Hi. I haven't been on the forums in awhile, and I've been working on an Arduino project. Well I'm wondering how I can include DTMF into my project. What I would like todo is called my Arduino from any phone, input a code, and after the code, input a number to trigger some other part of my code. Is there some way I can do that and just tie it strait into my phoneline at home?
You want your Arduino to decode DTMF?
This would be a good reference: http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=62995
I got a fair number of hits searching these forums for "DTMF" and "Goertzel" too.
The electrical interface from POTS to the Arduino would take some thought also. The local loop is a 48V current loop and you will need to cook up a transformer coupling I think. Are you going to have to receive and decode ring indication, off-hook on another extension and handle pick-up and hang-up too? There's lots of info how these things work. Google is your friend.
You can get IC's that decode DTMF signals.
Try to check this:
http://www.siongboon.com/projects/2005-07-18_dtmf_circuits/
It's not Arduino, but you should be able to see how it can be done
You need a DAA to "legally" connect to the phone line. Cermetek makes some modules and you can probably find cheap ones on ebay but what I did was scavenge one out of a phone that showed up on the curb one morning. Most everyone has a defunct POTS phone or maybe a defunct answering machine that they can take apart.
So of the stuff your talking about, I can't understand 
You have to be more specific than that.
What don't you understand.
Pretty much just this:
DAA "legally"
POTS
Sorry, a DAA is a "data access arrangement" and it is necessary to isolate your circuitry from the phone company's wires. The two wires at your phone wall plug are called "tip" and "ring" from the old days when operators made circuits by plugging patch cords in a big panel. The plugs look like, well, phone plugs. 
The DAA takes tip and ring from your wall and converts it to two sets of differential signals for transmit and receive, TX+, TX-, RX+, and RX-. You also get a pin that goes low when there is a ring signal on the line and another that you take low to seize the line for an incoming or outgoing connection. There are more pins but those are the important ones. You can buy a DAA or you can build one (google it) but you can also find one in some old phone equipment When my nephew wanted to make a phone patch for his ham rig, we found one in an old phone.
As far as DTMF goes, dual tone multifrequency, you can buy a decoder chip or probably find where someone has already written an Arduino sketch to do it.
POTS: Plain Old Telephone Service.
Any clearer?
Sort of.
EmilyJane:
POTS: Plain Old Telephone Service.Any clearer?
Excellent (and informative) reply!
What if I took apart a Fax Machine or a Answering Machine? I'm sure it would work.
Do you know where I can get a 8870 IC Chip?
What I would like todo is called my Arduino from any phone, input a code, and after the code, input a number to trigger some other part of my code
You can also do that if you use the browser on your phone. In this case, all DTMF stuff on Arduino side will be replaced with an Ethernet. There are lots of examples on the latter.
Do you know where I can get a 8870 IC Chip?
Soapy29:
What if I took apart a Fax Machine or a Answering Machine? I'm sure it would work.
Just about anything that connects to the phone lines has a DAA. An old modem card or as you suggest a fax or answering machine.
chiming in late here, but I've done DTMF with an 8870. I was interfacing to a radio, not POTS, so my schematic has no POTS interface.
Here's the old forum post .
-j
[edited, I posted the wrong link the first time]
We'll I could do it with a radio. Actually, I was just looking at how to build one So how can I build an FM radio broadcaster that broadcasts a DTMF tone, and on the other end have a homemade receiver with the 8870 chip decoding the sound into binary data for the Arduino can read. I can use Skype on my iPod for the DTMF tones, but how do I build everything else?
I found this on Google: http://sci-toys.com/scitoys/scitoys/radio/am_transmitter.html
So how exactly would I build a radio to match this one?
That's a medium wave transmitter, if I'm reading it correctly - you should have one around, somewhere.
AWOL:
That's a medium wave transmitter, if I'm reading it correctly - you should have one around, somewhere.
What do you mean I should have one laying around?