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Need help building a doorphone intercom

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pasosh

New Member
Hi

I am looking for schematic/idea how to build an intercom panel for my home telephone switchboard.
i have one free extention as a panel extention.
what i need is, a circuit that upon pressing the call button this circuit "open" the mic and speaker and generate a dtmf tone (like "0")
this acion will ring to the telephone switcher and someone who pick up the phone can speak freely to the panel.

i hope i explain my self right :)

Thanks

pasosh
 

plouf

New Member
looking for same think still none with an idea ? (5 years... of thinking ;))

basically i have panasonic doorphone for PABX
BUT because we switch pabx froms ISDN to PSTN old PABX
was panasonic and new one isnt .
so i thinking to modify or adapt or Create a New One using PArts of older
(plastic case speaket etc)
 

audioguru

Well-Known Member
Most Helpful Member
I don't know if DTMF dialer ICs are still available. Take one from an old phone and use it to dial "0".
Then buy a telephone doorphone or make one.
 

plouf

New Member
supposing i find a DTMF chip

how do i make it auto-hook-up when button is pressed ?
and hook-off when conversations is end ?

rest i believe are easy...
 

crutschow

Well-Known Member
Most Helpful Member
I have a Doorbell Fone (as at "doorbell fon" - Smarthome). It rings your phone when someone pushes the button and you can talk to them from any phone to the doorbell mic/speaker.

Will that do what you want?
 

audioguru

Well-Known Member
Most Helpful Member
You need to do a tew important things to make your own door-phone:
1) Go off hook before you dial.
2) Hang up when the conversation is finished.
 

plouf

New Member
actually thats what i am asking
how to do on and off-hook

i can take a cheap telephone obviously
 

audioguru

Well-Known Member
Most Helpful Member
I don't think your home telephone system is designed to use a door intercom.
 

plouf

New Member
I don't think your home telephone system is designed to use a door intercom.
It's NOT

(i know ican explain too well in english anyway)
The thread reach a point which actually i just don't know how to control
the hook (to make it on-off) and all the rest are easy.....
 

audioguru

Well-Known Member
Most Helpful Member
That site (from India?) has circuits that are 40 years old and older.
A few of their circuits worked before the parts became obsolete.
Go to India to buy the parts.
 

Mikebits

Well-Known Member
Well, the site seems to be hosted in Lansing MI, but regardless, who cares where it is from? What is wrong with India many fine engineers hail from there? I was just trying to help. Instead of just adding negative input, perhaps you might suggest why the project is not possible or why it would be so difficult to do.
 

audioguru

Well-Known Member
Most Helpful Member
I don't like seeing very old circuits posted from India today. The old circuits use obsolete very old parts and the circuit might not work anyway. This is 2008, not 1968.

The American website just copied the very old circuits from India. There are at least two websites in India with exactly the same old circuits.

I worked with telephone systems 28 years ago when the government in Canada said that BELL must not be the only supplier. Some cheap telephone systems came from Korea and were horrible and others with distributed processors came from Japan and were pretty good except for software problems.
I watched Northern Telecom telephone systems go from multiple pair cables (50 pairs) to digital (2 pairs).

I worked with an excellent quality multiplexed large intercom system from Norway.
 

Ron1406

New Member
Hello Pasosh,
Did you find a sollution for your problem here? It is almost 12 years later since you started this topic... As I'm looking too for a schematic diagram for building a doorphone , connected to a phoneline. Generating a number and take the hook off isn't a problem , it is easy build with an AVR controller. For me the problem is to have a decent microphone amplifier , connected together with the loudspeaker amplifier and then connected to a 600 ohm transformer. As when the microphone pics up some signals , it would be advisable not to amplify these sounds then and yet , they both need to be connected together to reach the telephone line. Can you help me here?
Many thanks,
Ron1406,
 

rogs

Member
For me the problem is to have a decent microphone amplifier , connected together with the loudspeaker amplifier and then connected to a 600 ohm transformer. As when the microphone pics up some signals , it would be advisable not to amplify these sounds then and yet , they both need to be connected together to reach the telephone line. Can you help me here?

Most 'doorphones' use 3 wires, which can give you full duplex (simultaneous two way) speech, using a differential audio drive to reduce the audio level between the microphone and the speaker in the same unit.

Like this circuit: http://www.ecircuitslab.com/2011/06/full-duplex-intercom-circuit.html

You can't do that with only a two wire circuit (like a telephone)

You will need to use a 'semi duplex' technique for that, which can be built using a device like this:

http://cache.freescale.com/files/timing_interconnect_access/doc/data_sheet/MC34118.pdf

That particular IC may be hard to find now, but that data sheet shows the technique needed for two wire systems.

If you can use 3 wires, it's so much easier to solve the local microphone/ speaker feedback problem....
 

dr pepper

Well-Known Member
Most Helpful Member
Pasosh never replied to any comments 12 years ago, I dont think he's comming back.
 

rogs

Member
No -- but the same thing keeps coming up. Folk who think you can use a mic and loudspeaker on a phone line, without the need for semi duplex attenuation.
The extra cable 'core ' used for regular door intercoms makes all the difference.
Electronics move on at rate of knots. The laws of physics (and acoustics) do not.....So there's always a new generation who don't get the 'feedback' issue straight off...
 

dr pepper

Well-Known Member
Most Helpful Member
Nifty circuit in the first link.
I know a farmer who uses a couple of standard 'phones with a dc supply as an intercom from his farmshop to the office, 'calling' is done by rattling the hook switch, the resulatant pulses sort of rings the ringer in both 'phones, this little circuit would be a major improvement, a nice mod would be to power the remote unit via the co'ax.
 
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