recreate telephone system for intercoms

[awwolfe]

I have several intercoms in my house that were tied into the telephone system so that I could use any telephone to hear or answer someone at the door. However, I've dropped my telephone company and am only using a cellphone now...needless to say the intercoms do not work anymore.

What would be the best/easiest way for me to create something that would recreate the tone-signal-voltage needed on the telephone wires so that the intercom system could work again?

Thanks,
Tony

 

[timothy48342]

I did this a few years ago, but I don't remember everything about it.
(Search for "make intercom from old phone" and there is a lot of info out there.)
Doing a quick search, I saw some circuits with 10 or 20 components or so, but it is much simpler than that.

This pic...

from this website:http://www.schoolholidayprojects.com/telephoneintercom_project.html
...shows exactly how I wired mine. Real, real simple, huh?

The only thing is they say 9V to 12V and I think I used more. They say you might need a resister, too. I don't think I used one. I may have gotten lucky and picked two phones where one or both had some proterction built in. Also, I was using about 50 feet of phone wire for the connection, so that could change things. Also my power supply might have not had enough power to destroy things.

Oh, and one thing... You do not need a tone for them to work. You just need the right voltage and available current on the line. (And there is a wide margin of voltages that will work.)

--tim


Making them ring is a little more difficult. The phone company sends a higher voltage an/or higher amperage signal down the line and the phone responds to that. (I don't remember if the voltage changed or the available amps) It is actually that signal that powers the ringer. I never got mine to ring.

 

[timothy48342]

Oh! And I don't what happens for more than 2 phones. It seem to me that if the 3rd phone was hung up, then it would prevent the first 2 from working. (That's if they are all in series.) If they are all parallel, (or if even 2 are parallel) it seems like they wouldn't work at all.

I know when they are all plugged into the house, they are all parallel, so maybe that is the way they are supposed to work.

Now, I'm thinking maybe there was a better way to do that. But the way I did it worked for the 2 phones. It worked on the first try with the first power supply I grabbed and wired up, so I never thought about it again.

-t

 

[awwolfe]

Thanks for the response. I am not sure this will work for me, because I already have the exterior intercoms wired and am trying to use them with the existing telephone wired into the house. So setting up a 2 telephone intercom system isn't exactly what I am trying to accomplish....However, it might be a start if I can get it working then try to tie in the exterior ones.

What I was thinking of is using a small 12v transformer and splicing it into a phone cable plugged into a phone wall outlet (green and red as in drawing). Any issues or thoughts before doing this? I've only half thought it through.

 

[timothy48342]

I'm not sure what it would do? Just a transformer? I think I would test it on just one phone first. One phone that you don't mind destroying.

12V is within the reasonable range for the phones. I assume you mean a powed transformer with a 12V DC ouput. (A Wall Wart) You could even start as low as 9V for testing.

I opened one up last night and noticed one thing right off. Both leads, (red and green) coming in have a resistor on there. I'll try to read the color bars and so we know about what it draws.

The next things after the resistors is a full bridge rectifier. I still think the aidio signal rides on DC. The rectifier might have something to do with how the ringer works.

I decided to try and trace the PCB to get a schematic. I need to get better at that. In this case there are only about 11 components and no surface mount, so I think I can do it.
(Also this is a schematic I want to have. Ya know, for posterity.)

Here is what I have so far. This IS WRONG! (but close) All the components are presents, but I am missing a connection or 2, and I haven't really started indentifying component values.

I was wondering though. How does the existing intercon work? Have you tried to see what kind of singal goes from consol to consol?

Intercom make and model might help, too.

--tim
Edit: RE-read you first post. Your intercoms worked fine being plugged into the phone system, so they work like phones without a ringer.

If you destroy an intercom, can you replace it cheaply?
I think I would try it on just one old phone first and then see if that phone still works as a phone or is damaged.

Then if all is good, try 2 phones in parallel. (NOT like in my first picture/link) You need it to work in parallel, since that is the way the whole systems is wired.

I don't think I would just hook it up to the whole system right away. Too risky,
:endEdit

 

[awwolfe]

Seriously appreciate the responses. My lack of knowledge on the issue thought it would be simple enough to recreate what the telephone company puts out and then everything would work. I found these install instructions on the intercom system if it would help anyone help me....sorry I didn't find this and post with the first message as now seems obvious I should have....

http://www.smarthome.com/manuals/5070c_user_install.pdf

 

[awwolfe]

after some more searching I found this....

http://www.homephone.com/support.htm

 

[BobK]

This might help. It shows what the telephone company would put on you phones. 48V plus some inductors and resistors.


http://www.epanorama.net/circuits/teleinterface.html#general

bob

 

[timothy48342]

I don't think you need to supply a simulated phone line for this. I don't see any reason the DoorBell Fon even needs to connected to an outside phone service to work. Obviously, you won't get a dial tone and you can't make calls, and might act a bit strange if you try to activate call-waiting, but everything else should be fine without it.

Does the power-on LED on the Door Box Controller light up?

--tim

 

[awwolfe]

Yes the lights on the box controllers light up. I've been checking the voltage output of the lines going out to the phones and to the boxes and they are not as described in that previous document link. Which may mean the controller is bad. However, while possible it would mean it went bad at precisely the same time the phone company was disconnected, which is challenging to fully believe the coincidence (not to mention I'd have to pay for a new controller).

What I get....
Out to phones: (~8v steady---does not change when intercom button(s) are pressed)
Door 1: ~17v when button is not pressed, ~12V when button is pressed
Door 2: ~2V when button is not pressed, ~0.6V when button is pressed

Any other thoughts?

Are there any other simple solutions, anything I could build myself ( I can do basic stuff) to use the external intercoms and at least get a chime or something to go off...I would rather use the phones to ring, even if can not get the speakers to work (although that would be nice as well)

Thanks,

Tony

 

[awwolfe]

BobK,

Thanks for that link, very informative. I'm looking at it now and see if able to recreate. However, the issue that the voltages out from the controller are different worries me a little so will pursue that end first.

 

[timothy48342]

Having different voltages at the 2 Door Stations is no good.

You might want to disconnect the "door 1" and "door 2" wires and test the voltage at those screws on the black box. (Lable the wires so you know how to reconnect them.)

If you get significantly different voltage at the "door 1" screws on the black box compared to testing at the Door Station, then you have a wiring issue. Same for "door 2" screws compared to Door Station 2. Also, I would think the voltage at the "door 1" screws and the "door 2" screws would be the same.

There was a test I saw in the manual that you should try:
"""
Step 2- If you are not able to access the door with the "flash key then go to the DoorBell Fon controller (black box). short the two screws of the door position (very fast). If the phone rings then check the wiring between the door station and controller
"""

I would do this with the "door 1" and "door 2" wires disconnected from the black box, so the Door Stations don't interfere.

Also disconnect the "line in" phone jack in case there is a problem with the phone companies line.

Disconnect the "line out" jack from the house phone lines. (There should be nothing connected except power at that point.) Just plug in one known working phone into "line out".

Then briefly short the 2 screws for "door 1" or "door 2" and the phone should ring. (Try each seperately.)

If it doesn't ring, then it sounds like a bad controller. (or a bad phone. Double check that the phone works at some other house if that happens.)

If it rings, then it might be ok. Well have to come up some more tests.

One of those tests should narrow down the problem, though.

--tim

 

[timothy48342]

...
I would do this with the "door 1" and "door 2" wires disconnected from the black box, so the Door Stations don't interfere.
...

Opps, I don't like that test. We don't know if the controller can detect the Door Stations. It is fine to do that anyway, but if the phone doesn't ring it's not conclusive evidence that the controller is bad. You might have to have those wires connected to get it to ring.

But I am sure that you don't have to have both sets of wires connected, since some people won't even use both. So test with one pair connected at a time. (Especially since that wiring has suspiciously different voltages.)

--tim

 

[awwolfe]

I took off the 2 sets of wires leading to the intercoms...~4.3V (good) on both.
I connect the intercoms (1 at a time) and goes to ~2.2V (good) on both.
To phones (~0V)

I press intercom 1 button and hear an audible click on the controller (like a small relay) door 1 goes to 17V (good), but then stays at 17V even after button is released, to phones stays at 8V. Same thing when done with door 2.

Also, I recruited some help and got someone to talk at the intercom and I can hear them on the phone after they press the button...but no ringing from the phones and no voltage 'spike' like 28v or whatever is needed to make them ring.

Thanks again for the responses, seems like it is 'sorta' working, but just not quite...
Tony

 

[timothy48342]

Ok, good work. (I mean good description of your test procedure. Ya know? And also gratz on some success!)

(I'm just going to think out loud here)
Voltage is the same for both doors at the attachment screws. That's good.

The ~17V you first tested at door 1 might have been because the button had been pressed recently.

And the ~2V at door 2 compared to 4.3V at the box seems like a big drop, but we don't know the resistance of the wiring and we don't know how much current the door stations pull, so that may mean nothing. Although ~0.6V at door 2 when the button was pressed may indicate bad wiring at door 2. It should have jumped up to near 12.

I think the door intercoms may work like this. They get a small voltage level when not in use that is just enough to let the controller tell when someone has pressed a button. But the door station needs more power to fully function, so voltage jumps to 17 while your talking. That 17 probably drops back down after the phone is hung up or after some specific time. Door 1 sounds like it is working fine.

And you can hear them. Great. Yeah, that's a lot of things working.

So why isn't the phone ringing? hmm.

Questions:

Did you use just one phone connected directly to the "line out"?

Do you know that phone rings fine? You can plug it in somewhere and call it? There is no "ringer-off" switch? (LOL)

The manual mentioned that each and every phone has a REN number printed on the bottom. (None of my phones have that!) It says to add up the REN numbers of all your phone and it can't be over the number listed in the manual. You don't need to do all that. Just understand that the controller (when working properly) can only put out so much power for the ringers of all the phones connected. If too many phones, then no ring. BUT ALSO, if you have some bad wiring and a partial short somewhere in the house, that could simulate the same thing as having too many phones.

So make sure your trying to get a ring with just one phone and not the whole house and try a couple different phones. You might also want to leave door 2 disconnected for now and just test with the door 1 button.

The fact that you get a stable 8V on the phone line when you press a button might sound like your not getting the ring, but I don't know for sure. If the controller has a way to detect that no phone is plugged in it might refuse to send the pulse for safety.

So do the test with the phone hung up and plugged into the "line out" jack. If you want to put a meter on there at the same time, you'll can use the "line out" screws for that.

You could do this test by pressing the button on Door Station 1 OR by briefly shorting the "door 1" screws. That way you don't need a helper to press the button while you listen for the relay and watch the meter. (whichever is easier or try both ways.)

So, rigerous ringer testing procedure:
1 One known good test phone.
2 (A seconds known good test phone in case there is something freaky about the first)
3 On the hook and plugged into "line out". Meter on "line out" screws.
4 Nothing connected to "line in" jack or screws.
(Not connected to the phone companies line OR the house phone wires)
5 "Door 2" disconnected.
6 You somehow know for sure that the test is being conducted.

I think that's it. I imagine you did the test similar to that. I'm just trying to be absolutely sure there is not something making this controller look bad when it's not.

If it still doesn't ring well, then, I don't know right now.

Describe everything you do real well like you did before.

--tim

 

[awwolfe]

Ok, major progress thanks to Tim. Instead of using the to phones screws, I instead plugged a single phone into the to phones jack. I got a phone ringing! and intercom worked as expected (could hear until hung up). I am not sure why the to phone screws went bad, but at least I won't have to shell out $$$ for a new controller (unless the to phones jack goes bad )

Today, I'll try to run the phone jack into my house lines and see if I can get a phone in the other room to ring, but feeling much better at this point....thanks to all who read and commented and special thanks to Tim for taking the time to help me out.

Tony

 

[timothy48342]

Ok, major progress thanks to Tim. Instead of using the to phones screws, I instead plugged a single phone into the to phones jack. I got a phone ringing! and intercom worked as expected (could hear until hung up). I am not sure why the to phone screws went bad, but at least I won't have to shell out $$$ for a new controller (unless the to phones jack goes bad )

Today, I'll try to run the phone jack into my house lines and see if I can get a phone in the other room to ring, but feeling much better at this point....thanks to all who read and commented and special thanks to Tim for taking the time to help me out.

Tony

Booyah!!

-tim

 

[timothy48342]

Tony, I just thought of something...

When you get to start working with the house phone wiring, the first thing to check might be at the junction box where all the lines come together. You said this happened when the phone company turned off the service. I wonder if maybe they messed with the wires, like disconnected them all or just snipped them. (and if it turns out this was the problem all along....ugh)

Junction box is a good place to start looking for a fault, anyway.

Gratz, again.
-tim