IPABXwPP (Intelligent Private Automatic Bi-eXchange with Privacy Phone) is a small devices for use with TeleDanmark's service called 'distinctive ringing' (in danish: Nummer-bestemt ringning).

It gives the possibility of getting one or two phonenumbers attached to your primary number.
Calling the 2nd (or 3rd) number will generate a different ringing-pattern, making it possible for the user to know (by listening) which number is called.

It's perfect for subscribers having kids (which can get their own number) or wants another number for their fax-machine/modem. When the phone rings, it's possible to determine which person should answer the phone, simply by listening to the pattern.

The price for this service is (at 13.03.98) 40DKr every third month.

The problem with using the service, is that even though the phone-call is for the kids (or the fax), it's still ringing all over the house. This is where the idea for IPABXwPP came up.

Features:

• IPABXwPP has one input (the phoneline from the local exchange), and 3 outputs (one for each different ringing pattern). Whenever a call occurs, IPABXwPP measures the pattern, and switches on the line, which the pattern is assigned to (or rather, switches off the lines which shouldn't ring).
• Each line has "Privacy Phone", which means that only one line can be offhook (phone in use) at a time. The other lines are simply switched off during calls (very usefull when using a linequality-critical modem).
• A LED shows different 'states' (phone in use, incoming call, last called line etc.).
• Let's CLIP-signals pass-through (if you have a CLIP-device (nummerviser) hooked up to one of the internal lines, you can still view all incoming numbers).
• Turns on all lines after 30 seconds of ringing.
• Let's 'notation-ringing' (privat-notering) pass through to all lines.

TeleDanmark is probably not the only Telephone-company offering this service, so it should be possible to use IPABXwPP in other countries than Denmark. (The software might have to be changed a little).

The ringing patterns:

Normal ringing:
Ring    -------                                     -------   750ms+/-20%
Pause          -------------------------------------       --7500ms+/-20%

Notation ringing:
Ring   ---   ---   ---   ---   ---   ---   ---   ---   ---    330ms+100ms/-10%
Pause     ---   ---   ---   ---   ---   ---   ---   ---   --- 330ms+100ms/-10%

Distinct ringing 1 (typically used for telefax ringing):
Ring   ---            ---            ---            ---	      300ms+100ms/-10%
Pause     ------------   ------------   ------------   ------1200ms+100ms/-10%

Distinct ringing 2 (Voice-phonenumber #2):
Ring   -----       -----       -----       -----       -----  500ms+100ms/-10%
Pause       -------     -------     -------     -------     - 700ms+100ms/-10%

Deviations:  ex. 500ms+100ms/-10% = 450->600ms

Detailed description of operation:
The hardware is built around a PIC16F84 (PIC16C84, or any other 16Cxx) or a PIC12C508 (any PIC16C5x), and contains only a few external components. The oscillator-frequency on 4MHz (when using a 16F84) was chosen because it's widely available.

The Privacy Phone is implemented in software (turns off 2 lines, and checks if still offhook, if not, tries another combination of 2 lines until it determines which line is in use). It takes about 50ms, and is not noticeable by the user.

Ring-detection/offhook detection is implemented with a couple of resistors and some zener-diodes, and decoding is done in software.

The LED lights whenever theres an incoming call, and it flashes (short) in the normal state. If the phone is in use, it flashes slow. Fast flashes show whish line was called last (1 for diff. line 1, 2 for diff. line 2, and 3 flahses for the normal line).

I have drawn a PCB for the PIC12C508 version (components layer). As the circuit is fairly small it's also easy to build on a piece of veroboard.

If the wiring in the house doesn't allow IPABXwPP to be installed 'in front' of all tele-equipment, use the following solution:
Place a 12C508 based IPABXwPP with only one relay, in front of each telephone. It can be build for less than $10/each. The phone then rings, depending on which output the relay is connected to.

The SOFTWARE is fairly documented, with both Nassi-Shneidermann diagrams (below), and extensive use of comments in the source (click the subroutines in main and ISR, to view the lower level).
The NS-diagrams were made in a demoversion of Siemens EasyCODE (SPX).

• Wait for ringing.
• Switch off all lines (to suppress the first ring) and turn on led.
• Determine ringing patterns, and switch on selected line(s).
• Wait for ringing to end or wait 30 seconds since first ring.
• Turn on all lines, goto start...

The problem was removed by swithing on all lines in spaces between rings, thereby not allowing the phones on the other line to discharge completely. Sometimes this can give problems with 'tinkling' on phones connected to a line which should not ring, so it's optional (with a 'switch' in the source-file).

The ISR (Interrupt Service Routine) takes care of updating all timers, I/O-operations etc. It's called every 5th millisecond.

The source is not optimized for speed, as it wasn't necessary. It uses about 350 words, and can therefore be implemented in most 16Cxx device. The software were originally written for a 16F84, using a T0 interrupt, but were later rewritten for use on a 12C508 (which hasn't got any interrupt-capabilities). If the circuit is built with a 12C508, change the PROCESSOR-directive, and assemble the file.

History:

Version	Changed	Reason	Date
1.40r	Implemented LED-flashing: Slow/short flash - Idle state Constant on - Incoming call Fast blinking - Phone in use Fast/short flash: Shows which line was called, untill the phone is picked up. Makes it possible to see if the phone rang, but wasn't picked up. 1 short flash shows that diff. line 1 was called, 2 shows that diff. line 2 was called, and 3 shows that the 'normal' line was called.	-	09.07.98
1.35	Changed way of detecting privacy phone. Optimized the source a bit (saved about 20-25 words in codesize).	Problems when using more than 1 IPABXwPP on the same line. -	09.07.98
1.34	Changed "lines switched on in pauses between ringing" to 'optional'.	Suppress relay-noise/tinkling on some (sensitive) phones.	08.07.98
1.33r	Fixed a major bug (software not working at all in a 12C50x). Halted at initialization, until WDT timeout.	Different implementation of FSR between 12C50x and 16Cxx. (Not possible to check for FSR overflow using the zeroflag on a 12C50x).	07.05.98
1.32r	First 'public' release.	-	13.03.98

Read the history at the end of the source-file (main.asm) for description of previous revision.

Download:

Ipabxsrc.zip	32KB	IPABXwPP 1.40 source and hex-file.
Ipabxwpp.zip	210KB	The complete package, including circuit-diagram, PCB-layout, NS-diagrams, source-code and hex-file.
Ipabxepp.zip	59KB	Circuit diagram and PCB-layout EPS format (Encapsulated PostScript).