Hi. I installed a sonoff sv (after converting it into a dry switch) inside my intercom to be able to control the front door buzzer remotely. This works great with home assistant too, using IFTTT (hopefully I will manage to install tasmota on the sonoff one of these days, so I won’t need IFTTT anymore). Anyway, now I have a cool button on my dashboard and I can open the door of my building remotely… i.e. I don’t need to have the key with me anymore (I already installed a Sherlock on my apartment door, so no key for that one either)!
As you can see in the picture it fits well inside the intercom too, which makes it very neat! Except… that white cable you see going in there. That’s to bring 5V power to power up the sonoff sv. I was hoping that I would be able to find power inside the intercom but either there isn’t any or I’m doing something wrong.
I know this isn’t exactly a HA question, but I was hoping somebody might have an idea. This is the connection diagram (the 1st diagram in this link, type 8875). I used my multimeter and I can detect 5V voltage between some of the cables coming in the intercom. When I connect the sonoff to these cables though it doesn’t power up and when I put the multimeter again there, while the sonoff is connected, the voltage drops to 1V. Is there is a solution to this problem?
There is this solution called Nello and that one somehow gets power from the intercom and works, so i was hoping I could do the same. Nello also has a rechargable battery in it. Could this be how it works? Somehow the battery charges with low voltage and then is able to power up?
Actually did the exact same thing with mine a week ago! Don’t think you can solve the power issue though I got a 12v transformer from banggood small enough to fit in the junction box behind mine https://banggood.app.link/e4mo3Pml3V
Hello, I have the same goal that you have (make my intercom smart with the help of Home Assistant) and I have a Sonoff SV flashed with Tasmota. Can you please explain me how did you connect your Sonoff to the intercom and why did you convert it to a dry switch?
Thank you for your help
Your intercom buzzer works by shortcircuiting (connecting) two of the connectors available. This is what the button does when you press it. To find which of the two connectors, you need to check your manual. If you don’t have your manual, find some kind of model number printed on the circuit bord or plastic cover and google it (in my case I googled elvox 8875). If you find the pair you need to shortcircuit, you connect them to the two connectors of the sonoff. You need to convert it to a dry switch, because you want to use sonoff as a switch (connect the two ends of the intercom).
It worked! I found out that my Intercom (a SIEDLE HT 511-01) opens the door when the port I and C are shortcircuited, so i made exactly as you said:
convert the Sonoff SV to a dry switch
shortcirquit the output port of the Sonoff SV
connect the input of the Sonoff SV to port I and C
power up the Sonoff SV
through the web interface when I toggle the Sonoff to ON it opens the door
Thank you very much!
Now I would love to interface my doorbell (which gets 11V AC when the doorbell rings) with Home Assistant in order to get a notification (ideally a push notification on my android phone) when someone rings the bell.
Do you have an idea how to do that?
So far I used an external power supply (I used an old USB phone charger) but I think I will try to power it with batteries and using it in Dynamic Sleep Mode to see how long a battery would last. How did you power it up?
I did the same. I don’t think that you will have much luck with battery, since Sonoff uses WiFi. Had it been bluetooth, maybe. Unless you find a way to charge the battery with the low voltage power supply of the intercom. I still do not know, but I guess this is how Nello does it.
Hello everybody, I recently read about the 1% law and you are the proof science is awesome.
I have the same issue/need of using a Sonoff SV, already converted as Dry Contact after following the link to the youtube video at first post, and went through the steps @lordslash was so kind to provide.
But there is something that I can not understand: 1) The guy in the video removes the 2 resistors near the IN+ and IN-, then shortcircuits IN+ and IN- with a wire.
In the image that @papadi posted, I can clearly see that the resistors are still there and there is no wire/short circuit on IN+ and IN-.
Also, @lordslash wrote:
shortcirquit the output port of the Sonoff SV
connect the input of the Sonoff SV to port I and C
Why shortcircuiting the Output? Why connecting I and C to the INput?
I can’t follow you you both guys have done something else compared to the guy of the video. Can you please clarify?
2) If instead of opening the door I want it to capture the Buzzer/speaker when it rings, can you maybe give me advices on how to proceed? When the buzzers rings (circuit closed), Tasmota should be able to capture this signal and to send a mqtt message to my broker (done already, i have other sonoff in use), therefore update the Switch status to ON. When the buzzer stops ringing, the switch to go back to OFF and so the mqtt message.
So basically, it is not me to push TOGGLE rather Tasmota to update the status accordingly.
Can you maybe tell me how do I achieve that please? I’m kind of lost
Look closer . The resistors aren’t there. And I guess I did the shortcircuit of the contacts on the other side of the board. I don’t remember, to be honest.
Interesting, but I cannot help. I guess you will need to squeeze two sonoff in there though. Perhaps sonoff isn’t the way to go in this case.
Hi @papadi, thank you for your answer!
About the Dry Contact I have no other questions, it works actually so that’s great! And looking at the pic a bit closer I can see that the resistors are not there. Thanks for explaining it.
Point 2 instead is still a bit unknown to me. I have the feeling that using Tasmota it works, but I miss the “how”. I found this git project: https://github.com/w4ilun/ESP8266-Intercom (and complimented the guy for his job) that shows that connecting 1 relay to the buzzer it works.
I went through the code but haven’t still understood how the same code would be applied on Tasmota. Perhaps some Tasmota rule, or something.
Of course I could just use his code as it is. I only miss the relay board but that’s easy to find. On the other side, Tasmota connects great to my HA and mqtt works perfectly. I would like to remain on this system.
I have instead never used Sonoff’s stock firmware.
Follow the doc here: https://tasmota.github.io/docs/Getting-Started/
I have followed several method for flashing it on ESP8266 chips, the easier could be using a USB to TTL adapter but this requires access to the flashing Pins on the device. The Sonoff SV (and some others) have them exposed.
Make sure you set the adapter to 3.3v. For this case, buy a USB-TTL adapter that supports changing the output voltage.
In short:
Connect the USB-TTL to your pc (windows or linux doesn’t matter, I use them both)
Connect the GND of the USB-TTL to the GND of the Sonoff; The VCC to VCC, RX to TX and TX to RX.
Open whatever software you prefer, the newer is “Tasmotizer”.
Select the firmware, select the COM port and flash it.
Once flashed, tasmota is reachable at 192.168.4.1. Put your pc on that network Connect to the open WiFi network that Tasmota has just created and once you open the webpage you can give your SSID to the tasmota. It will reboot and then connect to your Wifi.
Some other devices (Smart plugs from Tuya for example) have very limited access to those pins and sometimes you just can’t.
For those cases, there is tuya-convert: https://github.com/ct-Open-Source/tuya-convert
It flashes the firmware over-the-air faking an update server. It doesn’t always work, especially if the device is patched.
Other timess it may fail not because of the patched firmware but due to strict system requirements and branches/forks of the same repo.
Now i can’t find it, but there was a repo that managed to flash my smart plugs when the original couldn’t.
You need to remove the board from the frame and see where the pins behind the door button (see picture below) lead to. Those are the wires you are looking for. But I guess it’s these L- and L+ pins, because the wires on the left go to the speakerphone.
I got a 12v transformer from banggood small enough to fit in the junction box behind mine 
you both guys have done something else compared to the guy of the video. Can you please clarify?
. The resistors aren’t there. And I guess I did the shortcircuit of the contacts on the other side of the board. I don’t remember, to be honest.
