I still have a good old landline at home. But I miss the easiness of cell phones where you can just see a list of missed calls. I'm a MSP430 Launchpad hobbyist and I'm alway looking for some little projects. I wonder if there is a way to tap my own landline and listen for calls. This should be passive listening, so no need to answer the call. I'm living in Belgium, is the signal on our lines encrypted?
Electronic – Landline listening
microcontrollermsp430telephone
Related Solutions
You can get a transformer from an damaged modem, like that:
Reminder: In my country (Brazil) it is forbidden to record a phone conversation without the consent of another person on the phone.
Here is a project that someone did a while ago that seems similar:
http://brohogan.blogspot.com/2009/12/telephone-interface-updated-123009.html
He details the DTMF chips he used and gives a sample sketch and schematic. But he also brings up some potential legal issues.
I think given the legal issues and the interface issues (synthetic voice, Morse code, etc.) I would go with a cellular interface and use text messaging to talk to the system. In which case Sparkfun has a bunch of stuff to do just that including an Arduino shield that accepts a SIM card.
http://www.sparkfun.com/products/9607
I'm in the planning stages for a cellular project and this shield seems like a really nice solution for prototyping. And they offer the standalone module as well.
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Best Answer
In the U.S., an incoming call would start with ringing, which is an AC signal of around 60V, then proceed to a modulated Caller ID signal after the first ring. It could be similar in Belgium.
So it would take some dedicated circuitry to handle and detect the 60V ringing and then decode the Caller ID. It is messy in the sense that you have to handle the 60V and the plain old telephone scheme of things. If you do a search on Caller ID circuits, you would find lots of information, most of them old.
Recently, I put together something to monitor incoming call with my computer. What I did was to buy an USB telephone data modem (I got mine from Ebay for $10). The modem would handle the interface to the telephone line. The Modem's USB connection would appear as a serial port to the computer software. The software would use the serial port communication to initialize the modem (using the "AT" command set) and then to receive the caller ID information.
To have a modem interfaced to a MSP430, you probably need to use the RS232 type serial interface (not the emulated serial interface through USB). Nowadays, the only serial port modem available might have to be an old used one.