WebAudioPhone

A summary of functional blocks of a phone , modem and Text Phone

Some diagrams:-

simple intercom:

A TDM telephone system can be summarised by this diagram, where the codecs are clocked at multiples of 8kHz sample rate. Jitter buffers were used as well.

Hybrid using a transformer, similar to that used in GPO dialphone:-

Using Wheatstone bridge hybride model of phone network:-

http://www.dougrice.plus.com/dougnapTheory/indexFurtherNotes.htm

Textphone functional diagram:-

Textphone, used keyboards and UARTS and modems to send the typing over the 2-wire Telephony :-

and Textphone, used modems UARTS and displays to display the typing over the 2-wire Telephony :-

 Summary of a 2-wire Phone:-

 - X  - Switch controlled by microcontroller in phone.

 phone line -- [ Hookswitch ] - X - [ bell / alerter ]
                                X - Caller ID -- [ display ]  
                                X - To Hybrid   

 [ dtmf keypad ] - [ dtmf  IC  ] - X --|
 [ microphone  ] - [ audio     ] - X --|
 [ keyboard    ] - [ modem     ] - X --|
                                       |-- to Hybrid 

 from Hybrid --|
               | -- [ audio         ] - X - [ loudspeaker / handset ] 
               | -- [ modem         ] - X - [ display   ] 

http://www.dougrice.plus.com/dougnapTheory/index.htm has notes about 2-wire phones and Hybrids

https://www.britishtelephones.com/diagrams/n846.pdf has the circuit for phone and explains the hookswitch.

The hook switch used to connect the Bell circuit across the line until the User picked up the handset.

The bell was AC coupled to the phone line. When the user picks up the handset, The phone draws current.

With the handset off hook the hybrid circuit was connected to the phone line.

The line current powered the phone and signalled that the phone was off hook.

Modems that plug into a phone line have a similar functional block diagram.