate, forming the familiar ding-dong sound.

Power is applied or removed extremely simply -- by the momentary, normally-open pushbutton at your door. When you press the button, the solenoid is energized, and when you release it, the device returns to the normal state.

With regard to powering your Arduino, it is important to understand the difference between AC and DC power. The Arduino requires DC (direct-current) of either a regulated 5V DC into the 5V pin, or unregulated 7-12V DC into the VIN pin, or the regulated 5V DC from a USB device.

I don't know your level of electricity understanding, but there exists quite a bit of information on the difference between AC and DC power. Suffice it to say, you would need some additional circuit to rectify and filter and regulate the 16-24V AC into something between 5V and 12V DC.

Then, there is the issue of the loss of a good power tap while the button is pressed. If you measure the voltage across the contacts of the pushbutton while it is not pressed, you will likely find the full 16V AC or 24V AC, but if you measure those contacts while the button is pressed, you will read 0V AC. This means that tapping off of the pushbutton wires is not a good way to power a device that needs to remain on while reacting to the button press. Whether or not you could tap power off of the solenoid terminals is dependent on the voltage drop across the coil, and still you have the issue to convert the AC to DC at the proper voltage.

If this doorbell is near the ceiling, you will likely find the transformer mounted in the attic space above the ceiling near the doorbell (if there is attic space -- depending on your specific setup). If there is a power outlet in this attic space, you could plug in a good quality AC-DC 5V adapter there to power the Arduino in the attic. The Arduino will need to remain electrically isolated from the doorbell circuit. To detect the pushbutton press, you could use a current transformer measuring the current flow through either of the 16V AC wires coming off of the transformer (measure with one of the the analog inputs of the Arduino), or with an Opto-isolator, with the transmitter connected to the doorbell circuit in a way that delivers a small current (10mA or so normally) to the transmitter side of the opto-isolator, and read the receiver side with a digital input pin on the Arduino.

Unfortunately, interfacing with a doorbell that uses AC power will require some good planning and evaluation of your doorbell system and how much additional circuitry you are willing to apply.

If you aren't careful, working near the transformer can be very dangerous to your life. Working with 16-24V AC will not be as dangerous to your life, but can easily damage the Arduino beyond repair in the flash of an eye. Take great care.

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Much as I like Arduinos, it might be easier to just run a wire from your current doorbell to your office and add a 2nd doorbell, or a piezo buzzer that will run on AC. As others have said doorbells in the US are usually powered by AC, and that power is only available while the doorbell is actually ringing. You would need a constant source of power in order to drive your Arduino long enough to connect to a network and send a signal.

You might be able to build a circuit that rectified the AC power to DC and charged a capacitor, then used that capacitor to drive a DC power supply to the Arduino. The capacitor might hold a charge long enough for the Arduino to make a network connection and send a signal, but you'd need a fair amount of electronics knowledge to make that work.

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    Some of the piezo buzzers I've seen will run with a wide range of voltages, from 6 to 18. You could put a bridge rectifier on the AC in from the doorbell, then a simple voltage divider to drop the voltage from 24V to 12. Alternately you could use a 2:1 transformer to step down the 24VAC to 12VAC, then a bridge rectifier, and then the piezo buzzer. – Duncan C May 1 at 0:57
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If I could offer a different approach -- to maintain isolation between the doorbell AC and an Arduino, you could have the separately powered Arduino 'listen' for the sound of the gong. A cheap mic feeding an analog input does the trick. Mount it in the same housing to isolate it from household and other noises, or maybe tune it to respond to a narrow range of frequencies.

There are other non-contact, non-wired possibilities too -- sense the motion of the solenoid, or its electrical field, etc.

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