Caller ID Decoder Project

hbl2013

Senior Member
Has anyone ever tried to build a Telephone Caller ID system? I would like to have one to be able to screen telephone calls and it would be a good PICAXE project.
Any comments or suggestions?
 

premelec

Senior Member
I collected a pile of the stand-alone ID units at yard sales thinking they might be good for displays... however looking into the signal coding [on Internet] I decided it's too much trouble... that said where I live you must pay to have the telephone line CID signals come through - they aren't transmitted to everyone - I haven't subscribed... I seldom answer the phone without screening on an old answering machine :)
 

papaof2

Senior Member
The most useful phone addition I've found is made by Phillips - it's a talking caller ID box. It speaks the number by default, but you have the option of putting in a name or other info in 15 seconds of your own voice - for up to 100 numbers.
I can screen all calls without having to look at a handset display.
 

hbl2013

Senior Member
I have Caller ID on my land-line phone, and it will display the caller, if they allow it. And that is the problem. I get too many unindentified calls, (allthough I am on the Do-Not-Call list) and I like to dump them ASAP.
Here is were a Caller ID processor would become handy, it would be able to screen the call and hang up on any one who would meet a certain creteria. Or, on the other hand, could alert me to calls that are important to me.
I understand that the Caller ID info is transmitted in a serial fashion in between ringing signals, but before I go and investigate it, I like to see if somebody else has done the work allready. No sense re-inventing the wheel!
 

RexLan

Senior Member
I have Caller ID on my land-line phone, and it will display the caller, if they allow it. And that is the problem. I get too many unindentified calls, (allthough I am on the Do-Not-Call list) and I like to dump them ASAP.
Here is were a Caller ID processor would become handy, it would be able to screen the call and hang up on any one who would meet a certain creteria. Or, on the other hand, could alert me to calls that are important to me.
I understand that the Caller ID info is transmitted in a serial fashion in between ringing signals, but before I go and investigate it, I like to see if somebody else has done the work allready. No sense re-inventing the wheel!

That's called Google Voice and it is FREE
 

Buzby

Senior Member
By far the easiest way to build a Caller ID box is to use one of the 'off the shelf' IC's that can decode the data which is sent after the first ring signal.
Just Google for 'Caller ID circuit'.

There may be other issues though, depending on where you live it might not be legal to build your own device connected to a telephone line.
 

hippy

Senior Member
Easiest way is to find an external modem which supports caller ID then you have no worry about connecting to the PSTN system nor equipment approval and interfacing should be straight forward RS232 serial.

Second best bet might be a caller display from which you can remove any existing micro and display and use the interface plus the CID chip if it can be identified.

There are a number of different caller display triggering schemes which may or may not matter. You simply need the right line interfacing but there may be issues of type approval in that.

I worked on a CID system for phones in the American market some years ago but cannot remember the details. I recall it was easy enough receiving the CID data but line interfacing and circuit design was already provided. I've no idea which CID chip was used.
 

Buzby

Senior Member
Yes, as hippy says, many 'old skool' external ( or internal Winmodems, like mine was ) provide caller ID data on RS232.

I experimented years ago with a Winmodem 14400 ( 2400 baud ) modem ISA board, which provided Caller ID, but we didn't have Caller ID at the time, so I never looked further into that aspect, I was just decoding DTMF.

Using a ready built interface, like a modem, will get you (a) a working front end, and (b) no trouble with the authorities.

Cheers,

Buzby
 

MikeAusP

Member
Here are some useful resources

General
http://en.wikipedia.org/wiki/Caller_ID

Technical
http://melabs.com/resources/callerid.htm

Modems
http://www.ainslie.org.uk/callerid/cli_faq.htm#Q_18



Transmission at 1200bps makes it easy to read from a PICAXE. Fortunately the data stream has a fixed-length format that will make it easy to decode (from Ref 2)

"Here is an example of a SDMF message. Each byte is in HEX.
04 12 30 39 33 30 31 32 32 34 36 30 39 35 35 35 31 32 31 32 51

04 - message type word - 4 indicates SDMF 12 - 18 decimal, number of bytes in date, time and phone number 30,39 - 09, September (ASCII) 33,30 - 30, 30th day (ASCII) 31,32 - 12, 12 hour (ASCII) 32,34 - 24, 24 minutes (12:24 PM) (ASCII) 36,30,39 - 609, Area code (ASCII) 35,35,35 - 555, prefix (ASCII) 31,32,31,32 - 1212, sufix (ASCII) 51h = Checksum Word

Thus, the CID string can be summarized as follows:
The message is in SDMF format, consisting of 18 bytes of information, not including the checksum. The call was made on September 30 at 12:24pm. The calling party's phone number was (609)555-1212."

Yes . . . I did spend my working life with a Telco.

Mike
 
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hbl2013

Senior Member
Thanks fellows for the replies. It gives me enough leads to look into. I was not aware that there were chips available that would do most of the work for me, I have to look into that. (Update - I did so, eBay lists several of them from China)
One of the problems I can see is how get a test signal to see if things are working as they should. I really hate to have to build a complete Caller ID generator just for that, but I guess it could be done also with a PICAXE chip given the information from MikeAusP. Or I could call my landline repeatedly from my cellphone(!)
 
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