I'm new & early 00's intercom system - Page 1
Forum section: electronics / beginners

author: DJVG
author_rank: Contributor
timestamp: February 12, 2016, 04:14:59 pm
content: Hi all,I just registered here after watching the EEVBlog video's for months. You're doing a great job Davereally enjoy watching the video's and I'm learning new stuff every day!Let's start with introducing myself, my nickname is DJVG, I'm from a small city near Amsterdam, the Netherlands. I work in IT, maintaining large scale Linux based server farms for a US based company.My electronics knowledge is really really beginners level, I thought this forum section would be beginners but my knowledge is far less than the questions here. I have played around with an Arduino board and some leds and I did some small things with a RPi and a I2C 16x2 LCD. I have some C knowledge and understand how to program a simple thing to show chars on the LCD using the RPi but I've got no idea how I2C exactly works.This all doesn't hold me back to learn more about it. I always have idea's on new things to create. The last thing I created is a power logger for my house kWh meter and create nice graphs. This works fine but really easy.Now back to the other part of my topic title: the intercom system.In 2013 I bought a house from the 70's, this house is equipped with an intercom system (called "Bode", which translates to "messenger" in English) from the beginning of this century. It has a lot of functionality like the standard intercom (voice + video + door unlock) things but also ordering groceries, an alarm system and access control. Unfortunately the contract for all those cool features has been discontinued so I can only use it to see who's in front of the door, speak to the person and open the door.Because I would love to create my own system for this (with phone notifications, storing pictures of people that are ringing the bell etc...) I reached out the company that build it in the past to understand how it works or get service manuals. Long story short: they're not going to give it to me, It's all proprietary and they don't want to help me. Perfect.The only thing they wanted to tell me is that the voice part works on a open 1+n system. I've searched on google for hours, nights, months. But I can't understand what a 1+n system is, I just don't understand how voice gets transferred over the cables.So where am I know? The intercom is analog as far as I can tell, they use a RJ45 connector to connect it to the system in my house, there's no TCP/IP traffic on the RJ45, they just used it because it was easy is my guess.I figured out the video system, which is a normal composite video as far as I can tell (I was able to watch the camera on my TV using the composite input). Also I figured out which cables I need to short to open the door downstairs and that's it. With the knowledge I've got I should be able to connect the video to an RPi and open the door using a relay (sorry if I'm saying something really stupid now) but I didn't figure out the main part of this whole system: the ringer and talking with each other. I did read somewhere that intercoms use a 45V AC input to trigger the ringer.The system in-house consists of 2 parts. The one in my electrical room (sorry, I forgot the right word) where my main AC is coming in (lets call it part A). And the part that I use to speak with people and see the camera (part B). Part A has a lot of in and outputs, it has a phone connection to call the system to order groceries etc... (which is not in use anymore), the output for my in house ringer and the two important parts: Main system input (RJ45 from the building) and Part B output RJ45 connector. It also has two batteries to keep the alarm system working when there's a power outage. I disconnected those because the alarm system is not working anymore and I don't like having batteries connected for no reason.It looks like Part B is running on an Intel 386 processor, but I'm quite unsure about how it all works together.To clear things up I created a lot of pictures:Part A:Part B:My question now is where do I start? Where should I get the knowledge on how to "hack" my way into this so called "protocol" to understand how it works an evnetually connect it to a RPi for further processing.I appreciate any help in this!Regards,DJVGP.S. Sorry for my English, it's a bit rough around the edges.

author: Audioguru
author_rank: Super Contributor
timestamp: February 13, 2016, 12:23:55 am
content: An intercom system has a microphone, amplifier and speaker at both ends. If you connect your microphone to the amplifier and speaker at the other end and connect the microphone at the other end to the amplifier and speaker at your end then you will get audio feedback howling if a microphone can hear its speaker because the sounds go around and around.Cheap intercom systems fix it by using "voice switching" so when you talk your speaker is disconnected and when the other end talks their speaker is disconnected. Then both ends cannot be heard at the same time and frequently voices are cutoff by noises at the other end.Expensive intercoms use a complicated "digital echo canceller circuit" that prevents feedback by making a model of the acoustics and cancelling it.

author: DJVG
author_rank: Contributor
timestamp: February 15, 2016, 01:46:45 pm
content: @Audioguru, thanks! I should be able to understand how a intercom system works, I keep thinking to complicated is my guess.Today I decided to completely remove part A from my mains cabinet and checkout all the components (mainly the intercom input from the building) and I found the following information:2 connections are going to a relay: V23105-A5003-A201. Spec sheet:http://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=108-98007&DocType=SS&DocLang=EN1 connection is going to another (same type) relay.1 connection is going to a Line Matching Transformer: SM-LP-5001. Spec sheet:http://www.mouser.com/ds/2/54/MLP5001-778036.pdfMy thoughts so far, the relays are used to switch when someone presses the doorbell at 12VDC? The Line Matching Transformer is used to do something with the audio, not exactly sure what though.After measuring I found also four voltages coming into my house, 12V, 9V and 6V and 66mV, all DC. I think the last one is for video. But I'm not sure what the others do.I've also got issues to identify those two blue bricks:I'm sure all of the above is caused by a lack of knowledge but I want to learn it!Edit:I hope to understand the ringer / voice part without the need to press the doorbell because I'm alone and I can't be in two places at the same time. That why I want to understand how it works and try to recreate it in a smaller version.

author: Cerebus
author_rank: Super Contributor
timestamp: February 15, 2016, 07:37:20 pm
content: Quote from: DJVG on February 12, 2016, 04:14:59 pmDon't worry, your written English is better than that of some supposed native English speakers around here!Quote from: DJVG on February 15, 2016, 01:46:45 pmThat bit's easy, it's two 4.7 microfarad capacitors, 250V rated, made by Epcos (I recognize the Logo).QuoteIt's probably what's called a 'hybrid' transformer - used in telephony to allow two wires to carry speech in two directions simultaneously. It's a bit much to explain here but search for "telephone hybrid" for a full explanation.A quick look at the boards you've photographed suggests to me that we're probably looking at mostly classic analogue telephony style electronics here - the Lucent parts suggest that - mixed with classic CCTV style electronics - the Phillips parts suggest that. And then that's all topped off with some digital control and management.Think you've probably got your hands full reverse engineering that lot - it'd certainly keep me busy for a few days. Good luck!Ian

author: C
author_rank: Super Contributor
timestamp: February 15, 2016, 09:30:38 pm
content: Reverse engineering might not be that hard.Look at what needs to change from the old analog phone system.Removing main DC source from audio wire pair. Most stations will need more power then can be easily supplied with audio on pair. A second pair for power makes sense.Keeping a Ring signal on a pair would allow stations to power off when not in use. Ring supplies power needed to power up. Again makes sense if feature is wanted.If the intercom also has music output then more wire pairs is easy way to get more audio sources.If you have an audio system and want to add Video do you drop all of old system or add video to old system and some stations.You also have the make one station a little more expensive to lower cost of all other stations.QuoteWhat you are calling a (RJ45 from the building) could be a RJ31X. Often used for alarm systems and other things. When plug is removed some terminals get shorted to other terminals. With plug out, normal phone service. The equipment connected via this plug has capability to drop and make a new call. So a phone left off hook will not prevent a alarm system making a call.

author: DJVG
author_rank: Contributor
timestamp: February 15, 2016, 09:52:02 pm
content: Quote from: Cerebus on February 15, 2016, 07:37:20 pmHi Ian, thanks, that's a big compliment!Quote from: Cerebus on February 15, 2016, 07:37:20 pmI don't exactly know why they are used on this board, but I think this has something to do with the batteries (It can switch to battery mode when the main power fails, this is used for the alarm and access control I assume, doesn't work anymore).Quote from: Cerebus on February 15, 2016, 07:37:20 pmI think the voice part is really easy (I think...). There's a lot more on this board than needed. I found a couple of DTMF decoders because it can call out to a main computer for your groceries, do some ACL work and alarm functions. All of the extra functions are disabled. Only ringing, talking and opening the door works. If I understand the "telephone hybrid" thing correctly, this could be what they mean with "1+n" protocol.Quote from: Cerebus on February 15, 2016, 07:37:20 pmI think this is a good thing haha. I really want to learn how this kind of stuff works. If I compare it with a conventional telephone system the ringer might work by sending a higher voltage (90VAC+) to trigger the ringer. When you pick-up the phone the sending party (local system in my case) will detect a change in current and switch to the "telephone hybrid" system so you can talk to each other.If I look at all of the above I really need to have someone that can keeps pressing the doorbell and I can measure a change in voltage on a cable. If I can measure a change that will most likely also be the voice line too. If I understand the phone system correctly I need to understand how to receive and send "voice" over that cable.Thanks for your input, I'm sure this will make things more clear for me!Quote from: C on February 15, 2016, 09:30:38 pmI'm currently changing system in my house only (create something myself). All the voltages are currently on the cable and I can't remove those because they're coming directly from the main system in this building.Quote from: C on February 15, 2016, 09:30:38 pmWoow, I thought directly about RJ45 (the connector is exactly the same as a RJ45 connector) because of my networking knowledge. But RJ31X looks really the same, I don't know if the RJ31X connector is a standard because the wiring in my connector has video included. Thanks for your information, going to drive into it!

author: Cerebus
author_rank: Super Contributor
timestamp: February 15, 2016, 10:58:36 pm
content: Quote from: DJVG on February 15, 2016, 09:52:02 pmMyguessis that they are DC blocking capacitors for a phone line, or phone line like section of intercom. The 250V rating fits with protection from the possible extremes like 90V rms ringing currents and the 4.7 uF is too low a value for any power related function especially when it's taken together with the high voltage rating.