Multi-Line Telephone Intercom
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- เผยแพร่เมื่อ 2 พ.ค. 2019
- Modern smart phones have become so ubiquitous these days that old analog phones are getting left in the dust. However, you may still have a few of these old phones hanging around your house collecting cobwebs or you may have seen some lingering on the shelves at your local thrift shop. Now’s your chance to put them to good use. In this video, Derek takes you back to a time when stretching a phone cord across the room was the norm by creating a 4-line telephone intercom system with basic ringing capability. The circuit surrounds a DTMF decoder IC which handles keypress detection, a simple AC inverter to handle the ringing and a current source which allows analog communication between multiple phones: bit.ly/2Leyf7C
- วิทยาศาสตร์และเทคโนโลยี
Finally, new content from one of my favorite youtubers, The Current Source! I'm so glad you are doing well!
Derek is my favorite host on this channel so far! Great work!
Holy crap, I haven't set up a system like this in.....decades...thanks for sharing! Loved it!
A known pair of 26AWG wire, one 9 to 12VDC battery and two test sets are more than enough to have two lineman/splicers to work together on phone lines. Thinking about this makes me missing that time... except when it was cold, hot, rainy, snowy, icy rain, windy in humid man holes or on spikes at the top of a pole for twelve hours. Keep up your excellent work!
Very professional, quality content. Thank you! I have collected some old phones in the hope, that I will use them in a project like this some time. At least now I know how to do it properly.
I made something simmilar for one of my first microcontroller projects. Your design is very nice, and I'm thinking if someone added a microcontroller to it, the "ring" line could also become a second line for 2 private conversations. With a few small changes I must add. Great project man very detailed!
Obviously if you want a second talk circuit, you'd need numerous more relays. It becomes an entirely different project. This project is basically "selective ringing."
Nice! I’ve scoured the internet looking for a commercial solution for something like this, and couldn’t find one. I’ve got a bunch of ancient phones, and will give this project a try!
Good luck with your project! If your phones are *really* ancient, with electro-mechanical ringers, this power supply may not provide adequate ringing voltage.
I'm liking very much! And to think, I spent a wad of money to buy a pabx to do this job. We connected my cabin and my dad's bungalow, and then added a few other phones around the farm, not so much that we needed them, but because we had all those spare outputs going, well, spare!
That pabx is a pretty well feature rich system, and it does its job admirably, but it's not as much fun as this setup!
Years ago, we had a very basic "upstairs/downstairs" (two telephones) and basic power supply so that we could call from ground to first, and vice versa, floors of the house, but it lacked the sophistication of this system. It could only ever be two phones, commoned on a single DC line, with a separate ringer circuit.
A Nice video/tutorial, thank you.
This video was so good. Thank you for the content. It's nice to have a project I could make and understand that wasn't hooking a Pi upto something..
Thanks for the video. It turns out it's kinda easier than I thought. I'm building a half scale M4A2 Sherman tank for a School project. And I was looking around to see how to make an intercom system and now I know how 👍🏼
Very cool and simple project. Thanks for the video.
I built my own relay-based PABX when I was in college ~1965. It was all rotary pulse dialing, no DTMF. In addition to phones around the house (my brother's room, dining room, darkroom, etc.), we strung phone lines through the trees to some neighbors houses so we could talk to our friends. Rather than a common "party line" only the called party could talk to the calling party. Also used a real 20Hz 90v ring generator, since the phones all had electro-mechanical ringers.
Thinking about your project, my personal feeling is that if anything needs improvement it's the ringing generator. Indeed, the high voltage requirement presents some design challenges. If I can come up with any relatively simple solution I'll send it along in case you ever want to make a "Mark II" version.
Oh yeah ... wasn't it a PITA to punch the holes in the steel chassis? Solve that problem and the rest of the project is cake!
Nice! How did you manage the part where only 2 ppl could speak to each other? Can't wrap my head around it.
@@BurkenProductions Thanks. I'm not sure I understand exactly what you're asking, but let me summarize how my system worked.
Each phone had its own series "line relay." Initially all the line relays received voltage from the supply. When one phone went off-hook, that removed voltage from all the other line relays; so other phones could not initiate any actions. Thus only one conversation was possible at any given time. (Given that we had only 7 or 8 extensions, and only 4 people were normally involved, it was unlikely that we'd have a need for simultaneous conversations.)
The "active" phone also controlled "B" and "C" relays, which in turn controlled the stepper switch. When the phone dialed some other number, the stepper selected the "called" phone. If the called phone was (presumably) on-hook, ringing voltage was sent (via stepper switch contacts). If/ when the called phone went off-hook, ringing voltage was disconnected and called phone was connected to calling phone. That allowed the conversation.
I honestly don't remember whether the two phones had a DC connection path, or whether there was a series "talk" capacitor connecting the called phone back to the calling phone. In the former case, the system would remain "tied up" until both parties hung up; in the latter case the system would be controlled by the calling party.
In retrospect some other features would have been nice ... maybe some sort of audio tone injected into the talk circuit if a *third* phone went off-hook and wanted to use the system. Then when the first two parties heard that tone, they could hang up, freeing the system for the third phone. Etc. But this was 1965, when there no such thing as consumer-level logic chips, and I was spending my allowance to buy surplus relays.
If that didn't answer all your questions, let me know and I'll try to recall more details.
Cheers!
Exactly what I was looking for. Very well explained. Thank you so much ❤️
Explaining tech, you're doing it right. I was thrilled.
Hey you are the guy from The Current Source. Nice to see you here
I am! Thanks, it's nice to be here.
Awesome video! Very well explained and interesting content. Looking forward to more videos.
Big thumbs up to this guy. He's really good.
I've always wanted to learn more about analog phones. Great video, too bad about the low amount views though.
You could use a binary to decimal decoder chip to extend the number of lines.
I have build similar ring generators using a astable 555 timer driving a push-pull amp with 2 power transistors and a large value cap in series with the out put, works great.
IMHO that's a much better solution than the one presented here. Better waveform, fewer HF harmonics so less problems with transformer impedance, etc. The challenge is finding a transformer that can pass 20 Hz with reasonable efficiency.
I have sort of enjoyed telephone systems, especially electromechanical exchanges. I think what you made is a very crude PABX
Nice to see you on this channel :D
best explaination on how telephone works ,ever !
This is not a bad explanation that gets you most of the way for an PBX. Add an arduino such that if a party line is in use, then other calls can't be made. There are some chips that is made for the matrix switching, such as 8 rows by 8cols or even 16 lines. This video and schematic has got me thinking!
There is a company that makes a module that will provide 90 volts at 20 Hz. Unfortunately I do not have the link saved on this computer and the other machine is in deep hibernation.
A multi number add on would be nice for this system, don’t have to worry about dialing binary. A simple 3 or 4 digit extension would suffice. No need to have fancy ring cadences either. The only thing a ring cadence would provide is a signal to a decoder within each phone on the system so it knows when it is called. Would eliminate "home run" extensions when a loop would suffice.
You gave me an idea of repurposing a box of old telephones. I just ended up just buying a pabx unit due to my lazyness but thanks for the idea! :D subscribed!
😆 loving the video editing
Thanks man for sharing your art
U r wonderfull... Thats content I was googling long time... thanks to share this.... well done
interesting topic and great explanations!
In my retired years, I now help out with the senior center's drama club. I am the sound guy. I use the PA system for all sound reinforcement and sound effects. One of my projects is to use old phones for certain skits. Ringing the phones would be great. So far, after reading up on the requirements for ringing the older phones needed a current of ~ 90 v. @ 20 HZ. So according to your video, that spec. can be obtained without too much bother. So, can I actually build a circuit for this. A little help would be much appreciated. Thanks Dale Mettee
Very simple approach. Congrats. I am surprised that you did not have to add a series choke inductor on one of the line wires. The 33 ohm resistor + LM317 have a rather low impedance compared to the audio signal. When I tried this back in the 80's, I had added the primary winding of a power transformer in series with the +9V DC supply, otherwise we would not hear anything. Thanks.
Yes, you need a coil in serial with the power, otherwise you will just kill the audio with the power supply, but here they use a resistor, will work but not that well as a coil.
Agreed 100%. Think about a TELCO central office subscriber line circuit. A big mother 48v battery (0 ohms AC impedance) in series with two relay coils which produce a *high* impedance to the audio.
Great project!
Cool video! I’ve actually been thinking about old phones lately and what to do with them
I've improved on the design a bit, adding the ability to address 8 individual phones and the ability to access a landline etc, I've added a microcontroller to the DTMF decoder and a 74HC138 to the ring relays. I have to revise the board a bit but if you want the design files etc let me know
Can you send that to me as I am very interested in this
I am also interested in this project
@@sam462m github.com/WRFleete/PABX-project has the code + schematics + gerbers, havnt tested with the RJ45 connectors on that schematic etc but I did have individual ports for each phone. Code may be a bit of a mess and I may comment on it a bit. The code has basic support for pulse dialing as well and the ability to connect to a POTS/PSTN phone line (and dialing to get the "outside line" and "hold" feature)
@@rossherbert1591 posted a link in another reply to the git repo
i have been looking, for a long time, this informarion. thank you very much
Useful article.. Regards from lines telecom 🇮🇳 india
Awesome idea and knowledge 👌
Nice simple system for a large house.
This is so wholesome.
so informative and clearly explain i thank God for I found this thanks a lot element 14
is there an off the shelf product that can do this? I would be very interested. Perhaps decommissioned business phone systems?
I miss those old golden times.
Very cool project... I am going to have to try this!
By the way... where did you get you facehugger shirt?
16:40 lol, this is a great little vid, thanks 🙏🏻
I want to know, Matrix Visionpro308 maximum distance from epabx to normal beetal c11 phone distance ?
Hey, It's pretty cool one ! Can you please make a project of circuit acting as bridge to connect GSM SIM module (eg SIM800L) with normal phone instrument (Benatone Concept 711) to dial phone and receive calls coming to sim number ?
Awesome!
Hi , I tried this project . But I find that the relay keeps chatterring and the bell keeps ringing in the phone. could you help me to rectify this ?
Could you utilize the power from the phone line itself and could you make an intercom even though the land line is still used as an outside line? Very interesting. Interesting thing is our home was setup initially to have 4 different land lines and all the lines still have power.
It's not clear to me exactly what you want to do. However, the TELCO phone line provides a maximum of about 50-75 mA, not nearly enough power to run the ring generator and other electronics in this system.
Dip package is easier for the DTMF decoder if you can still find one
I might make some improvements to this and design a proper PCB, I might use discrete logic (or maybe an arduino) to decode the DTMF decode output to individual signals for the phones so at least 9 or so phones can be used and maybe use 0 to switch into to the landline etc if used. I would have to treat the phoneline as another phone and design the input of the landline jack to act as if it was a regular phone, so it will likely need to be isolated and need to detect ring signals broadcast to all phones and take the line off hook when any of the other phones go off hook
You don't need an Arduino. Just use a BCD-to-decimal decoder, e.g. 7445, to drive the relays. Interface to landline using a relay and 600:600 ohm audio transformer, and you'll need some logic to keep that landline circuit latched on until the calling local phone goes on hook.
Nice, but how do we make it capable of loop-disconnect dialling? Oh, and can we do it entirely with relays..,
:p
Thanks for the explanation! I may have just missed it, but can you please explain how the system recognises when the phone receiving the call has picked up? I dont understand it, as I can't see any way for the circuit to determine if phones are on or off the hook.
The system doesn't recognize when the phone receiving the call has picked up, but only rings for as long as the caller is pressing his keypad button, so a quick press should be enough for the called phone to realize someone is calling them, as long as someone is in the room that is.
Have you thought about making a circuit that uses a USB sound card and GPIOs to interface an analog phone to VoIP using a Raspberry Pi?
Just use a HT502 ATA?
@@tieline1333 An open hardware solution would be nicer. Also, for a lot of individuals, they'll still need the Raspberry Pi or whatever to run Asterisk on.
Great presentation. I built it using a modified chinese 9170 module, works great except for the current source supply for the phones. Seems to work great at around 9v out of the 317, but as i crank it up to 24 the DTMF signal diminishes, stops working around 13v. I use cheap oricom tp4 phones, does the current source for this (317) need audio decoupling with a choke or filter??? I guess there is a lot of "phone guys" out there, suggestions welcome, THX Chris
Let's start with the design parameters for a POTS telephone system. About 48v DC (very well filtered, but regulation not too critical) when all the phones are on hook. Then you need enough series resistance so the voltage *at the phone* drops to around 10-15 volts when the phone is off hook (even a bit lower voltage is OK). This will make the tone generator and talk network work correctly.
The series resistance is important because it isolates the telephone audio from the zero ohm AC impedance of the power supply. In a real telephone exchange, this resistance comes from the windings of the coils on the subscriber's line relay. The coils have inductance, which provides even more isolation than a pure resistance would.
Many local office systems (PBX = Private Branch Exchange) will start with 24v DC, rather than 48v. No problem, you just need less resistance in the relay coils, to achieve proper working voltage at the off-hook telephone.
My point is that you do not need a constant current supply. You can achieve good operation with a random DC supply (must be well filtered!) and series resistance, or better yet series inductance. You do want to end up with around 10-15 volts at the phone *when* the phone is off hook.
The constant current supply is OK. When one user is talking and that one phone is instantaneously drawing less current (negative audio peak), the current will be forced into the other phone, and vice versa ... that's how the audio signal is transferred between phones. Personally, I prefer filtered DC *voltage* supply with series resistance or inductance ... that's just me, what's what the phones were designed for.
are there online stores sell this kind of project?
Awesome .
Another interesting version would be one that works with rotary phones, Instead of a touch tone frequency rotary phones sends out a pulse. An Arduino set up to read the pulse could work as the decoder.
I've thought about the same thing. In fact the Arduino could also accept input from the DTMF decoder IC, so it would work with either type of phone dialing.
Great. Tks
Oh.... I really want to buy this system. I would like to be able to build it myself but wow, this is awesome stuff and I fear I am not this level yet. I was saying to another phone modifier youtuber "I've been steadily going deaf for a while now & I got these awesome rotary phones with a red blinking light on top (I'll need two more still) that I want to hook up in all the rooms of my house so I can blink the kids and tell them I want them to come help me with something (yes people, deaf doesn't mean I can't speak anymore LOL). There are some deaf aid things like it, but it is basic tech and should NOT cost an arm, a leg, a pint of blood, and your first born for crying out loud! Honestly, the best I've found is ordered out of England and the shipping costs more than the product! Also they are ugly as sin, without even a fraction of the (finished & beautiful) look you've created. They are more like cheap, plastic junk that never caught up with modern tech (which are trying hard to prove that Deaf lives Don't matter). Maybe it could have a cool toggle switch wall panel to ring each phone! I would colour code them and all 💗💖" I really love that it is blue too... Silly, but I love it!
Thanks
This is very cool! One question: Any chance this will work with rotary phones? (I have a large house and very old phones on hand).
It wont.
Yes it WILL work but you'd need a pulse to tone converter as well.
This project is a beautiful but an error is hidden in the circuit of this multiline telephone. Here is the error: phone 4 calls phone 2 and at the same time phone 4 is communicating with phone 2, calls phone 1, phone 3.
For telephones 1 and 3 the line is occupied by telephones 4 and 2. and they cannot communicate at the moment
With this circuit only 2 telephones can be called and the other telephones are blocked until the end of the calls of telephone 4 and telephone 2
In order for it to have two instantaneous communications at the same time, the circuit should be modified.
Is there any provision for privacy , like an engaged tone when a third user tries to make a call ?
Obviously no such provision, since all the phones are normally connected together on the "party line."
it's about 110 volts in a regular phone system for ringing.
sweet thank you
What if you ring a phone that's already off hook? Would the speaker in the phone burn out?
Ah, good question that I didn't cover.. phones are equipped to handle a horrific barrage of voltages and transients that could appear on the line, including ring voltage when off hook. It just makes a clicking noise on the receiving end. If I had used an off-hook detection circuit and maybe a microcontroller, then I could prevent this from happening. But, I wanted to keep it relatively simple so that anyone could build it. Thanks for the excellent question.
@@AmRadPodcast Still a very good coverage and nice way of explaining them. Hope to see more of your videos here!
i love it
Now to grab a few cheap wireless sets and build a wireless intercom :)
can u sell it for 4 port use .. we just can buy n just link the wire only
Hi there, can I buy this kit from you?
75 mA output is a little hot. Standard lines are spec'd at 32-37. Too hot and you can burn up components in the phones. Probably won't hurt the old electromechanical phone, but those electronic phones and cordless phones won't like 75mA for too awful long.
Taking cup phones to a whole new level!
I'd love to have a set up like this. But I'm not really that good with electronics. Especially soldering. We've been buying cool old novelty phones. We just bought a house and I thought it would be cool to set them up as a home intercom. But after watching this I'm not sure that I could pull it off. It all seems way over my head.
Talk to the electronics shop teacher at your local high school. He will set you up with one of his students who would love to build this and would appreciate a little cash in return.
@@gregm.857 I don't think we have hardly any shop program at our local HS anymore. A lot of it was shut down in the 90's after I graduated and went to college.
@@looselycollected7505 Where I live, most of the shop programs have been moved out of the local high schools and into centralized vo-tech schools. Maybe your local HS administrative office can direct you to a nearby vo-tech school.
Alternatively, try the local amateur radio community. Admittedly, times have changed, and now a lot of "hams" do NOT know how to solder and build their own gear; they just buy a radio online and start talking. But there will be a few "old timers" who are proficient at hardware construction and might be eager to help you with this project.
The mechanical ringing voltage needs to be very high，maybe the mechanical bell needs 20hz. 50 or 60hz makes it dull
That's why he connected a multivibrator to a transformer.
What about a dial tone?
Good
Now it needs to be extended to support pulse dialing 😁 . .. .... ........
Just add a stepping relay, plus "A," "B" and "C" relays to control it.
09:47, Column=vertical and rows=horizontal. You said the opposite.
Not so sure about that. The ‘text headers ’ may be one direction, but I’m speaking about the buttons. Columns of buttons going vertically, rows of buttons horizontally.
how do i do this with arduino
I would recommend some diodes on your transformer to protect your MOSFETs.
Christ this is complicated. Do they not sell a plug and play system?
Can you turn digital DTMF back to analog?
DTMF is actually analogue audio.
Now make it so you can dial two phones and have two separate conversations as well. A common partyline isn't that good to have.
Pls share sch.
Can you send me one with eight telephones
Wow, that is really complicated. So, I can be really happy to be born in the 90s :D I mostly experienced VoIP. Compared to the analog way, more simple to implement a multi telephone system :D
There is nothing the least bit complicated about this project. It's the heart of simplicity. In fact you don't even need the constant current supply (TELCO systems don't have one in the speech circuit) ... it could be replaced by a filtered supply and a series resistor.
Great project, just 30 years too late! I can drop in via Alexa, ping them on WhatsApp, Life 360, ring their mobile or send them a message via Xbox live! Back in the day my parents had intercoms, which ended up getting replaced by POTS as we had a wired phone in each room. I installed Cat5e cabling in my own home, along with AppleTalk, Cat3, RG59 & generic 6 core cable, only the Cat5e cabling is still used now though...
You miss the entire point. The point is to find a "fun" use for some vintage wired telephone sets.
@@gregm.857 You have your own agenda as you clearly didn't read what I posted...
@@Fifury161 I did read what you posted. You said this project was "too late" because now you can use a lot of modern apps (instead of telephones). My reply was that this project is not meant to be the "latest and greatest" but rather it is to intentionally use some thing that is vintage. I don't know what agenda that indicates.
Can we have a ten-minute video with a random sequence of whiteboard squeaks like the ones starting at 1:33?
Caleb Bennetts yes!!!
What is that ASMR ?
DEAR SIR I WANT TO MAKE A FIRE ALARM PANEL CONVENTIONAL(4 ZONE ) HOW COULD I IT
year, steere it, drive it, ...that's right. You're insane !!!! :)))) wtf
Very interesting I suppose but the question that begs is why bother? Everyone has a mobile phone these days anyway.
Just install Asterisk
True this is definitely an option, and maybe a subject for a future video, but in this case I wanted to focus on old analog phones. I do have asterisk running on RPi which I use for daily communication - and to be honest, it's a bit sluggish.
@@AmRadPodcast you can add old analog phones to asterisk by adding a gateway.
@@AmRadPodcast npstn.us -- Uses Asterisk Systems linked together to call into vintage telephones and switching equipment, You could even connect your circuit you built into asterisk using a Gateway, Then configure Asterisk to dial onto the circuit, dial a number and connect a call. Asterisk can do Everything Analog & everything digital, It's awesome!
amps matter not volts
You can't have amps without volts.
@@gregm.857 my point was that a 10000 V charge with 1 amp will not really hurt you but a 12V charge at 100Amps will fry your - toast.
@@larrypriest5789 I'm not sure I understand why you made the comment in the first place,
and I surely do NOT agree with your conclusions.
10,000 volts will overcome your skin resistance and will go through
your body. It takes only 100mA (0.10 amps) to kill a person. So
10,000V and 1 amp certainly WILL hurt you! The usual cause of death
is ventricular fibrillation where the current causes the heart to stop
beating normally. It also usually stops respiration so asphixiation
is a possibility, and at 1 amp there will be a lot of burned tissue.
On the other hand, 12V is not enough to overcome normal
resistance of dry skin, although if your skin is wet with perspiration
(basically salt water) or you're standing in a puddle of water then
12V will go through you. And 100 Amps literally might boil some of
your internal organs due to resistive heating.
If you want a simple experiment, use your car's electrical system. It
is all negative-ground. So first put your hand on the positive
terminal of your 12V car battery ... you won't feel a thing. But if
you pull back the insulating cap on one of your spark plugs and put
your hand on the connector inside (around 12,000 V or more) you
will get a hell of a shock. And BTW I do *NOT* suggest doing this
because it *MIGHT* be lethal even if you are not grounded.
The situation that you said "will not really hurt you" has 10,000 V
times 1 A = 10,000 watts of power. The situation that you said is
worse has 12V times 100 amps or only 1,200 watts. So your "safe"
situation has eight times more power and can potentially cause eight
times more damage.
I definitely do NOT agree with your conclusion.