Updating an Old Music & Sound Intercom System with Skybell HD (Part 1 of 2)


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Skybell is a video doorbell similar to Ring. These devices are intended to be hooked up to existing doorbell systems. Most traditional wired doorbells have a transformer that drops the high voltage/high amp of household current to lower voltage and amps compatible with your doorbell chime whether analog or electronic. The two wires coming out near the exterior doorbell button lead to the transformer – so for the Skybell you normally need only to detach the wires from your doorbell button and attach them to the Skybell. That way when you push the Skybell button it not only sends an alert to your smart phone but also rings your normal doorbell.
 
 

The Problem – Skybell is Not Compatible with Intercom Systems

 
 
 
Unfortunately our house was equipped with an old 1980’s style Music & Sound intercom system. I had previously equipped the system with a Google ChromeCast audio so I can wirelesssly cast audio from my smartphone to all the rooms in the house using the M&S speaker system. I removed the radio/intercom unit from the wall, tucked the Chromecast to the side of the internal unit, and cabled the wired out the back behind the sheetrock to the outlet below. The 3.5m audio connector plugged into the internal RCA “aux” plug. I also attached a Google Home Mini on the wall above it and a tablet nearby (see my previous post).
 

 
The M&S Intercom has wires leading from the central intercom unit to speakers in each individual room of the house. In addition, wires from the doorbell button run from the front door through the attic, across the house, and down into the wall, coming into the unit and attaching to the chime. See orange and red wires below:

One would think that one could attach the doorside ends of the orange and red wires (now connected to the doorbell button) to the Skybell. But that doesn’t work, as first they won’t power the Skybell, and second, the Skybell button won’t trigger the chime. Watch this video for an explanation as to why intercom type doorbell buttons do not work with Ring or Skybell (I would suggest that you may want to just read the comments and save some time). Skybell does sell a chime adapter but it doesn’t work for Nucom or Music & Sound type intercoms. In fact Skybell has an explicit statement on its site that the Skybell is not compatible with intercom systems.

DANGER: THIS POST IS FOR EXPLANATORY PURPOSES ONLY TO ILLUSTRATE ONE WAY A SKYBELL WAS INSTALLED. DO NOT ATTEMPT THIS WITHOUT CHECKING WITH A QUALIFIED ELECTRICIAN AND CHECKING WITH LOCAL BUILDING CODE. WIRES AND TRANSFORMER MUST BE OF SUFFICIENT CAPACITY; WRONGLY SIZED, CONFIGURED, OR WIRED SYSTEMS COULD CAUSE FIRE OR EXPLOSION. EACH INTERCOM SYSTEM AND TRANSFORMER IS DIFFERENT AND MOST LIKELY WILL BE DIFFERENT THEN MINE. IT IS VERY POSSIBLE YOUR TRANSFORMER MAY DESTROY YOUR SKYBELL!! ALWAYS TURN POWER OFF FROM THE SWITCHBOX BEFORE WORKING ON ANY POWERED SYSTEMS!ANY ATTEMPT TO FOLLOW THIS POST IS DONE AT YOUR OWN RISK.

 
 

Removing the Intercom from The Wall

 
 
After a lot of thought, I decided to do some exploring. I turned the power off, and removed the intercom unit from the wall.  The unit was fitted into a green metal cabinet fixed to the wall. In the right rear corner of the cabinet there was a corner that was encased with a small solid metal removable box to which an electrical plug was attached.

 

 

 


 
 

The Transformer

 
 
I removed the plug, removed the screws holding the sides of the transformer box in place, and revealed the transformer.

The transformer was stamped secondary power “20V 24VA”. This meant that it was 20 Volts AC (or 20VAC) with 24 Volt Amps. To get amps you divide 24VA/20VAC and get 1.2 amps. I’m not an electrician but this fit the power requirements of the Skybell which required 10-36 VAC (my transformer was 24VA so was within range) and 10VA – so max amp requirement was 10VA/10VAC or 1 AMP.

How to hook to the transformer across the house from the door ? I could have installed new wiring. But the wires connected to the chimes were of sufficient guage, and there would be no need for the old doorbell button or chimes any longer.
 
 

Rewiring the Doorbell Wires

With ALL POWER OFF, I unhooked the ends of the orange and yellow wires from the doorbell chimes, pulled the red wires out of the transformer plug (the end on the radio side of the transformer box), connected the one red from the transformer to the yellow wire, and the second red from the transformer to the orange wire, and inserted each wire set back into the plug holes that the red wires came from. Now we had sufficient power connected to the front door.

I then went outside, pulled the old outside intercom/door bell mechanism out of the wall, cut the orange and yellow wires off the doorbell button, and connected them to the Skybell. I did this only after verifying with a multimeter that the voltage and amps were correct.

 

The skybell works like a charm.

 

 

 

 
However there remains a problem – the inside door chimes no longer work, the Skybell is only being powered. While it can send notifications to our smartphones, it is not able to trigger the chimes. In Part 2, I will explain the software side of getting a doorbell to ring inside the house to my Google Home Minis and Chromecast Audio receivers using a Raspberry Pi, Google Notifier  and Skybell Sniffer.

To Be Continued in Part 2 …