makeing my phone work

[Dr_Doggy]

in my home there are lost of twisted pairs that are not being used, i thought it would be fun to make some use out of this:

A)since im just starting on telephone circuits, i thought it would be fun to plug in a small microphone so that when i talk in to it people can hear me at the other end on a OFF HOOK telephone, but since my jacks are dead i will need to power them as well, has this been done before? maybe there is a circuit around to help get me started.?

B) also i was thinking about how i could plug 2 phones in so that they could talk with each other, but now that im thinking about it, i could prolly do it just by adding appropriate power to the lines, correct?

is this going to get complex? i feel like newb when it comes to ac , and i will get out there soon and find active line to hook in with scope to see what is happening when.

 

[audioguru]

A microphone has an extremely low output level. For it to be heard in an off-hook telephone the level must be amplified by a mic preamp circuit. Also maybe the telephone needs to be powered.

Two telephones can talk to each other if the telephone line between them is properly powered.

 

[Inquisitive]

is this going to get complex? i feel like newb when it comes to ac

Phones are powered by DC. They may use AC to power the charger in the base set. But, the communications of the phone function on DC.

Search for homemade phone intercom to help fill in some of the blanks.

 

[Ian Rogers]

Phones here in the uk run on about 50v But we were playing with two phones connected and powered by a 9v battery.. seem to work ok... at least the kids loved it when they were younger...

 

[Dr_Doggy]

9v and 50v is a big difference ther, im surprised power circuit is that simple, i have found intercom circuits, going to dig around there a bit!

 

[KeepItSimpleStupid]

In the US, I just put a 25 mA constant current regulator between the two. Actually, I was working on a phone and used a 600:600 transformer. Your looking at -48 V open circuit and 5V on hook.

The UK does ringing different than the US.

 

[Dr_Doggy]

i have decided that although i like a nice simple 9v+300ohm configuration, i do not like the fact that this looks to be a series wiring, arent phone lines usually parallel ?


http://www.next.gr/uploads/135-11254.png
why does this one make more sense to me, and what is the difference, besides the obvious sources?

 

[Nigel Goodwin]

i have decided that although i like a nice simple 9v+300ohm configuration, i do not like the fact that this looks to be a series wiring, arent phone lines usually parallel ?

With just two phones series wiring makes a lot more sense.

 

[mvs sarma]

without ringing interface, attached circuit would work. however ringing interface helps to keeps phones farther and really useful.

we can develop that also .

 

[unclejed613]

phones within the house are in parallel, but they are in series with the loop battery at the switch. the phones at the two ends of an active connection are in series, and in series with the battery at the switch (actually it's an over-simplification, but for all intents and purposes, it's a good way t illustrate it). two parallel phones work because they share the variations in the loop current through the battery

 

[Dr_Doggy]

ok, so the speech bridge is how telco actually does it? also i looked for ringing interface to make phones ring...
but all i could find was the circuits to decode ring.

actually this is the fuzzy from beginning... what is the circuit that telco uses to make off hook -48v, on hook9v, and ac ringer all in one??

 

[mvs sarma]

I was referring to telephone circuits used in olden days. Of late speech and ring chips have come up. but with few relays in hand we can still manage old way. The children can be better explained and they might appreciate.

The Ring is super-imposed to Party B (if ON hook), when say Party A lifted the phone, The ringing voltage could anywhere between 15 to 60V and 25Hz sine /square wave. it can be with interruption breaks, during which period on hook status of called party can be sensed. Once OFF hook, the ring circuit can be tripped, and the entire arrangement can be for speech across.
In real situation the exchanges feed 50V dc on like with current limits on both the limbs designed at say 35mA. thus taking the copper loop resistance into picture, the voltage measured at Customer premises would be around 25V for longest distance, and 35V or so for short distances from central office, while OFF hook. wile they implement constant current mechanism with dual transistor circuit, we can just use resistors and limiting elements. we can also have a Opto coupler in series with current path, whose output at transistor gives us the on/off hook status.

 

[KeepItSimpleStupid]

Here is a company that makes a ring generator. **broken link removed**

In the US, there were different ring frequencies used in "party line" configurations. This is where many people share the same line, but the ring signal changes to ring the specific houses. I found this one http://www.camblab.com/home.htm using "telephone ring generators" for a search.

Telephone simulators are traditionally expensive because of DTMF and Caller ID and measuring the stuff that makes the phone system work.

REN (Ringer Equlivelency Number) determine how many bells a line supports. The REN's are added.

The BT system should be a lot easier to inbterface because the ringing signal is separate. I believe there is a capacitor in the jack.

Modern ringing interfaces (detection) are done with optocouplers.

You may sfind some stuff using "Data access arrangements" or DAA for a search. http://www.google.com/url?sa=t&rct=...Gu44Fw&usg=AFQjCNEIMJBFKBsN71KINR-h60nPS-b8PA

I had in my bookmarks, (lost) a device that would ring the line whan the phone was picked up.

I can't find what I'm looking for: http://www.telephonetribute.com/telco_line_simulators.html

There is a device that when the phone is picked up the other one rings. Here is one: **broken link removed**

BUT remember, the BT system is different than the US and BT is a lot more restrictive than the US. The ringing signal being separate is the major difference.

In the US, we are responsible from the demarcation point (called the NID or Network Interface Device) which is usually mounted to the exterior of a residence. We get to maintain the inside wiring. Early (1950's) houses were wired with quad wire and later power was supplied on two of the wires for lighted dial phones (Princess).