Need help to make two doorbells work simultaneously

Thread Starter

Anomajaya

Joined Jul 11, 2023
59
Hello everyone,

I'm not an expert on electronics. I have an old analogue doorbell that works directly on 230V AC. And there is another Wifi enabled smart video doorbell as well. The basic idea of my project is to make both doorbells ring when either button is pressed. As the video doorbell is very sophisticated for me to hack, I only could take out two wires from the momentary push button of that bell. Basically, I have extended that button and if I short those two wires together, the video doorbell rings. There is a 2.85v (DC) voltage in between both these wires.

I tried to synchronise both systems using two relay modules but failed. I’m attaching the wiring diagram herewith. Once I press the old system switch, it rings both systems. But, when I press the Video doorbell, it does not trigger the 3v relay module and hence the old electric doorbell. Once I press the video doorbell the indicator led in the 3v relay module lights faint and beyond that nothing happens. I know this is very primitive work and please bear with me as I’m no expert on this.

If any of you could help me in this regard, that would be highly appreciated.

Thanks heap.
 

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panic mode

Joined Oct 10, 2011
2,672
remove old button from AC circuit and connect it to button of your new doorbell.
now pressing either of the two buttons should make new doorbell operate.

next add circuit to monitor voltage across the buttons. when it is low, activate relay. wire relay contact to AC circuit where old button was.
 

AnalogKid

Joined Aug 1, 2013
10,944
Are you sure the old doorbell is running directly off the mains, and not off of a low voltage transformer tucked away in the basement rafters somewhere? In the US, these have been a fire code requirement since at least the 1950's

ak
 

MisterBill2

Joined Jan 23, 2018
17,827
The concept of a directly mains powered doorbell is disturbing, because I can easily imagine pressing the doorbell button while wet and it is raining and I am standing on wet concrete wearing wet shoes. Even a 120 volt shock under those conditions is quite nasty, 220 volts would be many times worse..
 

panic mode

Joined Oct 10, 2011
2,672
i am sure there are rules to be followed. don't see why would that be any different than outlets or light switches that are outdoors or in wet locations.
 

panic mode

Joined Oct 10, 2011
2,672
using same logic, what is the reason to have GFCI outlets? should not GFCI be a separate device and in safer place like distribution panel? what if pipe burst and wall is wet?
if this was GFCI outlet, then outlet itself may be off thanks to built in GFCI but touching that wet wall near it would still be a hazard.
1689126100774.png
 

DickCappels

Joined Aug 21, 2008
10,123
Mine is 240 VAC - no point in complaining about it, that's the way it is in some parts of the world.

The electrician hooked up the doorbell (the original underground wiring only lasted a year or two) but ran "Romex-looking" cable along the steel fencing around the property. Since then it has been put into a conduit.

Several years ago I showed up at a temple here in North-East Thailand to run some wiring where new lights were being installed. When I arrived I was cautioned that some people had touched the chain link fence that made the walls of a building in the temple grounds and then fell dead from electrocution. That can happen is you just weave zip cord through your chain-link fence without proper insulation.
 

MisterBill2

Joined Jan 23, 2018
17,827
Mine is 240 VAC - no point in complaining about it, that's the way it is in some parts of the world.

The electrician hooked up the doorbell (the original underground wiring only lasted a year or two) but ran "Romex-looking" cable along the steel fencing around the property. Since then it has been put into a conduit.

Several years ago I showed up at a temple here in North-East Thailand to run some wiring where new lights were being installed. When I arrived I was cautioned that some people had touched the chain link fence that made the walls of a building in the temple grounds and then fell dead from electrocution. That can happen is you just weave zip cord through your chain-link fence without proper insulation.
I have done remote technical consulting work for a missionary some place in rural Thailand. And I am aware that the electrical codes are not quite so picky as here in the USA. But a chain link at mains potential must have been a serious electrical power drain even when it was not electrocuting people. I wonder what sort of excess current protection that fence connection had. And how can a chain link fence on steel posts have such a high potential. Ot maybe it had wooden posts supporting the fence.

The photo of water squirting from the outlet is impressive. I did participate in the installation of new outlet circuits in a building that did have water coming out of the outlet boxes, in New Orleans, back in 1967. The feed conduits ran in the cement floor two levels below the surface, and when it rusted through water entered and flowed up to the outlet boxes. Poor architectural design, it seems. That was in the LSU Medical School building.
 

panic mode

Joined Oct 10, 2011
2,672
The suggestion in post #2 would place buttons into low voltage circuit. Also this way there is no feedback loop or chance for circuit to latch up.
 
Last edited:

panic mode

Joined Oct 10, 2011
2,672
sorry, fixed the post. not sure how it got messed up like that.
by placing old button in parallel with button of the new bell, both are operating from low voltage DC circuit. i think this part should be clear.

the second part is about way two doorbell circuits interact with each other. it may not be immediately obvious but naive way is to make both trigger each other. that may sound like a good idea but it would create a feedback that would make both of them latch up when either button is pressed. then both doorbells would continue to ring indefinitely even after finger is no longer pressing the button. also next press on either button would change nothing.

and that is why proposed solution is the way it is. the only 'tricky' part is how to sense voltage across buttons. one may be tempted to simply use an optocoupler input side and a series resistor but this may not work if there is not enough current. a much better way is to use more sensitive circuit (logic gate etc.)
 

MisterBill2

Joined Jan 23, 2018
17,827
Use a comparator circuit with an opto-isolated output to monitor the electronic doorbell button, With a relay contact to activate the other doorbell circuit. The non-electronic doorbell button can operate a two pole relay to activate both circuits
 

Thread Starter

Anomajaya

Joined Jul 11, 2023
59
sorry, fixed the post. not sure how it got messed up like that.
by placing old button in parallel with button of the new bell, both are operating from low voltage DC circuit. i think this part should be clear.

the second part is about way two doorbell circuits interact with each other. it may not be immediately obvious but naive way is to make both trigger each other. that may sound like a good idea but it would create a feedback that would make both of them latch up when either button is pressed. then both doorbells would continue to ring indefinitely even after finger is no longer pressing the button. also next press on either button would change nothing.

and that is why proposed solution is the way it is. the only 'tricky' part is how to sense voltage across buttons. one may be tempted to simply use an optocoupler input side and a series resistor but this may not work if there is not enough current. a much better way is to use more sensitive circuit (logic gate etc.)
Thank you. I think opto-coupler won't work as the current is very low as you guessed.
Could you please send me a circuit diagram or a modular pcb of a more sensitive circuit that I can use in this scenario? As I mentioned earlier, my background is totally different from electronics, though I love to learn it.

Thank you once again.
 

Thread Starter

Anomajaya

Joined Jul 11, 2023
59
Use a comparator circuit with an opto-isolated output to monitor the electronic doorbell button, With a relay contact to activate the other doorbell circuit. The non-electronic doorbell button can operate a two pole relay to activate both circuits
Thank you so much. If you don't mind could you please send me a circuit diagram of a comparator circuit with an opto-isolated output that I can use? If I can purchase such a circuit as a module, that is also good for me as I'm not an expert on electronics.

Kind regards.
 

MisterBill2

Joined Jan 23, 2018
17,827
Quite a few comparator circuits have appeared on this forum, well drawn and easy to understand. My computer with the cad software is still out of commission after the lightning hit. But those comparator circuits are srtill aroind. Hopefully others can locate them and show the link.
 

BobTPH

Joined Jun 5, 2013
8,665
Maybe I am missing something, but this seems trivial to me.

Two buttons, in parallel, activate a single DPST or DPDT relay (from a low voltage source.) The NO contacts of the two poles are wired in place of the two original buttons.
 
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