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Calculating Resistor Value for Video Doorbell / Home Intercom Mashup

Discussion in 'Power Electronics' started by jayvee, Jan 22, 2021.

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  1. jayvee


    Jan 22, 2021
    Description of Project:

    I am just getting started learning about electronics. I have a solid background of residential electrical systems, but that is so simple compared to what I’m starting to encounter while dabbling with electronics. I’m sure I’ll use incorrect terminology in this post and I don’t want to pretend that I know any more than I do – which is almost nothing – especially when it comes to calculating sizes of resistors or other components.

    I am currently trying to incorporate a first generation Ring Video Doorbell into my Mom’s existing whole-house intercom/doorbell system. The concept is pretty simple and understandable even for me, but I’ve run into a technical issue that is a great opportunity for me to broaden my understanding.

    The existing intercom system incorporates an electronic chime module. When the existing doorbell button is pressed, a chime is played throughout all of the intercom units throughout the home. This doorbell circuit has its own power supply, and like most doorbells, pressing the existing button simply connects two contacts together.

    I cannot simply replace the existing doorbell with the Ring Video doorbell because the Ring Video doorbell has different power requirements than the intercom system and the intercom system has its own internal logic that is not a simple circuit I can count on for constant power.

    The plan is to use a 24VAC transformer to power the Ring Video Doorbell. Ring provides a drawing of how to wire a simple circuit that includes a mechanical doorbell inside the house. I’ve taken that drawing and added onto it to explain the plan. In my modified drawing, I have replaced the mechanical doorbell with a relay. When you push the Ring Doorbell button, the relay output terminals will close. The outputs of this relay will replace the existing push button doorbell.

    Drawing 1 No Resistor.jpg

    I’ve put together a test setup. On the output side of the relay, I have an LED light powered by a benchtop power supply. Once the relay closes, the LED lights up. This proves that I will be able to replicate the push button functionality of the existing doorbell. Basically, pushing the ring doorbell, will cause the intercom system to think that the old push button has been pushed by someone.

    Test Setup Ring Doorbell.jpg

    From the beginning, I was successful in getting the relay to close when pushing the Ring Video Doorbell button. But early on it became clear that there was a problem. The relay was clicking every half second or so – when the doorbell button was not being pushed. If I had hooked this up to my mom’s house, her intercom system would have constantly been sounding the doorbell through her house. The Ring Video Doorbell is not a simple mechanical switch like the existing doorbell is. Even when the button is not being pressed, current is flowing on the Ring Circuit.

    I saw a video on youtube where a guy had a very similar problem. His mechanical doorbell was humming and looked to be on the verge of ding-donging at all times when connected to the Ring. In his video, he simply connected a 10 ohm resistor to the terminals of his doorbell (Front and Trans terminals). His problem stopped. The doorbell stopped humming, and the bell stopped vibrating.

    I dug through some spare parts that I have and turned up a 220 ohm resistor. There was no math involved in this decision. I just wanted to see if it would have an effect on my chattering relay. As soon as the resistor was placed under my screw terminals of my prototype board (screw terminals A and B in my drawings), everything seemed to be working perfectly. I’ll include a section with voltage measurements later on in this post, but for now, I had no more nuisance relay action/relay chatter. The LED light on the output side of my relay flashed briefly every time I pressed the ring doorbell button – as was hoped for.

    Prototype Board.jpg

    Drawing 1 No Resistor.jpg
    With No resistor (as seen in Drawing #1), voltage between screw terminals A and B is ~18VAC (when Ring Doorbell button is NOT being pressed)

    When the Ring Doorbell button is pressed, the voltage spikes momentarily to ~27VAC and returns to about ~18VAC when the Ring Doorbell’s process has completed.

    Drawing 2 Parallel Resistor.jpg
    With a 220 ohm resistor placed in parallel (as indicated in Drawing #2), screwed under terminals A and B, voltage between terminals A and B is ~1.8 VAC (when Ring Doorbell button is NOT being pressed)

    When the Ring Doorbell button is pressed with the 220 ohm resistor installed under screws A and B, the voltage spikes momentarily (the spike seems to vary widely (5VAC, 8VAC, 19VAC)), then while the Ring Doorbell is going through it’s process (audible ring, light show, alerting my phone (~15 seconds)) the voltage reads ~0.02VAC. When the process ends, voltage settles back to a steady ~1.8 VAC.

    So here are the questions that I would appreciate being educated on:

    1) Based on the components in my circuit, and the measured voltages I have listed, what size resistor should I be using? (read: which would be safest to use)

    2) Should my resistor be in parallel as shown in drawing #2? …or in series as shown in drawing #3?
    Drawing 3 Series Resistor.jpg

    3) Is a resistor even a logical solution to this problem, or am I misunderstanding to think that the resistor is reducing the current flowing through the relay when idle.

    4) In the future, how can I use the datasheets provided for the bridge rectifier and relay in my circuit to select the correct component without asking people for help.

    5) Sort of related…what are some of you guys using to draw circuits? Any free tools available that you feel are easy to use and produce clear drawings? I did these drawing modifications in MS Word… not as primitive as MS Paint, but still, nothing to be proud of or plan to continue using.

    I hope these questions are appropriate for this forum. I am primarily interested in making sure that this setup is safe for my mom’s house and that I have selected and correctly installed the appropriate component (resistor??) to keep the relay from chattering / nuisance closing of the output terminals. Coming in a close second is my trying to learn how to interpret the datasheets and learn some of the basics of using resistors.

    Thank you all so much for any input, education, or corrections that you’re willing to share with me. Below are some details on the components involved, their datasheets, and the voltage readings I am getting in various configurations.




    Bridge Rectifier:



    I am really interested in understanding how to use the datasheets and general theory to calculate a safe resistor to use in this application. I think it is dumb luck that I selected a value that ended up working. The idea to try a resistor came from a video in which someone used a 10 ohm resistor to keep their mechanical doorbell from humming. Also I don’t know whether the resistor should be placed in parallel or in series.

    This is going to end up installed on my mom’s house, so I need to make sure that I am not creating any fire or other hazards.

    Attached Files:

  2. Bluejets


    Oct 5, 2014
    I'd say your ring video door bell is not what you think it is.
    Instead of providing what you think is the answer/problem, show us all the detail you had to work with from scratch.
  3. Martaine2005


    May 12, 2015
    Resistance is calculated R=V/I.
    (Volts divided by current).
    A resistor in parallel will generally act as a load.
    If your 220Ω resistor does not get warm or hot, it will more than likely be fine.

    jayvee likes this.
  4. jayvee


    Jan 22, 2021
    Thank you, Martin. All seems to be working well after several days connected using that resistor. It hasn't gotten warm. Take care.
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