The Raspberry Pi Powered Speaking Doorbell – Part 2: Kodi Camera Overlay

In Part 1, we looked at building a simple input circuit to electrically isolate and protect our Raspberry Pi from damage when connecting it to our doorbell switch. Next, we’ll look at displaying a camera overlay directly in Kodi / XBMC and triggering the display from a Python script.

IP cameras have become really cheap and easy to come by, giving us many options to integrate video into our home automation systems. The front door is a great place to install a camera!


The Digital Lifestyle has a very good write up on how to install and configure an add-on to display the camera overlay (especially if you have more than one camera) directly in Kodi itself.

We can then use some Python code to trigger the add-on using Kodi’s API.

Prerequisites: In Kodi, make sure “Allow control of Kodi via HTTP” is set to ON in Settings -> Services -> Webserver.

I wrote a small XBMC / Kodi client to make it easier to make calls to the API. Here is the method for triggering an add-on:

    def execute_addon(self, addon_id):
        payload = self._get_payload("Addons.ExecuteAddon",
{'addonid': addon_id})

And here is the code for instantiating the client and executing the add-on:

xbmc_client = xbmc.XbmcClient(host, port)

On line 1, we instantiate the XBMC client by specifying the host and port. The port is configured in Kodi’s Settings -> Services -> Webserver -> Port.

The only parameter we are passing to the execute_addon method is the ID of the add-on we wish to run. Set it to the add-on ID that you specified in the addon.xml file.

That’s it. Next, we’ll look at how to build a text to speech server using Tornado.

The Raspberry Pi Powered Speaking Doorbell – Part 1: The Input Circuit

<< Previous post – The Raspberry Pi Powered Speaking Doorbell – Video

The first step of building the Raspberry Pi-powered speaking doorbell is building a simple input circuit. The purpose of the input circuit is to protect the Pi from damage by electrically isolating the doorbell and its power supply from the Raspberry Pi itself.

The circuit design and a full description of how it works can be found here. The power supply I used is rated at 12V, but the LTV-847 optocoupler used in the design copes just fine with an input voltage of 12V. It is a 4 channel optocoupler, so you can read 4 different inputs using the same optocoupler. I like using veroboard / stripboard for my circuits because the soldered connections are a bit more robust than a breadboard setup.

Input Circuit

Input Circuit – Top view

On the left are the 2 single-core cables that are connected to my doorbell and its 12V power supply. The + (anode) of the 12V power supply is wired to my doorbell button which in turn is connected to the input circuit (top left cable). The bottom-left cable on the input circuit is then connected to the – (cathode) of the power supply.

On the right-hand side, you’ll notice a ribbon cable. I have a model B Raspberry Pi, which has a 26 pin P1 header. I bought a 26pin IDC crimp connector and some ribbon cable, which fits perfectly on the P1 header.


The red cable indicates Pin 1 on the Raspberry Pi, so in the input circuit picture, the top right cable is connected to the 22nd cable of the ribbon cable (which corresponds to pin 22 on the Raspberry Pi) and the bottom-right cable is connected to the 20th cable (pin 20 on the Pi).


(Diagram from

As you can see from the pin mapping diagram, pin 22 is GPIO 25 and pin 20 is Ground.

Input Circuit - Bottom view

Input Circuit – Bottom view

You’ll notice on the bottom view of the input circuit that the tracks on the stripboard is scratched off between the input and output sides of the optocoupler. It is a good idea to test with a multimeter to make sure there is no continuity when measuring on either side of the “break” in the track to be sure that the connection is properly broken.

If you are like me and your soldering skills are not great, I would recommend testing the circuit before connecting it to your Pi. Get a friend to press your doorbell button while you measure continuity on the output side of the optocoupler – when the doorbell is pressed, the output side should be closed. When it is not pressed, it should be open.

I also like to test to make sure there is no continuity between consecutive tracks on the stripboard to make sure I didn’t accidentally solder a connection between tracks.

In the next post – how to display the camera overlay in Kodi.

The Raspberry Pi Powered Speaking Doorbell

Doorbells are so last century. While watching an episode of the futuristic, sci-fi thriller Extant, I realized that the future of the doorbell is now! In the episode, a voice, presumably the product of some smart home automation system, announces that a visitor is at the front door. Easily achievable with a Raspberry Pi and some Python code!



Our future-is-now speaking doorbell uses a Raspberry Pi with a simple input circuit wired to our existing doorbell button. When a visitor presses the doorbell, the Raspberry Pi does a number of things: Firstly, it pauses the currently playing video and displays an on-screen message on both of our media center PC’s. Then, using a text-to-speech converter on the living room media PC, it announces that there is a visitor at the front door. And finally, an on-screen video from an IP camera mounted at the front door is displayed on both TV’s.

>> Next post – Part 1: The Input Circuit