Inside a door entry phone
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- Опубликовано: 9 авг 2022
- This brand of door entry system is probably the most popular in the UK. It's very simple, but is often installed badly by security companies, so it's useful to understand how it works to fix the legacy problems they create.
I'll cover the main door voice unit and button panel in a separate video. In summary, it's basically a simple power supply and a dual amplifier to amplify the local microphone to the common phone speaker buss and also to amplify the incoming common microphone buss for the local speaker.
This comes across as a well evolved legacy design that is refreshingly simple, but with lots of clever features. The use of a microcontroller to create the ring-tone was a surprise, but a nice one. The PIC microcontroller literally has just three connections. 0V, 5V and audio signal out.
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Got to be honest, when I saw the thumbnail I thought "Oh dear, Clive is getting bored in the crew accommodation and started dismantling stuff to see how it works".
At least they've got past putting holes in the ceiling. 🙄
That’s precisely what I thought as well.
This comment made me think of Alan Partridge disassembling his Corby trouser press.
Sending the indoor alert signal down the microphone line to the outdoor speaker, while disconnecting the indoor microphone, is quite clever.
Hi Clive, thanks that is really informative. I work for Bell System and that's pretty much on the money. I would love to show this on our RUclips channel ( very much in its infancy) and just asking your permission as an act of courtesy.👍
Yes, that's fine.
Thanks for dropping by Richard.
The "R" and "T" are (most likely) from the 1/4-inch phone plugs that were pretty ubiquitous in the telephone industry during the last century. "T" for tip, "R" for ring, and "S" for sleeve (usually the ground).
I thought it might be Rx and Tx!
I think T and R are for Transmit and Receive. The wiring is nothing like a regular phone and the T and R on this phone are not a balanced pair.
@@brianleeper5737 Then why is the "T" line hooked up to the _speaker?_
@@HiddenWindshield Look at it from the point of view of the control unit this phone is connected to. On THAT, T would be transmit to the phone, and R would be receive from the phone. Then consider that they had to keep the names / designations for the wires consistent from one end to the other OR confuse installers by telling them to connect T to R and vice-versa.
@@brianleeper5737 Look, you might be right. I wasn't there when they decided what letters to apply to which lines, and I don't have the manual in front of me, so I can't say for sure. But I do know that this would be the very first time I've _ever_ seen the transmit/TX/out/etc. line used as an input. Terminals are always labeled from the perspective of the device it's printed on (well, until now, if you're correct), and using Tip/Ring/Sleeve terminology would satisfy the "like connects to like" requirement without confusing the people who know what the letters mean.
I did actually try the "trick" of pushing the hook switch while holding the handset close to my ear all the while someone was ringing the flat where I was staying and I can confirm it was indeed deafeningly loud.
Also I discovered that nothing keeps you from tapping into the conversation when someone outside is ringing a neighbour, also you can even open the door before the neighbour.
Unlike modern, digital door entry phones (Or I should say _intercoms_ as that's how we call door phones here in France, well the french equivalent "Interphone", anyways) where you obviously can't tap into someones else conversation but you also can't open the door if no one has rung your flat up, and there's even a timeout when the communication is established, you can't keep chatting with your guest indefinitely.
Now from the outside point, most digital door entry systems don't allow you to call more than one flat at once and that can prove to be quite annoying for people like lift engineers when you call someone, they don't pick up and you have to wait before being able to call another flat.
I can confirm that others can listen into your conversation, I have a door phone like this in my apartment and there have been times when someone's called my apartment and I think another apartment, because my neighbours have picked up their phone and I hear them talking and I'm sure they hear me talking also. I daren't try holding the phone receiver near my ear while holding down the hook button while someone's ringing my apartment, I really dislike sudden loud noises, especially high pitched ringing noises in my ears, and my door phone has quite a high pitched ringing sound, much like the noise Clive is mimicking in this video.
Why would that even matter, every random guy on the street or through a window can hear what's being said through the door station loudspeaker. I don't think people would have to make their incriminating calls through an intercom phone.
Also, not being able to open the door seems like a bad idea if the doorbell button is defective.
I prefer a simple analog device over a digital one with the same functionality but which also bothers me with non-features 'for my own good, thanks.
@@westelaudio943 When you say "Not being able to open the door seems like a bad idea..." you're talking about digital intercoms, right ?
If so, I think first they're quite reliable, but also if the door doesn't open, the tenant will simply go down and greet his guest at the entrance door.
In fact I've seen blocks of flats where the first gate has an intercom, so the tenant can open to a guest, but then the guest has to walk on the open car park/courtyard to one of the buildings, and here there is another, locked door.
Tenants can open those doors (One for each building) with their RFID keyfob, however they must get out of their flats to open the door from inside whenever there's a guest as there's no intercom and the unlock button in the flat only opens the outer gate.
(Many years ago there was a code pad but they decided to replace it with a keyfob reader, obviously for "security" purposes).
@@westelaudio943 In the apartments I live in, the entrance to the apartments is a room and that's where the door station is, so you can't hear it from outside, you can't hear what's being said through an open window from nearby apartments, and you can't hear it if you're just walking past the apartments. I've got to be in the entrance area itself in order to hear it. But if you pick up your door phone in your apartment and others are using the system, yes you can hear them.
That was a security issue with these in the 1980s. Anyone could listen to the conversation, anyone could open the door.
The mic was always hot, you could listen to conversations in the lobby.
Still the same
I think this is kind of the old system our flat used. You could open the front door regardless if someone rang. So you could open the door even when the buzzed neighbor did not want to let the person in.
Another benefit was you could talk to anyone who took the phone off the hook. I used it in December to play Christmas music through the system (inductively so when they checked who played this music no sound was heard at my door.
All this was considered a privacy problem, so about 20 years ago we got a new system. Only, and only that phone is connected to answer the front door and open it is the one whose doorbel got puched. All others are muted and disconnected. I dunno how this is wired, the old 5 conductors-wire between apartments was reused.
This new system has a nasty flaw I encountered a few times.
When parcel delivery lad or lass has parcels for two flats he or she rings at apartment 42. 42 phone rings and the occupant strolls to the door. In the meantime, apartment 50 gets also a ring. 50 phone rings but the occupant's not at home. Phone 42 gets disconnected. Occupant 42 answers the door and takes a few seconds to realise there was no connection. Then starts to fly down 32 steps to catch the parcel. More than often to find the delivery person driving off leaving only a "Sorry, you were not at home" card with the notice the parcel can be collected the next day at some random bookstore. (We have no more postoffices, so parcels are left at [mostly] book and drug stores)
Interesting, so you are saying if you press 42 then press 50 the unit only tries to connect to 50? That doesn't really sound like a flaw, just means you can only call one unit at a time.
Maybe put a sticker note "delivery person, please only call one unit at a time".
The Postman seems to have a code / fob to gain access, but Royal Mail Parcels always leave a notice, which is also a ticket to collect the parcel, at the outside of the main downstairs door, for anybody to pinch (no letterboxes)
Suggestion for things to tear down: A cheap POTS analog phone. Would be interesting to see the circuitry used in one of them these days. A toner/probe aka fox/hound, the device used to generate a tone which is applied to a cable and the handheld device which is used to pick it up.
The original system these are based off used carbon microphone units indoors and outdoors, with a 9V supply obtained off the power transformer using a diode and capacitor, that then was used to provide a common 9-12VDC to the outdoor microphone and speaker, with the R and T wires then having the carbon granule microphone for the outside speaker, and the outside carbon mic driving the internal 32R speaker. The upgrades for this emulate the carbon microphone with either an electret capsule and a transistor or two for amplification, and for the speaker module outside the same, to use cheaper 8R or 16R speakers in the handset.
I have made carbon mic replacement units for them, ripping the dead carbon mic apart, and putting in an electret capsule, a PNP transistor and a 3k9 resistor between emitter and base to provide roughly the correct bias voltage, around 3V, across the mic capsule. Was a lot easier than buying those capsules, as they were failing rather rapidly due to age, and I could simply grab salvaged electret capsules out of old phones, a PNP transistor out of same, and select a resistor to bias it correctly. Fitted into the old carbon mic case, using the same connectors, as a drop in replacement. Much cheaper as well, which was a big consideration, and a lot better volume out of the speaker at the bottom as well.
3:30 was the most accurate recreation of a door entry phone ring I'd ever heard... until 5:30. (At 8:43 I SHOULD have learnt that I should wait until the end of the video before commenting; at 10:18 I learned that I hadn't learnt that.)
My last flat had a handset almost identical to that one. My flatmate had the cunning idea of installing a RFID tag opening system where a reader that was hanging out our window would 'press' the intercom button in the flat to open the front door. We then had a servo to unlock the flat door a few seconds later.
The hook switch in some of the earlier versions caused a lot of reliability problems, the contacts were a pair of long flexible brass springs that contacted bent wires, the contact surfaces would become tarnished and intermittent. The newer versions with enclosed switches are much better.
Probably the problem with ours...on an old Peabody block south east London (lalala)
Those brass spring switches were bent so that the contacts would wipe slightly, keeping them oxide free.
I have one of those
My door phone was made at some point in the mid 90s and lately when I answer it, I hear quite a bit of crackling noise through the earpiece. I rarely use the door phone so I'm wondering if the contacts in my door phone are a bit dirty or oxidised.
@@Lachlant1984 A likely cause
Here in Canada, these door phones have mostly been replaced by a system that rings your home phone. It requires each tenant to register their phone number (landline or mobile) with building management. Unlocking the door is accomplished by pressing a number (usually 9) while the call is live. Much more secure than the old door phone, but you can't participate without a phone.
A bit intrusive
That is a really weird idea. Lots of people have their phone on silent. Someone could be ringing me for half an hour and i would be none the wiser.
My late grandfather's place had something like that. I wonder what would happen if the person outside played a prerecorded tone of the number nine (or whatever the unlock code is). If that's enough to unlock the door it's pretty terrible from a security standpoint.
Same in newer blocks of flats in France.
There are also mobile apps for the intercoms by the way.
Anyways it really sucks because you need to have a phone (Most likely mobile) since they don't put handsets in flats anymore.
Aside from being a bit intrusive, what annoys me about the home/cell phone method is that you can't buzz people in without them calling you. I've had times when someone called my phone directly, and I had to tell them to hang up and redial over the intercom. I wish I had a physical button to just buzz people in regardless.
And I live alone so it's not an issue, but what about cases where two people live together? Lots of people don't have a home phone and just use cell these days, and being required to pick just one person to have entry control would suck.
Then there's the administrative issue of needing to register new numbers every time a new tenant moves in instead of it being constant per-unit, which was overlooked for me for *months* after I moved in.
And to top it all off, they still need a speaker in every unit anyway, for announcements and fire alarms.
8:50 "If you pressed them all, you'd get all the phones at once." And this would be an electronic version of the game that in my youth was called in Fife "chappie-knockie".
Knock down ginger where I'm from 🤣
When I was about 5 years old I did press all the buttons on an entry phone system (this would have been in 1983 or so) And a bunch of phones rang and a bunch of people picked them up, and I heard them all talking through the speaker at the gate.
@@brianleeper5737 Yes, I did that. Most amusing at that age, although I was a bit older!
The door entry intercom at the flat where I live is made by Tynetec. It seems to work a bit different to the one that Clive has described here. One problem it has is that if you answer between the rings and immediately put the handset to your ear, the chances are that you will get another extremely load and painful ring in your ear.
I'd bet someone at Bell got a raise for getting the handset speaker to produce the ring tone but it's a nasty choice for the curious who pick up phones and press buttons.
Magneto telephone circuits are the worst for getting a loud ringing sound in the earpiece. As the only thing in control of the ringing voltage is the calling person operating the phone at their end…
R and T stand for ring and tip, which are the two wires in a standard (at least in the US) phone line. They carry a current loop which is the sum of both signals, and traditionally there are specialized signal transformers at each end to split the signals apart. On a normal phone line, standby has 48VDC across the lines, ring superimposes a 90(?)V square wave on the pair, and in use the voltage drops to about 5-6V if I recall correctly.
As a trivia point, the names refer to the contacts on a phone plug as used on an old fashioned switchboard.
Interesting coincidence, I just had to analyze a 30+ year old system by Amplyvox out of Italy that was damaged by water from a massive water line rupture in a unit above where this controller was mounted. In theory it is the older version of the system you presented here.
This old unit uses two discrete channels running with TBA820M ic's with audio levels adjusted by two 10KΩ pots. One channel amplifies the mic audio from the main door unit while the other amp handles the mic audio from the apartment units. Very simple. If I decide to repair and keep this as a rebuilt spare I’ll shotgun both amps, pots, and all of the electrolytics as well as the terminal blocks that have rusted. Less than 10€ in parts and a half hour labor. Thanks for the informative video Clive! Thanks for the insight from several of the viewers comments as to how to replace the carbon elements with condenser units. Cheers All!
Nice to see them keep it simple even over time
Another great video Clive! and a subject I specialise in, I’ve done a lot of work on intercoms over the years, if you can name an intercom manufacturer I’ve probably worked on it.
The older legacy type that you mention all use the 3+1 or 4+1 wiring method, meaning a common 0v rail, a speech line from the door station and a speech line towards the door station, lock release is also a single wire return. I’ve made different manufacturers handsets work on other manufacturers door panels in the past just by knowing this. Intercoms over the years have evolved heavily with newest being IP based, some use the wiring method above but have extra lines so more than one door station can call a phone, these have ‘busy’ lines to stop other door panels being used when a conversation is in operation, others use a ‘2-wire’ bus similar to DCC in models train sets, with (commonly) 48v carrier and each handset being addressed.
I've never taken one of these apart but it reminds me so much of the first thing I ever took apart! I must have been about 6 years old. I had a play "walkie talkie" and because this was the 80s, it was just two cheap handsets and a 25 foot-ish cord between them. I remember grafting the speakers to all kinds of things and that was my first official "roll of 2 conductor wire" that I used on so many other projects later on.
I haven't thought about that in many years!
Another great video about stuff I didn't know about. In US I've only had the box in the wall jobs, push to talk/listen and another to unlock, however the switches were not as robust as this, and I had to walk down 2 floors to open the door since mine was broke 😁
you would be surprised how much fun one of these devices are for someone not used to using them!! my mother was forever pressing the ring button on the door to speak to my Aunty, so all she could really hear was the ringer all the time my mother spoken, until I confirmed with my Aunty that she could hear me without me pressing the button, I dunno how many years that had been going on for, as I was about 8-10 back in the mid 80's, and had always known my Aunt living in the block of flats until old age got too much.
from what I remember of the old units the handsets didn't actually disconnect from the door when the reciever was put down, as when sitting in my aunts flat you could quite often hear others using the intercom even though the handset was put in it's holder properly, so might be one bug that they fixed in the last 30-40 years.
Nice explanation of how this phone works. Very helpful for me since I have this phone in my flat. Hacking it so it triggers a remote doorbell was my 2nd electronics project.
Cheers Clive.
nice always wanted to see what's inside those devices! TY!
Very entertaining and interesting thanks Clive
Fascinating.
The building I live in, in Toronto, has a Mircom panel, with a dial pad.
You dial a 4 digit number, and that connects to the copper wire POTS system.
Every unit _must_ have a landline, for them to have intercom.
I've worked on various types of these over the years. Quite often modified or grotty wiring.
Ha I actually had one of these apart recently to add a Wi-Fi relay to open the door via Alexa or an NFC tag and my phone, still working out how to self power the relay module so currently I’m using a Poundland power bank thanks to you for the inspiration. At some point I’d like to build something that intercepts all the signals and allows me to operate it from anywhere like a ring doorbell
Very old school. The System in our house was installed ~2000 and it has a completely digital bus. 2 Wires (+Power) that is shared between all phones. It is also possible to call from upstairs to downstairs and vise versa. It's a Siemens system, the main unit is completely reprogrammable, it contains an 8051 MCU I think
"We haven one of these systems here. It wasn't installed very well." And that's why this one is on your bench with minimal damage. 🤣
I installed hundreds of these things during the 80's and they were quite unreliable the hardest part of installing these was drilling through the hardened concreate of each floor in a block of flats but we always used either a 6 or 8 core alarm cable even though they only needed 4 cores, nothing worse than trying to run a new cable through metal conduit if a cable broke down.
The thermostat (programmable, touch-screen heating and cooling) for my heat pump connects to the main unit with only 2 wires. Power and signals are sent over the same pair. One would think that building call systems could be constructed using only a single pair of wires for all connected units. Maybe they exist; I don't know.
I didn't know that was the reason!
@@tubastuff There are systems that use POTS (regular phones) and a single twisted pair. In these, the signal to unlock the door is sent by pushing one or two buttons on the phone's DTMF keypard.
@@tubastuff they do exist, as a bus system sending bus data as well as fm modulated audio&video over a twisted pair
When I also in college, I put a relay in parallel with my ringer (switched to disable it if I wanted), so when I came home with arms full of groceries, I could just press my room button downstairs and the relay would switch the main door lock open. Bad for building security, but they would have to know what random number to press downstairs.
Was extremely helpful thank you
Part of the reason for this video was to help people fix their own units so they didn't have to rely on building management companies and their contractors.
Used to install and repair loads of that bell systems gear back in the day on the housing association jobs.
Just ring all the bells and some one will open the door for you!
It was a very secure system.
There are many standards here in Poland, some of them use even 8 wires but there are also digital systems with only 2 wires to each apartment.
When I lived in a flat I set up a remote key-fob controlled switch wired across the door release on the intercom, so I could press the key-fob button (in my pocket) and buzz the front door open without having to get my keys out. Neighbours were mystified how I was doing this. EDIT: Just saw another comment saying they did the same thing! I did the above hack in around 1998, using a Velleman kit from Maplin. Shortly after vacating that flat in 2000, I noticed they installed a new intercom system.
I'd love to know how you did this as I share a front door key with my flat mate and regularly get locked out while they're out. (special key that we can't get cut)
"Traditional British Design" - that's when I expect a warning sign "Positive Earth" in the item I'm working with.
today I replaced the entrance panel with buttons and voice module on one of the most popular old Danish 4plus1 analog systems, so funny to come home and see how the UK products are designed.
Whenever clive is away from home like this I always just think he's pulling stuff from the local environment to take apart and reverse engineer like this, like he's just stolen the door entry phone from the accommodation to take apart and look through lmao
This video brought back a nightmare. Just over 10 years ago , my boss ask me to go and finish a door entry system on a factory conversion in to 60 flats, what he neglected to tell , it was a system install by another company who abandoned the job. Each flat had to have two phone , one in the hallway and one in the kitchen. There was 5 doors that entered the building they had to a 61 button panel , plus 5 electric locks , to cut a long story short I just rip the system that was there , the amount of cable trays and cable seemed to on for miles, it took 4 month ito sort out , by luck only 4 flat were occupied . I was only supposed to be on the job for 4 weeks , I was there for two years sorting out the rest of electric that were thrown in , just imagine all amoured cable , internet , CCTV, cable TV , door entry, satellite and telephone cable all thrown together with no separation between the different systems, a complete nightmare
60 flats but a 61 button panel ?
What was the last button for ?
@@psirvent8 Usually a trades button in series with a timeclock to allow postman etc to get in during the day
@@psirvent8 - Lucky dip, buzzes a random flat
@@rossBurglar But anyone can enter during the day ?
@@psirvent8 Often on doorststions with integrated keypads it allows a time limited trade code but yes sometimes it just releases the door. Access control keeps honest people out 🤷
I always assumed that the T meant Transmit and the R was receive, with the 0 being the common . In the 80's we used to install the old "Entryphone" gear, with "Eagle" handsets (which were marked TROZ1 with the Z being a phonetic rendition of the noise the AC lock made when you pressed the button to open the door, and 1 the switchwire that operated the buzzer in your flat) . We used the non-standard handsets because the Entryphone ones were diabolical and looked like the design had remained unchanged since the 1930's. The version with the video camera linked in was terrific, in that it's super-wide angle lens made even the most angelic looking caller appear like an axe-murderer.
It blew my mind when somebody finally pointed out to me that "electret" is to static electricity, as "magnet" is to magnetism: a permanently charged thing.
Your explanations should be shown to kids in schools. No exaggeration. You have explained it on the simplest possible level, so even person with no electrical knowledge can understand how this works.
Awesome Video big clive
Interesting, our home-brew systems (Tesla Stropkov, Slovakia) manages roughly the same but with only two wires coming up to each phone. each phone has a number programmed (in the case of ours, we have the fancier "reprogrammable" ones and you can even make calls from flat to flat if you know what number has the other phone assigned) which probably makes it possible. also not sure if this system does it, but ours disconnects ou after 30 or so seconds so you do not hog the line (or in case someone just leaves the phone off the base), has 4 ringtone intesnity settings (off/low/mid/high) and can have external button hooked up as doorbell and has different ringtone from the one downstairs (you just hook up any button so really easy to do) and can have auxiliary speaker hooked up so if you phone is far from the living room (99% of the time it is at the door to the flat) you can run the speaker elsewhere. also you can call from the top down if you want and spook anyone waiting at the door (not that I have ever done that)
At least here in the states, the red and green wires were called "Tip" and Ring". The terms date back to the 1/4 inch phone plugs (like headphones have) used by the telephone operator.
Early on, phones ran off a pair of big old 1.5 volt batteries (which later became popular for glow plug heating on RC controlled model aircraft). Battery power was fed to the carbon
microphone through a primary winding of a transformer The secondary of that transformer was what ran the lines going back to the phone office. Yet another winding fed your ear
piece...but kept the volume done so you wouldn't blow out your own ear drums since you are so local🙂...and feed back loops are pretty easy to establish. Also...it would seem that
the old military field phones operated in a very similar manner...although some distances had to be helped along via vacuum tube amplifiers in some locations. They were referred
to as east west west east amplifiers...as they only had "line" and "battery" terminals. You hook up power and the two talk lines and it would boost the signal both ways. Still scratching
my head over the schematics for those🙄. Oh...I see Buddy68 Is a Bell Tel guy...I was Western Electric back in the 70s and 80s. Hi, @Richard Alexander!😀 Oh...and electoret mikes
were pretty much designed to mimic carbon mikes in the early days.
Fun times. The micro switch was a huge upgrade in reliability
I install and service intercom systems to buildings for a living (amongst other things) and I have to say that nothing beats the simplicity of a 5-wire analogue system like the one shown here.
I live and work very close to the beach and salt is a constant problem with intercom systems. The old 5-wire analogue systems are so much easier to maintain and keep going.
Many buildings upgrade to newer digital 2-wire systems but I find they have way too many points of failure when exposed to the salty air and last a fraction of the time before failure, often pulling the whole system down in the process.
Take apart a newer Aiphone GT handset to see what I mean.. they are massively over complicated for what is essentially just an audio door entry system, with the same functionality as the one that Clive shows here.
I must admit the Bell system he shows here has some nice design features, most notably the tone being sent back down to the panel for an audible confirmation that your visitor pressing the button is actually doing something.
Many of the analogue systems I work on don't do this.. Urmet is the worst for it.. the old Aiphone analogue systems don't do it either. The big problem is when the visitors just push the button really hard and then end up breaking the buttons!
With the A/C buzzer ringer systems I have some low impedence buzzers I put in series with the common rail of the buttons and then mounted inside the panel so you get a audible notification at the panel of the button working. Because they are low enough impedance they really don't affect the loudness of the buzzers inside the handset which is great. With Aiphone I use a small low impedance speaker instead.
Nearly all analogue systems I work on here the call tone is generated inside the amplifier at the panel and not inside the handset. Often what happens as the traces start corroding inside the amplifier is the call tone sound starts leaking into the audio so there are many people who pick up their intercom handset and slightly hear the tone constantly in the background!
Anyway, very interesting to see this Bell system I don't see here in Australia. I wonder if they are even available here?
This was a long time ago but I recall a system at my grandmother's apartment building where you called from the lobby and the resident picked up their regular telephone to talk and the door release was one key on the phone handset (maybe #). Not such a good arrangement if you were busy talking on the phone when a visitor arrived.
Nice dive into these units! GreatScott did a mod on his appartment ringer phone thingy with mobile notification integration! ;)
Here's the video: ruclips.net/video/ZrkAWSemDC8/видео.html&ab_channel=GreatScott%21
I have a door entry phone like this in my apartment, I think it was installed when the place was built.
Spent a week repairing handsets and other parts of a more advanced Farfisa intercom system with 3 gates and about 7 door entries after a new psu was installed in reverse.
If there is one wire for every flat it seems that the harness going to the keypad could get rather sizable quickly. I would think for large number of flats some sort of serial communication protocol would win the day. But then you would have to have hardware to encode and decode the signal at every location.
Thanks
Thanks. Much appreciated.
Guessing R and T stand for ring and tip. That's the terminology used in the telephone industry, based on the old plugs (tip and ring) used on the cables that the operator would use to connect calls at the exchange. At idle, the tip was around ground potential and the ring was at -52V battery potential, with the nominal voltage at the phone being around -48V. When ringing a 20Hz AC signal of about 90V is applied across the line, in parallel to the battery potential. Because the ringer was basically an electromagnetic solenoid, the AC signal would literally push and pull the clapper between the bells.
I was moving my sofa today and broke my buzzer system. I took it off the wall and noticed it was just a telephone wire. So I've been researching how this works. I was going to pick up a new one. Instead I'm going to use my raspberry pi to replace the phone. I'll have that audio routed through to an app on my phone with a button to unlock the door over wifi. The phone I had was from 1991 and the circuit board is primitive. There's no micro controller for the sounds. Very interesting stuff.
When I moved in to my current flat I opened one of these and put a switch between the buzzer feed line to effectively turn it off, half an hour of trial and error as I couldn’t find a schematic for it anywhere.
"You can rewrite the ringer software"... - "EXTEEERMINATE!" :D
I install and maintain intercoms and security systems, i will agree that most systems are twisted and taped cables. its a right pain to diagnose faults when you have so many high resistance connections.
the R.O.T terminals on the bell systems are basically common, speech in and speech out.
the 801 handset you have uses the audio call signal which is amplified when the handset is on the hook.
they do another handset which has a simple ac coil that when energised makes a simple buzzing noise (if it were to receive a dc signal then no noise is made).
Most more up to date systems work on a 2 wire bus, this carries data for the voice signals and the door unlock signal, i believe the modern systems use dtmf, though ive never scoped the signals on the newer systems.
most of the time you will always hear an a.c humm on the intercoms, this is because either the system is using an a.c psu or the cables have been ran adjacent to the buildings mains circuit cables.
i hate fault finding on other peoples intercom installs, mostly electrician installs that use crappy telephone cables with hardly any copper on the cores, they always snap because they have more aluminium than decent quality cable.
maybe one day i will do you a video on an install that i have done.
i will re iterate, most security companies will install them correctly, its the electricians that havent got a clue about these things that will make a shit install of them.
In the USA the electric code does not allow the in-wall use of communications cable without solid copper conductors. Only exception is for coax cables. EDIT: This is not to say that stranded wiring isn't allowed nor to say that tinned copper conductors aren't allowed (they are).
@@brianleeper5737 unfortunately here in the UK every man and his dog can have a go, we have regulations for the install of fixed electrical installations but sadly not for the comms industry or security industry.
we do have certification bodies which i am a member of but theres nothing to say we have to use certain types of conductor. we do have to install low smoke and fume cables for fire resistance but thats about it.
would love our government to be a bit stricter on what we can and cannot use and who can and cannot work on something.
@@awolmadandy In the USA plenty of copper clad aluminum cable is sold and installed but it's an electrical code violation to use it. Doesn't stop some people but it could cause them some legal trouble.
At my place if someone ring me or anyone else everyone can her the ringing, just very faint.
We have a modern system, 10y old.
Any insight on what could cause that?
Interesting coincidence. Just finished analyzing a 30 year old Amplyvox control unit from Italy that was damaged by water. It uses the same basic wiring as the unit you displayed however it utilizes two discrete audio circuits based on the TBA820M audio amplifier IC. Each channel has its own 10K pot for volume control. A very simple system where on channel amplifies the microphones of each apartment unit while the second amp amplifies the microphone audio of the door unit up to the apartments. Instead of a micro controlling the ring tone you have a small electromechanical buzzer powered by AC from the transformer. This design appeared very easy to repair, considering the damage I will replace both audio amps, the pots and remove the carbon mic elements for the newer condenser elements. Speakers are 22Ω and sound a bit Tinny due to the fact that the apartment portion of the system is all in a flush mount wall phone set up. These can be replaced with newer handsets you have shown in the video.
Thanks for the information Clive! Cheers!
"Zed's dead, baby. Zed's dead."
Interesting, hadn't seen one like that before
T and R sounds like a normal telephone line with Tip and Ring.
Or TX / RX ?
@@barrieshepherd7694 not on an analogue system - Tip and Ring refers to the plugs they used to use on the telephone exchanges manyyyyy years ago...
Also, the speaker is connected to T, but that would be 'receive' or Rx...
@@stepheneyles2198 Pretty sure that Ring / Tip was to do with the polarity of the phantom power across the balanced pair that formed the telephone line, not TX/RX as such. It was necessary to get the connection the right way round as operators would tip test the line to see if it was engaged and if it was (indicated by reverse polarity) they were not supposed to plug the jack in.
The connection to the speaker is T but that may well refer to Transmit from the door unit. The R is connected to the microphone because it's sound to the door unit. i.e. the nomenclature is referenced to the door unit.
This 'reversal' is the norm in telephony e.g. the Exchange 'E' (signalling) wire became the Transmission systems 'M' (monitor) wire - and vice versa
@@stepheneyles2198 The ring and tip, as presented on the jack plug, primarily relate to the phantom power, across the balanced telephone pair. The operators would do a tip test (as teh plug touched screen when initially inserted) to see if the polarity, on the tip, was reversed indicating the line was in use and should not be plugged into.
As the telephone line is a balanced pair, carrying speech in both directions, Ring and Tip does not refer to TX or RX speech path direction as the pair carried speech in both directions.
In the door entry system the T is connected to the speaker as it's connected to the microphone TX from the door unit - telephone nomenclature usually uses the originator to define direction - as in telephone signalling where the E wire becomes the M wire and vice versa. (arguments about what E & M stand for abound 🤣 between exchange engineers and transmission engineers)
So the T wire transmits door audio to the 'subscriber' (the flat) and the R wire transmits the subscriber audio to the door unit receiver.
It's not on this one. Both the speaker and microphone signals are referenced to ground, on separate wires (T and R), and are not a balanced signal. Which means that this system could not be installed with regular twisted pair cable, some sort of shielded cable would probably be needed.
Sometimes (most of the time) bean counters kill the joy of circuit design. Sometimes the penny-pinching solution is quite ingenious and enjoyable to work out - as in this case. The efficiency and simplicity is quite artistic. And to think most of these end up in a skip somewhere eventually, probably still working.
We in Hungary have an older verison of this technology, with a code lock too. It's made by the polish Proel company. Interestingly that one only uses two wires for the flat's phones. It's a two wire bus going up to each flat. Wonder how that works. I guess it's somehow multiplexed, like a display. I think it recieves power, when somebody calls, it sends an 8 bit value on the bus, then the corresponding phone probably sends some other singmal back, same goes for the audio and the opening signal. I have installed some of them, to me it's fascinating that it acomplishes this with only two wires.
Edit: I think it's an 8 bit value since you can program 0-255 flats into it.
If it only has two wires I bet it's actually a more modern, like you said multiplexed system.
You can actually try the following tests if you want to know how modern your system is:
- Try unlocking the door without someone ringing up your flat. Is it possible ? If so that means it's an older and less secure system.
(Modern door entry phones don't allow you to unlock the door unless someone has rung you up).
- Again without anyone ringing your flat first, simply pick the handset and listen, can you hear the street noises or better someone talking to you from the street but without having rung you up ?
You can hear the person and/or speak to him ? Older system !
You can't unless your flat has been rung up ?
Modern !
Also on some modern intercoms (Or maybe all of them ?) there's a timeout delay once the communication is established, whereas on older and simpler ones like the one featured in this video you can talk with your guest for as long as you like.
@@psirvent8 It's from the 90's and 2000's, and no the doors can't be unlocked while not ringing, but you can hear the other people talking (on the older models in the same line of products) newer ones of the same thing don't do that. I talking about the Proel CD-1803/KDC-1803.
@@psirvent8 thank you, that was informative. I found out I have modern system but the odd thing we have is that if someone ring me or any neighbor everyone else can hear the ringing, just very faint.
Any idea what that might be and if fixable?
@@kimrosland It's probably a similar system which is in the video. Meaning that each flat has a separate wire, which the installers probably ignored, and wired it as if it were a bus line. Or they just didn't program the flat's phones correctly. Maybe all phones are programmed to the same number.
It would be fun to try reprogramming for custom ringtones. I know that is not the typical scope of the channel.
It would have been fun to have the ring play through a decent audio system the Addams Family doorbell followed by Lurch's voice, piped to the lobby: "You rang?"
The Japanese like the Westminster Chime on clocks for the hour. It would be a nice doorbell IMHO.
What the phone says? “Dülülülü dü dü dülü dülü”
Very impressed with the ring tone impersonations, have you had training? 😁
At work we use a simular system but the handsets only use 2 wires, each handset has 8 dip switches which you have to program in binary. its always puzzled me how this system works, my guess its the outside box sends a signal by PWM and the handset is doing most of the work, seems like a sinple way of doing it and replacing the hardsets is always fun, esspecially if you forget to program the dip switches or program it wrong :D
Inside a door entry phone: BigClive is a-DOOR-able 😉😉😉
I've fitted and repaired so many of these bell system intercoms. Very basic compared to themore modern systems
"Domofon" like it's called in Polish; it's straightforward unless it's a digital system. In that case two leads are commonly used (at least around here) carrying power, audio and control signals.
Using a microcontroller for ringing a bell is an enormous electrical & electronic engineering exaggeration :)
I guess you could use a 556 (dual 555 timer) if you'd want. But that's a 14 pin package.
Are you at the Edinburgh Festival again? Your video from there, last time, was really interesting.
That looks like the old pulsating 48 volt (DC) PBX systems that where installed in the United States AKA Tip/ Ring
The world of electronics gain having you is the British education system’s loss. You'd have made one heck of a great high school teacher.
We had a system like that in our 25 flat building - it was awful. People didn’t hang-up correctly after using it so you could hear what’s going on in other flats. Also people would just tape down the ‘Open’ button to let anyone in anytime - handy for dealers etc. We replaced it with a two-wire bus system using digital signaling and voice - much more secure and can’t overhear other flats or strap down the open button.
In the USA most newer systems seem to use a regular phone line with a controller module that is programmed with the phone number of each apartment/unit/flat. And when someone at the gate presses a button for a particular unit, it dials the programmed number for that unit. And when the person who answers wants to let them in, they dial a certain code on their phone and when the DTMF decoder in the controller detects the correct digits, it unlocks the gate. Similar systems are also used for gate/door control in secure facilities like data centers. I remember having to visit a data center on a regular basis and I would press the button at the door, I'd hear some ring back tones, security would answer, I would tell them who I am and what I'm doing there, and then I'd hear a couple of DTMF tones and the door would unlock. That one I think just used a ring-down device (phone line simulator), it wasn't connected to an actual PSTN/exchange phone line.
@@brianleeper5737 Great. Anyone with decent hearing and a touch tone generator can get in after initiating a call and people who lose phone service can't easily receive visitors.
@@tactileslut I think these units won't accept a DTMF tone from the gate side of the connection, and losing phone service isn't very common. These will even work with cell phones, if someone's cellphone number is programmed into the unit.
@@brianleeper5737: I think I've experienced intercoms like that here - you'll try dialing a flat number and end up getting someone's (default) mobile phone answering machine (or you'll get an answering machine, try calling the person on their phone number, and get the same answering machine). I guess on one hand you can leave a message that you tried visiting earlier, but I still don't like the idea of tying it to a mobile phone (while I did deliveries, I'd guess that those which I couldn't drop for were probably because someone's phone died or something)...
I guess the locking opening electromagnet was DC? The system I saw was obviously an AC magnet which sounded a loud buzzing. Or maybe it just had a buzzer.
For some reason, our apartment complex is wired in such a way that the only person able to disengage the lock or use the R / T lines is the last person that has been buzzed by the front door unit. So if someone rings more than one doorbell, only the last person rung can actually answer and open the door. This has lead to me missing a few packages already..
This is really ancient technology. They should have got into using SIP telephony decades ago. SIP is more reliable, probably cheaper, and can easily be expanded to include door cameras - all over a CAT-5 cable.
The least reliable intercom/door open system i've ever used, was a digital one. It never worked exactly right.
This is quite an old fashioned way of doing this.
The "newer" which have been around for a long time now, are just 2 wire. Often tan in Cat5. However will work on Cat3 (telephone cable).
The 2 wire will do colour video and audio. All addressable, handsets, multiple entry panels and 2 door.
Addressable is press call button then run to handset and press the lock button etc, not dip switch type addressable.
CAME. BPT, Videx etc.
The diode across the speaker might prevent feedback screech.
I have what looks like the exact same phone in my flat albeit yellowed with age. The "unlock" button has never worked in all my time living here.
Been threatening to have a go at integrating some of my home automation stuff with the door entry system in my flat but seems a little past my technical skill level atm. (system's a GDX 5 I think) I suspect it's a little more complicated than just shorting wires to make the lock open but not 100% sure, kinda afraid of testing that theroy and killing the door controller for the building.
reminds me of the first time I took the case off the phone in the kitchen, my mom was not pleased, it had big bells inside and a switch that would change it from ringing to a chime pattern, the switching system of the dial was always a mechanical marvel, to a 6 year old. how did it know which number you dialed? Thanks for that Nostalgia.
with all those tulululu's he could start recording ringtones for intercomms
We need to find a waterproof system, not just one that says it is. My front door faces out to the North Sea and gets battered by salt water and rain. Also if the other flats dont hang up correctly we can hear them taklking and the sound plays out to the people walking past. 👌🎵🎵 Neat video of much used system. 2x👍
Just rotate the apt.comp 180*
@@kimrosland that might help But the wind just rips over the cliff and right into my entery way somed ays we cant open the door .👍 Thankfully we have more than one way out
They should bring back the old hand crank dynamo PSU so we can all get a bit more exercise in our day.
I still have entry phone like that in my apartment and they aren't planning to replace them because they are getting the job done
may I suggest a topic here? How about you look at those "toner chips" they use on ink/laser toner cartridges to estimate the remaining toner level? I suspect they are just a memory card. It might be nice to be able to reset faulty ones like the one I have to take out and put back often because it is spotty (probably dirty contacts).
I'd like that.
The toner chips are asics (application specific intergrated circuit, for the noobies out there) they are not ONLY memory i think, i think also some digital control logic or even crazier a microcontroller maybe someone like electron update can do a decap cause he has done many decaps of chips its a great channel check it out
Hi Clive, Are you at the Tattoo this year? I was looking out for you, but didn't see you, but I didn't really get to see behind the scenes. I know in the past you did some behind the scenes filming, that was always very interesting, like the crew's own beer. etc. Keep up the good work. Thx Andy
Same as I have in my flat. Absolute shite and feedback is awful but I took the handset apart and filled it with offcuts of audio deadening foam. Reminds me of the 90s Eagle Electronics
Not at the tattoo Clive?
Actually, just noticed the backdrop is different. So you're working remotely. Hope you're having fun.
The large microphones that don't require amplification are carbon microphones.
Given the labelling of the wiring I was expecting a traditional telephone hybrid and a carbon mic. I suppose the speaker unit then contains the echo cancellation/sidetone circuitry.
The mic in the older unit did actually make me ponder if it was actually a carbon microphone.
You mean intercom, Clive!
If two units pick up the hand sets, can they talk to each other? ... Like, knock three times on the ceiling means pickup the hand set? ... You could 'telegraph' to any one in the complex 😀
Two people can pick up but they won't be able to hear each other well. They will only hear the other person through the microphone at the building entrance.
Dear Clive. Having enjoyed this excellent video on the entry phone, I could not understand what the 2K7 Ohm resistor (at the top) was for in the ringing\audio circuit. If the high sound was activated then as you say the current just goes straight through, but if on low, it would have gone through the 100 Ohm resistor. If the 2K7 was to assist with a mid point above for the 100 then surely one resistor matching the required value would be better and save costs. Have you any ideas or have I just misunderstood the workings? Many thanks to Clive or anyone else in advance.
8:30 Does that mean that you could tap in to that with an external sound source and randomly play sounds downstairs? That would open up so many prank possibilities...
I recorded your dololololo and put it in my micro-controller, yours sound a lot nicer, like a singing canary! 😝