Hi. I'm looking for some advice on how to complete a small project I've had in mind for a long time. My level of electronics knowledge is basic. I understand for the most part many concepts and can solder fairly well.

I live in a very long apartment and the "buzzer" which people ring from downstairs to get into the building, is all the way on the other side of it. I want to be able to use my phone to release the door to open.

I recently picked up a bunch of these great little sonoff wifi relay devices (https://www.itead.cc/sonoff-wifi-wireless-switch.html) which do all the heavy lifting. All you have to do is attach a 220v device to it and it you can control it via it's app anywhere in the world.

From what I can tell however measuring with my multimeter, pushing the button on the phone unit to release the door solenoid downstairs is accomplished with a small current of 11VAC. Therefore in order to use the sonoff device above, I think all I would need to do is convert the 220v input into 11v output needed. In theory then all I should have to do is solder a small 220vac -> 11vac transformer to a circuit board and then send the output of the sonoff through that, and then the output of that directly into the appropriate leads on the phone terminal. I found this transformer on ali express (https://www.aliexpress.com/item/AC-...815972389.html?spm=2114.search0302.4.2.5jVKrJ)

... I *think*

Am I oversimplifying this? How would I go about this?

Many thanks in advance for your advice.

 

It's possible that all you need to do, is to modify the output switching side of the Sono, more than likely its a relay output, just rewire the contacts to Normally Open Volt free.

 

It's possible that all you need to do, is to modify the output switching side of the Sono, more than likely its a relay output, just rewire the contacts to Normally Open Volt free.

Thanks. I don't really understand what this means though. The sonoff gets 220v from the mains and at some point when I click on a button in the app that controls it, it acts like a switch and lets the voltage and current through. If i rewire something to volt free where do i get the 11vac needed to open the door?

 

You would still need a 11V supply for your door bell, your idea will work with a transformer just as good.

 

You would still need a 11V supply for your door bell, your idea will work with a transformer just as good.

Great. Thanks for that!

 

I believe it is much simpler than that.

You currently have a button on your phone in the apartment that you press to open the door. I think that is what you have stated.

I suspect that this button is just a simple switch and doesn't actually source any current. (it doesn't make sense to me that each unit would be sending the voltage - much cheaper that each apartment just has a switch and voltage is sent from a central point.) You can verify that by disconnecting one of the wires and see where the 11 volts is coming from. I'm pretty sure it's actually 12V that originates at the door unit - 11V because of the voltage drop from the long wire.

So, if it is, indeed, just a simple switch, you just wire the "load" side of the wireless relay across the terminals of the button (ie, wire the relay NO output in parallel with button switch) and it should work. No mods needed to the wireless relay.

By the way, the schematic for that unit is here: https://www.itead.cc/wiki/images/f/ff/Sonoff-Schematic.pdf I couldn't find a datasheet for the specified relay but it looks like a cheap 5V relay with Normally Open contacts only. The 220V noted is because it's power supply is a global one. It will work on 110VAC. The relay contacts appear to be spec'ed to up to 220V and 10A. The sonoff unit doesn't output any power at all.

 

I believe it is much simpler than that.

You currently have a button on your phone in the apartment that you press to open the door. I think that is what you have stated.

I suspect that this button is just a simple switch and doesn't actually source any current. (it doesn't make sense to me that each unit would be sending the voltage - much cheaper that each apartment just has a switch and voltage is sent from a central point.) You can verify that by disconnecting one of the wires and see where the 11 volts is coming from. I'm pretty sure it's actually 12V that originates at the door unit - 11V because of the voltage drop from the long wire.

So, if it is, indeed, just a simple switch, you just wire the "load" side of the wireless relay across the terminals of the button (ie, wire the relay NO output in parallel with button switch) and it should work. No mods needed to the wireless relay.

By the way, the schematic for that unit is here: https://www.itead.cc/wiki/images/f/ff/Sonoff-Schematic.pdf I couldn't find a datasheet for the specified relay but it looks like a cheap 5V relay with Normally Open contacts only. The 220V noted is because it's power supply is a global one. It will work on 110VAC. The relay contacts appear to be spec'ed to up to 220V and 10A. The sonoff unit doesn't output any power at all.

I'm new to electronics so this stuff doesn't come easy to me yet but after some careful inspection I discovered that this is exactly right. The button press simply bridges a connection just like a switch. So I connected one terminal to the input of the relay on the sonoff and the other to the output of the relay and that worked perfectly! Thanks very much for pointing this out. It was in fact super simple.

 

Hello Nuevallorker... I am not an expert on this and I would like to apply the same solution as you. Could You explain it to me step by step? Please....

 

I understood You connected one terminal (One of the two cables from the intercom switch ) to the input of the sonoff and the other cable from the intercom switch to the output of the sonoff. My doubt is what else is required? the 220v which source the sonoff how is connected?

 

I'm new to electronics so this stuff doesn't come easy to me yet but after some careful inspection I discovered that this is exactly right. The button press simply bridges a connection just like a switch. So I connected one terminal to the input of the relay on the sonoff and the other to the output of the relay and that worked perfectly! Thanks very much for pointing this out. It was in fact super simple.

I understood You connected one terminal (One of the two cables from the intercom switch ) to the input of the sonoff and the other cable from the intercom switch to the output of the sonoff. My doubt is what else is required? the 220v which source the sonoff how is connected?

 

This project is not for new people. It will take 3 months for this prototype to be finished. It will.be much better if you use a radio frequency or Bluetooth hc 05 module if the distance suits you.

 

Agreed but the sollution found by nuevallorker seems suitable for an easy project for newbies as me

 

I am happy it worked!

Marry Christmas and happy new year!

 

Same for You. I hope nuevallorker answer the question I asked him in order to solve my doubt

 

I'm new to electronics so this stuff doesn't come easy to me yet but after some careful inspection I discovered that this is exactly right. The button press simply bridges a connection just like a switch. So I connected one terminal to the input of the relay on the sonoff and the other to the output of the relay and that worked perfectly! Thanks very much for pointing this out. It was in fact super simple.

Hello,
I am attempting a similar project with a sonoff. Where does the 220v power supply come in? Or does the sonoff wifi work with just the 11V connection?

A few additional details on what is connected where would be very helpful.

Thanks!