The Telephone System

The main system unit from BBS Telecom.

System phones have alphanumeric caller ID displays

Purchase and installation

After years of thinking about it, I decided to install a phone system in my home. There were several features I wanted. These included:
The two systems I considered were by BBS and Panasonic. The Panasonic did not have some of the above features, or were available at a large cost. I therefore decided to use the BBS system, and purchased a IPS416 with CID from HAS. The system unit was $900, and system phones cost $180.
In light of the above cost, I considering building my own system. However, there is a lot of hardware needed to implement a cross bar switch for 12 extension, 2 outside lines, 4 intercom conversations, and 2 signal sources (almost 100 switches). I would also need to build the hardware for the signal sources such as the ring and dial tone simulators. All this needs to be committed to PC boards (for reliability). I decided this was just too much work.
In order to prepare for the phone system I home ran Cat 5 cable to the various rooms in my home that didn't have a phone line. I took the opportunity to also run RG-6 into the bedrooms. The installation of the cable was preceded by installing a 2" conduit from the attic to my basement through a hollow chase in my home. I had found this chase while planning the installation of my central vacuum system. Since the ceiling in my basement (which I finished myself) has a drop ceiling, I could already access the hidden areas of the walls on the basement and first floor. After the installation of the conduit, I was thus able to run cable to any room in the house to the wiring closet in a corner of the house. There the phone/Cat5 lines were punched down into 66 type blocks. I then punched the leads of loose RJ11 jacks to the phone lines. These latter jacks allowed me to 'patch' the various extensions into the phone system's extension jacks, and were fastened to the side of the 66 type blocks.
The extensions wired are:
  • Kitchen
  • Guest Room
  • Master Bedroom
  • Master Bath
  • Secondary Bedroom 1
  • Secondary Bedroom 2
  • Secondary Bath
  • Kitchen dining area/family room
  • Den
  • Rec Room
  • Basement Bath
  • Computer
  • Lab/Storage Room
I had previously been envious of people that prewired their homes, thinking that such a desirable infrastructure was beyond my reach. I have since learned that it is just difficult to a varying degree depending on the design of the house. I was fortunate in my case that it really wasn't that difficult to implement, I just needed the realization that it could be done. After having installed a wired security system, a central vacuum system, and this phone system, I have proven to myself that even existing homes can be retrofitted for new technology that comes along.
Use of the system
One of the features of the phone system is the auto attendant. This allows the installer to record a message instructing the caller to press a number depending on the caller's intentions. My message sounds like this:
Only at this point will one of the phones in the house ring. We look forward to fewer telemarketer calls interrupting us. If they still ring our phones, we will just hang up on them, after all, they were warned to leave a message.
My home automation computer is now on its own extension. Since the phone node can seize the line, I have programmed the computer to answer the phone when its extension rings. I can then use the touch tones to send commands to it. This is better than the previous system where the computer starts processing tone commands when I enter a password sequence. This password sequence is intended to be an invalid phone number. This prevents the phone company from connecting me to an unknown location. However, the phone company answers with a beeping sound to alert the caller this number is invalid. The problem occurs when this beeping interferes with my computer's ability to recognize the touch tone command. This no longer occurs since I am having a quiet 'conversation' with my computer on my phone system. I can now also call in from outside and control the home without having to bypass my answering machine or without having to disturb any inhabitants in the home.
A nice feature that I did not expect is how the unit handles fax calls. The auto attendant can recognize an incoming fax call and route it to my fax machine. When the fax machine picks up, and hears the fax tone, it automatically starts receiving faxes. People can now send us faxes without ringing a phone inside the home. They also no longer have to call us first to notify us of an incoming fax.


The Door Phone

Instead of a regular doorbell, one can install a door phone, which allows any person to answer the door by telephone.  BBS used to sell a door phone unit, but at $180 I decided to go with a third party product instead.  The "DoorBell Fon" from LocalPlex is designed to be used with PBX and non-PBX systems, and was installed on the second incoming line.  When a visitor presses the old doorbell button, or the button on the door unit, it causes the phones to ring inside the house, and anyone can pick up the phone to speak with the visitor.
When I purchased the unit, I also wanted anyone inside the home to be able to connect to the door and speak with the visitor even before anyone had pressed the doorbell button.  However, the unit would not perform this action, although this feature was mentioned in an on-line instruction manual for the door phone unit (page 6).  This feature is similar to the "hands-free speaker phone" feature of the BBS key telephones.  Over the years, we have come to like this feature very much.  Thinking it was a problem with my installation, I used the DoorBell Fon in all kinds of configurations, but finally gave up after a few days.  I then called and emailed the manufacturer, and to my surprise, a new version of the microcontroller (it is a PIC) was needed.  Paul from customer support sent a new rev to me at no charge.  I found phone support to be very good, but email support took a week before a response was generated.
I installed the new PIC, and 'bingo' it worked like a champ.  Now anyone inside the home can connect to the door at any time to listen and speak by hitting '62' on a phone.  I can also call from outside the home, and connect to the door phone, answering the door when I am at work or on travel.  Worthington had the lowest price at $98.  A pdf manual is available here from  More technical information on this unit can perhaps be found with a Google Search, or by using the link below.

The Door Phone unit from LocalPlex

Adding a Caller-ID display to the IVT-16

The black "IVT" system phone that is available from BBS comes in two flavors.  The IVT-16D has an LCD display that displays Caller-ID information (if the phone system has that option), and the IVT-16 (a.k.a. IVT-16N), which has no LCD display.  I purchased one unit of the latter type from a person on ebay, and decided to open the unit up to see if a display could be added.

LCD display on the IVT-16D. Apart from basic system status, it also displays
the Caller-ID information of the caller.

The IVT-16, which has no display. The location of the display has a black plastic plate.
When this phone is powered up, the 'MEM' LED (top middle) lights up as a power indicator.

Internal look of the IVT-16D.  The LCD display is in the right half, on the top.

Once I compared the two units' innards, I realized that their electronics were identical (as I had hoped), except that the IVT-16 was simply missing an LCD display!  Even the connector where it would be plugged into was intact.

Inside view of the IVT-16, note the missing display although its
connector (orange) is present.  The spacing of the pins on
the connector is 2mm (0.075"), and there are 14 pins on it.

When the IVT-16 is powered up, its 'MEM' LED lights up, perhaps as a power indicator (since there is no display).  When I unplugged the LCD panel from the IVT-16D, its 'MEM' LED lit up too!  This implies that the firmware on both phones is similar, except the microprocessor detects the missing LCD, and lights the 'MEM' LED up.  I then plugged in the LCD panel from the IVT-16D phone into the IVT-16, and the display showed text!  This confirms that the firmware is functionally the same on both phones.

A closer look at the LCD panel on the IVT-16D shows that it has a '44780' microprocessor.  I was really happy to see that as many LCD panels that are available on the surplus market use this controller.  I thought to myself, perhaps I could simply purchase an LCD panel and upgrade my IVT-16?  A look at my favorite surplus place ( showed that they had a 20x2 display (model LCD-95) with approximately the correct overall size.  It's price was $6.50.

I purchased two LCD displays (one spare), and found a 2mm connector to mate into the phone board.  I then connected the display to the orange connector on the phone board (pin 1 to pin 1, etc).  When I plugged the phone into the phone system.  Success!  The display lit up.  Amazingly, the mounting holes in the panel lined up with the screw holes in the phone case.  I then attached the display into the phone with some screws and covered the opening with a clear sheet of plexiglas.

The new display inside the IVT-16.  I used a 30 pin
connector to hold the 14 wires so that
it could be plugged into the back of the LCD display.

The finished installation of the display.  The whole opening is
covered with a clear plastic sheet cut to the correct dimensions. 
It is nearly impossible to see the clear plastic in this picture.

Incidentally, I also purchased a 24x2 LCD display from All Electronics (model LCD-74), and since it already had a 2 mm connector on it, I plugged it into the phone, and that worked also.  However, the extra width prevented a good way of mounting the display into the phone.  I presume the extra eight characters on the display would remain blank.  This compatibility does not surprise me as the 44780 controller is addressed the same way regardless of the size of the display.

So to summarize, the overall upgrade project cost is about $7.00 (with shipping, etc), and one 2 mm connector from my junk pile.  On the Lee Phones website, the IVT-16 costs $135, while the IVT-16D costs $165, so I saved myself a little bit of money.  As we can see, it is easily performed using commonly available components.

Changing the internal lithium battery
The configuration of the system, and the system time (but not the outgoing auto-attendant message) is stored on a M48T08-150 Lithium battery backed RAM.  At around 2012, the system no longer preserved its configuration after power cycles, and it was clear that the battery was depleted after 15 years of operation.  Not bad really.  I decided to install an external battery holder to solve this problem completely.

After I opened the system and found the RAM module (it is socketed and on the main board), I did a web search and found this article from someone that actually ground open the module to install an external battery. 

M48T08 opened
Photo of the RAM module ground open to expose the small Lithium battery.
Note that the side opposite from the case's pin 1 is ground open.

The above photo shows the RAM module ground open with my bench top grinder.  The bottom case of the battery is the '+' terminal, and it is welded to the contact circled in red.  While the top terminal was connected to the one circled in blue (but interrupted here).  I found that once I ground through the case, the potting material (slightly grey) was softer, and I could pick it away with a sharp screwdriver.

With battery connection
RAM module with external battery.

I wired a long pair of wires to the terminals and attached to CR2032 batteries.  Instead of storing the new batteries inside the case (which would give a cleaner look), I decided to have the batteries be external so that I would not have to disconnect the phone wires the next time.

Tips and Tricks

There is a serial port on the system unit that connects to a PC for programming. In my case, the PC is far from the system unit, so I needed to run some kind of cable. It turns out that only three of the nine pins on the DB9 are used (2,3, and 5), so I plugged in a DB9-RJ11 adapter. This allowed me to use a regular phone line to connect the system unit to the PC. This arrangement actually looks very good since the whole interface to the system unit is power and RJ11 plugs.

Project Log

Second bbs unit
Label on the back of the second unit from ebay.  The "CID" on the label
(and a label on the CPU) confirms it has the Caller-ID option.
If the unit does not have Caller-ID, the CID will be "MVX" (example)
  • November 2003 - Purchased two IVT-16D alpha-numeric keyphones for about $42 each on ebay (these phones normally auction for at least $75).  Lee phones, who has the best on-line price for these phones sells them for about $165 each. 
  • February 2004 - Purchased an IVT-16N phone (no LCD display) on ebay for $36 (+ shipping), and added a display (see above). So currently I have 6 key phones with alpha-numeric display, and 2 without.  Specifications on the display:
    • Optrex #DMC-50218.
    • Viewing area, 3.26" x 0.7".
    • Module size, 4.58" x 1.46".
    • 5 x 8 dot characters.
    • Prepped with 7 x 2 dual-row header, 0.1" spacing.
    • CAT# LCD-95. Price: $6.50 each
  • October 14, 2004 - Purchased an IVT-16N (no LCD display) on ebay for $28 (+9 shipping).  Display added as above.
  • October 15, 2004 - Purchased an IVT-16D on ebay for $0.01 (+$12 shipping).  What a great buy.
  • October 23, 2004 - Purchased an IVT-16D on ebay for $1.57 (+$14 shipping).  Now I have plenty of spares.
  • December 5, 2006 - Purchased two IVT-16D on ebay for $41 (+$9).
  • November 13, 2007 - Problem with door phone unit.  It stopped working.  When I connect to the door unit from an internal phone, I get a fast busy signal.  After an investigation, I find that the problem is a simple wire break to the door unit.  Thus the main box reacts by sounding a fast busy in this case.  I recall that when I purchased the unit, they sent me a custom chip that makes it compatible with phone systems.  The fast busy does not occur with the original controller chip.  The manufacturer is still around, and I contacted them to purchase a spare controller chip (Model #N8-NC) for $10.
  • September 1, 2014 - Added external lithium battery for the battery backed RAM.
  • Spring 2015 - After 18 years of service, BBS unit #1 experienced a failure.  When a non-system phone is called, the system performs a reset.  It appears that sending the high voltage ring signal causes the reset of the system.  This reset is similar to a power cycle.  I replaced it with a spare unit (#2).  #1 will be repaired in the future.
  • September 2016 - Replacement of Door Fon parts.  I had picked up spares for low cost on Ebay over the years, and these came in handy.  The outside unit button, mike and speaker had degraded (seamingly all together) so those were replaced.  Also, the inside controller did not consistently detect that someone wanted to connect to the door (from inside the house).  This original set was in use almost twenty years.
  • March 2020 - Received email from Paul  regarding the repair of his unit. 
Hi Ed,

I've repaired my IPS416-CID. I put an oscilloscope on the power supply's 5V output and saw a lot of ripple, even when not ringing. Rather than troubleshoot further, I simply replaced all seven of the power supply section's electrolytic capacitors (C25-C31) and that fixed it.

These are very versatile phone systems! I've never found anything else with quite the same functionality at a similar price point or footprint, so I also have a spare unit. This isn't the first repair I've done on them. If you get your phone service from a traditional landline provider and have ever lost a trunk port to a surge, the part that usually fails is its LCA110 6-pin DIP solid-state relay on the daughter-board. When I've replaced them I added a 6-pin DIP socket to make future replacement easier.


This result above is one that I should have foreseen.  Problems during high draw events that lead to reset strongly suggest a power supply issue.  So kudos to Paul for thinking of this.  I opened up my 'bad' unit to get some additional info, and found that the unit has a positive voltage supply and a fairly high voltage negative supply.  The latter is probably for the 'ring' power.  Anyone repairing these supplies should check the ripple of these during high current draw events or just replace the power capacitors as Paul suggests.

probe points
Corner of BBS unit with power supply. Meter reference is D3 in black box
(under the big white resistor), 5V is C19 in the red box (<10mVrms ripple),
+11V raw supply is yellow box (~0.26Vrms ripple),
-43V raw supply is pink box (~70mVrms ripple).
These ripple numbers for a good unit.

  • July 2022 - I performed a repair on the failed unit from 2015 (BBS #1).  The ripple on the six capacitors in the bottom-right of the above image were all about 60mVrms except for C27.  This 1000uF capacitor measured 800uF and had 0.8Vrms of ripple.  I replaced this unit and the ripple was reduced to 0.2Vrms.  Ripple on the 5V portion is less than 10mVrms.  The unit no longer resets when a non-key phone is called.  I also used this opportunity to delid and attach a remote battery holder to the RAM.  The battery holder was from a toy LED bracelet and uses a CR2032 battery (shown below).
Clock/RAM chip external supply.

main power supply sketch
Sketch of main power supply.  Dx are the bridges.
  • 2023 - I did some research on backup power for the key phones.  It is a bit annoying to walk all over the house to enable "Auto-Answer" when power is cycled on the system unit.  The phones are powered by about 30-34Vdc on the outer pair of wires on the modular phone cable (yellow-black pair).  A voltage as low as 5V will keep the settings on the phones.  It turns out that the 16 phones are powered in four banks.  Each bank has transistor switches to enable/disable their supply.  So a simple standby supply is not possible.  Current for each phone is as folows, at 12V, the phones draw 40mA each.  At 6V, the display dims and the draw is 32mA.  At 5V (24mA), the display is blank.  Finally, at 4V, the phone shuts down.
power supply for phones
Simple sketch of phone power.  Four extensions are
powered by these two transistors.
  • Sept 2023 - One of the system phones (master bath) malfunctioning by sporadically beeping loudly like a busy line was called.  Set it up near my test bench to replicate the issue.  Then a few weeks later the system (Unit #2) stopped working.  Checking the ripple on the power supply caps showed the +11V had 2.6Vrms of ripple.  Replacing C27 reduced this down to 0.261Vrms (similar to Unit #1 after its repair).  The old capacitor measured 725uF.  This capacitor looks like the weakest part of the original system.


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