Wired Doorbell - Connection to Konnect

I connected my traditional wired AC powered doorbell to my Konnect system through a circuit that creates a 3.3V DC signal.  I will attach a picture of my circuit and setup.  Right now I only have the front door doorbell connected. 

My question has to do with selecting the best type of zone sensor for a doorbell.  Right now I am using the open/close switch but I am wondering if anyone has a better solution.  I would prefer to have an icon that is similar to the smoke detector, one which is not colored until the button is pressed.  If anyone has any advice please let me know.  I am brand new to using SmartThings.  I created an automation that pushes a notification and text to alert me that someone is at the front door.  

I am also going to implement my mailbox soon.  I installed a proximity sensor which uses a Hall effect sensor and a magnet.  The sensor is hard wired and I buried the wire from the mailbox to my house.  

Here are a few pictures of my mailbox sensor.  

Opps, I just noticed a mistake in my circuit drawing.  Here is the correct depiction.  The circuit connects between the switch and the transformer, not to both switches.  


Based on the second schematic you are grounding the Front doorbell F signal.
I follow the pink line from the chime F and as I move to the right, below the line is a ground icon.

Wow this is a great idea. Can you explain to me why you can’t take the two wires emerging from the doorbell and connect it as a door sensor whose default state is open? When the button is pressed it would close the circuit and be the equivalent of a door close sensor that doesn’t require any power at all.

If you connect your wired doorbell to your Konnected board like you would a door contact sensor you will damage it.  A wired doorbell is an AC circuit running somewhere between 14 to 36 volts.  In order to utilize this with your Konnected board you will need a circuit that converts the AC circuit into a 3.3 volt DC circuit.  The circuit I show above works but its not the only way and I would suggest looking into a circuit that isolates your Konnected board from the AC circuit all together.  An opto-isolator circuit would be a better choice.  In the future I might replace this circuit with one of those designs.   

I did not design the circuit above but I built it and it works.  The circuit works by rectifying the AC signal into a half-wave DC signal.  The signal then goes through a smoothing capacitor and a voltage divider to drop the voltage.  This low level signal then drives a transistor which is acting as a switch connected to the Konnected board.  

I am not an electrical engineer and I make no claim to the safety of this circuit.  I am sure certain conditions could damage your board but it works well for me.  Perhaps someone else wants to chime in with a safer or better design.  I am sure their are many ways you could do this.     

I'm a newbie here and I was also interested in hooking up my wired door bell.  Would a 24VAC relay work?  Simply when the doorbell is pressed it would apply power to the relay and the relay would in turn open or close a set of contacts?

Brian, were you able to make this work with a relay? I was also thinking a buck converter could work (basically what Christopher has done from scratch above). I’ve seen a couple on Amazon that could take the 16-24V AC from the doorbell and convert to the 3.3V DC signal needed for the Konnected board. Being a newbie as well, I’m not sure it’d be sensitive enough to capture the quick press of the doorbell.

Sam, I never got to try it, I kinda forgot about this project.  I also saw that you could use a wired magnetic door sensor inside the door chime to trip it.  If I get then motivation to try something I'll keep this post updated.

I redesigned my circuit to use a 4N25 optocoupler.  The benefit of this design is that the AC doorbell circuit is completely isolated from the DC circuit that connects to the ESP8266 micrcontroller.  

This circuit is very easy to build.  For the doorbell circuit you only need a 4N25 optocoupler, four 1N4004 diodes (or similar) and a 1K resistor.  How you connect the other side of the 4N25 is up to you but it could be as simple as a 10K resistor.  

My doorbell transformer puts out 22 volts AC.  I rectified the AC into DC using four 1N4004 diodes.  That dropped the voltage to 20.5 volts DC.  The DC voltage then needed to be filtered to remove the ripples.  I experimented with several values and found a 100 uF 35v capacitor to work well.  Larger value capacitors held a charge too long so when the doorbell was rung the 4N25 would not detect the voltage drop.  Smaller values did not smooth out the DC ripple.  You may have to experiment a little for your setup.  I calculated that a 1K resistor would keep the current of the internal 4N25 infrared LED at around 20 mA, well within the 10 - 60 mA specifications in the data sheet.  You would need to adjust this based on the voltage of your AC doorbell transformer.    

You connected the AC portion of the circuit to the doorbell chime.  You will have to choose the front door or the back door portion of the chime.  If you want both doors you will have to build two circuits.   The output of the 4N25 will connect to your ESP8266.  

I am not attaching a video clip of the circuit in operation but this is how it works.  When the doorbell is idle the Red LED light on my protoboard is illuminated.  When the doorbell is rung, the LED light does out.  So at idle the output is Logic High and when rung is at Logic Low.  

I hope this helps anyone trying to connect a traditional hard wired doorbell.  

Chris, thanks for  your description and explanation. I have very little experience with circuitry, so I opted for something more simple (in my mind). I purchased a current sensor from Amazon for $18 (also available for $10 on Aliexpress.com) and was pleased to see it works! My transformer output is 20v AC and the sensor even detects a short button press. I had previously tried the reed switch next to the solenoid, but was never able to get that to work. 

Current Sensing Switch, Normally Open Current Sensing Switch Adjustable AC 0.2A-30A (SZC23-NO-AL-CH)


I want to say thanks to both Christopher and Sam for the info here.  I've tried a couple different solutions trying to get reliable sensing of a traditional doorbell button press.  I gave Sam's 'Current Sensor' a shot and it works beautifully!  I adjusted the dial a bit and now it senses even the quickest button push.  It also just barely fits inside a 2 gang box w/ the transformer.