DTMF dial tone

[lerameur]

using a modem is a good idea, plus I have a few of those 33.3 external modem laying around. just have to figure out how to hook it up to a pic but that should be too hard. thanks

ken

[Josuetas]

It can´t be simplier than this,

By the way those modems you have must surely have the transformer you need.

Now forget about the ugly picture!

Pay attention to this fact: the line will remain Off-hook as long as it is connected to the
transformer, you might need a relay to disconnect the line from the Transformer.



DAA is the device that implements this transformers with silicon, it also gives you more functionality like ring detection and off-hook switch. It might be more expensive than the simple schematic, wich by the way complies with all requirements of ITU.

[mvs_sarma]

Actually the pic should be switched in to the circuit only when you want to make outgoing call - or after the predesigned circut arranges for answering the call thereby stopping the ringing current (75V /20to25Hz_superimposed on the 48 Dc as already mentioned by b1arrk5.

So therafter no fear of high voltage as the current starts flowing on the telephone line.

[b1arrk5]

Ken,

Take a look at the Serout2 command in the manual, around page 144. All you need is a connector for your modem and a 1K ohm resistor! The modem will accept 'Hayes' AT commands. After you set up your oscillator and other defines per the manual just enter SEROUT2 PORTA.1,84,["ATDT 555-5555"]
and the modem will go off hook, wait for dialtone, and dial the digits. You can try it out first using Hyperterminal or another terminal program. The AT stands for 'Attention', and if you just type AT your modem should answer OK. You can find a lot of pages with all of the AT commands on the internet, but not all modems will implement all commands.
If you want to get a little fancier, use a MAX 232CPE chip with your PIC, and then you can send and receive, there are a lot of examples around. I use a LabX board from MeLabs for my development work, and it is hooked up to a modem, I use it all of the time to turn some lights on when I work late so I don't come home to a dark house.

Jerry.