weeBell - personal central office for POTS phones

weeBell brings the goodness of old telephones into the modern age in a portable package that speaks GUI, Bluetooth and Wifi

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weeBell is a platform designed to make it easy to (re)use old "POTS" telephones - rotary or DTMF. It is comprised of two boards I designed - gCore and the gCore POTS shield. gCore is a high-end ESP32 development board aimed at making portable gadgets with graphical displays. The gCore POTS shield contains the circuitry necessary to implement a local area "line card" providing the proper signaling for traditional 2-wire telephones. You can plug a telephone directly into it or you can connect it to the existing wiring that might exist in your home or business and then plug one or more telephones into other jacks around the home or business.

Different software running on weeBell can do things like let phones call using a cellphone or implement a SIP-based VOIP phone.


In 2019 I made a gadget called Blue POT that let us use an old 1945 rotary telephone we had with our cellphones.

It was fun but suffered from some issues.  Audio levels weren't great, there was noise and configuring the BM64 bluetooth module was a huge pain.  I always wanted to revisit this project because I find old telephones and their history to be very fun and interesting.  Finally this year with the completion of my own development board I decided to revisit my old telephone project.  However this time I decided to make a more general purpose gadget - weeBell.

The name weeBell is a play on both small and wireless and pays homage to the granddaddy of all technology companies, AT&T or simply "Ma Bell".  In 1984 AT&T's telephone system was split into several regional telephone companies or Baby Bells as they were christened.  weeBell is an even smaller regional telephone provider...a provider for one.

(back when talking on the phone was glamorous)

Start of the project

The ESP32 is a tremendously capable chip.  With two processors it can take on a lot of real-time processing tasks and the Espressif IDF provides support for classic Bluetooth handsfree profile as well as SIP telephony.  I'm sure Espressif intends this stuff to be used in little "Alexa" like speaker gadgets but I figured it could also be used with the SLIC module I originally used to talk to POTS phones.   This meant I could make a device that could be used for a variety of end uses.

  1. Using POTS telephone to place and answer calls through a cellphone
  2. Implementing a VOIP phone using the SIP protocol to talk to asterisk or other SIP providers
  3. Creating a Museum or Art installation controller that lets people interact with (and perhaps store) messages stored on a Micro-SD card from a phone.   Different messages could be reached by dialing different numbers.  Or maybe messages could be left for others to discover (lol, maybe this wouldn't be a good idea for the general public...)

I started with the bluetooth implementation.  It took me weeks of effort to understand how I could reproduce my original gadget because I had to learn about the Espressif Classic Bluetooth library (with detours to Bluekitchen's BTstack and Espressif's ADF and back), and figure out how to deal with things like echo cancellation (thankfully I could stand on the shoulders of some real experts, like Dave Rowe and Steve Underwood, who shared their telephony code). 

gCore's first shield

Finally I had a rough prototype running and could design a new PCB to hold the telephony components.

I started with the NXP SGTL5000 Codec chip, mainly because I had one laying around on a PJRC Audio shield.  The hybrid function is once again provided by the Silvertel AG1171 SLIC module.  It adapts the audio to and from the codec to the telephone line, generates ringing voltages and can detect hook actions (used to determine off-hook condition and rotary dialing).  I briefly thought about trying to design my own analog circuitry because the AG1171 had gotten a lot more expensive but quickly realized best to leave this to the professionals.  There is some additional protection circuitry since the AG1171 is specified to drive up to 1 km of wiring.  But that wiring is meant to be "on-premise", meaning within one building.  It can handle typical induced spike voltages but can't handle a lightening strike like telephone company line cards could.  What is neat about this is that you can connect weeBell to the existing wiring in a building (disconnecting it outside the building!!!) and then plug up to three POTS phones into other outlets on the same circuit.

Here's the output circuitry on the initial revision of the PCB.

The bridge rectifier and ESD suppressor shunt excess voltages to ground.  The resistors allow the AG1171...

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gCore POTS Shield Schematic (Rev 3)

Adobe Portable Document Format - 66.24 kB - 07/03/2023 at 19:48


  • weeBell Bluetooth firmware version 1.0 - with Caller ID!

    Dan Julio6 days ago 0 comments

    I have finally fulfilled a goal I had since my original BluePOT project back in 2019 - to add Caller ID support.  I know that it's not used by very old phones but I always felt it had to be there for me to claim my gadget was a good replica of a real phone system.  Plus I wanted to learn how it was done.

    Took longer than I thought it would

    Actually, thanks to spandsp, adding Caller ID support itself wasn't that hard.  A new state machine in pots_task and some new audio paths.  I also had to add support for date and time as Caller ID sends this along with the phone number so I added a new GUI screen to set the time and some timekeeping utilities.  Unfortunately it uncovered some confounding bugs as I would return to my desk in the morning to find the weeBell clock was massively slow.  Turned out there were two bugs.  One of which I fixed and one I am currently working around.  The gCore RTC is used in a traditional HW RTC mode.  It sets the time when weeBell boots.  The system clock maintained by FreeRTOS is used as the operational time while weeBell runs.  I found that both would be slow after a night where my cellphone was across the house and the Bluetooth connection between weeBell and the phone was very "iffy".  At first I was confused why both would be slow but by different amounts.  One of those situations where something confusing makes it hard to look in the right place to identify a problem.  But after a bit I realized they were unconnected.  Turns out the gCore RTC bug was because heavy I2C activity could cause it to miss once/second RTC interrupts.  While weeBell runs it is constantly polling the gCore RTC/PMIC EFM8 micro-controller to see if the user has pressed the power button to turn the device off, as well as looking at battery and charge state for the GUI (and low battery shutdown).  All of that polling was slowing down gCore's RTC.  With some restructuring of the EFM8 code I was able to fix that bug (described here).  However the system clock slowdown is still not entirely understood but I am pretty sure it has to do with the Espressif Bluetooth stack perhaps blocking timekeeping interrupts in the ESP32 under conditions where it is working excessively hard to initiate or maintain a Bluetooth connection. I am still debugging this (it is a slow process) but put in a work-around that seems to be ok.  Every hour the gcore_task checks the HW RTC time against the system time and adjusts the system time if it finds the system time has drifted.

    I also tuned up overall operation a little (the backlight fade-up and fade-down are much smoother now) and added a few countries (discussed below).  All-in-all I'm really happy with this release.

    Audio Architecture

    The primary addition to the audio subsystem is a FSK Modulator capable of either Bell 202 or V23 frequencies.  This is essentially a 1200 baud modem implemented in software that is one way Caller ID is transmitted to the phone.  The other way Caller ID is transmitted is using DTMF tones.  The block diagram below shows the new audio architecture.  In fact I have two DTMF encoders.  The original is still used to generate DTMF during a phone call (for example a user of a rotary phone can type DTMF codes for '#" and '*" on the GUI to access a phone tree).  The spandsp library also includes another DTMF generator in the Caller ID support functions.

    GUI Changes

    GUI changes were easy.  Another control on the Settings screen takes you to a Set Time/Data screen.  I copied most of the logic for the Set Time/Date screen from my own tCam firmware.  I also copied over RTC and time support utilities from that project and modified them slightly for weeBell.

    The time and date are also displayed on the main screen while it is connected to a cellphone.

    The quick&dirty about...

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  • The wide world of telephony

    Dan Julio08/20/2023 at 19:47 0 comments

    I am currently adding support for Caller ID and hopefully some more countries.  This process has involved a humungous amount of online searches and, now fortunately, discovery of a few online groups of real telephone aficionados such as the Classic Rotary Phones forum, Telephone Collectors International and their forum and others.  The problem is that a lot of information about telephone systems from around the world doesn't seem to have been documented in a searchable way online.

    But this log entry isn't about my troubles.  It's to share some fun things I found along the way.

    AT&T had to teach Americans how to use a Dial Telephone

    The first dial telephones were manufactured in 1897 but Bell didn't start rolling them out until 1919.  Unbelievably, it took until 1978 for the entire United States to receive dialing capability!

    Here's a short video of a newsreel shown in movie theaters the week before a town or region would be switched over to dialing.

    And a longer video about a fictional town being taught how to dial (skip to 5:30 to get going or start at the beginning to realize how much shorter our attention spans have become).

    Odd Rotary Dials

    Most of the world used the same rotary dial layout that starts with the digit "1" (generating 1 pulse) and ends with the digit "0" (generating 10 pulses). 

    New Zealand used that standard format but also had  a reversed format starting with the digit "9" (generating 1 pulse) and ending with the digit "0" (generating 10 pulses).

    (courtesy Nition1 under the Creative Commons license)

    And in Sweden the phones started with the digit "0" (generating 1 pulse) and ended with the digit "9" (generating 10 pulses).  The engineers who were implementing the first Swedish telephone network must have thought the rest of the world crazy with their out-of-sequence dials.

    (courtesy Holger.Eligaard under the Creative Commons license)

    weeBell handles these different dial layouts using a mapping structure that is part of the international.c file entry for each country.  For New Zealand I will have two entries "New Zealand" and "New Zealand Reverse". 

    The first DTMF phones

    Here in the USA the announcement of Touch Tone dialing was made at the Seattle World's fair in 1962.  A new Western Electric 1500-series phone was introduced and became available in 1963 (source).  The interesting thing is that it only had ten buttons.  The * and # keys we all know today weren't added until 1968 with the 2500 series.

    Paul-F's website has a very interesting discussion of Touch Tone development.  There was a lot of what we now call User Experience (UX) testing before Bell Laboratories settled on the ubiquitous keypad layout that still appears on our cell phones today. 

    (Source: Bell System Technical Journal, July 1960, p. 999
    "Human Factors Engineering Studies of the Design and Use of
    Pushbutton Telephone Sets," by R. L. DEININGER)

    As most of us know, the DTMF tones are comprised of two frequencies (row and column).  weeBell generates them in software using a DDS synthesizer (essentially a sine wave table lookup, scaling and mixer).  Lots of transistors involved in that (but they're cheap).  I couldn't find a schematic for the 1500 series but the 2500 series keypad uses a single transistor along with a tapped coil to generate both frequencies.  A less known fact about DTMF tone generation is that an additional four keys are specified - 'A' - 'D' - which were typically used for network control although they made an appearance on some military phones and are still used by Amateur Radio operators for remote system control today.

    A Morse Code Dial Tone?

    You bet.  Up until 1979 the German telephone system used pair of 475 Hz tones, the first 200 mSec long, and the second 700 mSec long separated by 300 and 800 mSec gaps.  This is morse code for the letter 'A'.  You can hear it here.  After 1979 they...

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  • Audio Architecture

    Dan Julio07/31/2023 at 18:13 0 comments

    The most interesting part, for me, of the Bluetooth Handsfree firmware for weeBell has been the audio subsystem.  I've never really done real time audio before (aside from generating tones or using a library with a I2S DAC) so it was a good learning experience.   Aside from the hard real-time nature of audio, there were several technical challenges to overcome.

    Perhaps the most difficult technical challenge was Line Echo Cancellation.  All POTS telephone interfaces multiplex received and transmitted audio onto the same two wires going to the telephone.  Traditionally this was done by a circuit called a Hybrid which consisted of a set of coils or transformers.  For weeBell, it's done by the AG1171 with active circuitry.  One of the characteristics of the hybrid is that it echos back received audio due to impedance mismatches.  In a system that has hundreds of milliseconds of delay, such as a long distance line or a cellular connection, this causes the remote talker to hear their voice echoed back to them and is unpleasant.  The introduction of long distance calling required the telephone companies to find ways to cancel that echo through Line Echo Cancellation (or Echo Suppression in the early days) where the received signal is subtracted from the echoed signal in the transmit path before being sent back into the network.  Here's a paper that discusses the echo canceller Bell Labs developed when sending telephone calls through the Telstar satellite.

    (picture from David Rowe's blog)

    I was initially concerned about how I would perform this function but fortunately we live in the glorious time of searches and code repositories.  This problem - and others - has been solved many times and I found David Rowe's amazing OSLEC (Open Source Line Echo Cancellation) code along with a bunch of telephony functions in Steve Underwood's wonderful spandsp library which was archived from SVN to github.  Originally written for Asterisk this C code is incredibly well written and easy to use.

    My code includes the ability to store the audio samples surrounding the OSLEC routine to gCore's Micro-SD card and I used that a lot while developing the code.  The following image shows OSLEC in action with the samples displayed in Audacity.  The TX audio path is from the remote speaker intended to be heard in the handset.  The RX audio path shows the echoed signal from the hybrid before echo cancellation.  And the EC audio path shows the signal from the hybrid after echo cancellation as it is returned to the remote talker.  You can see OSLEC has a very short "training" period and then is very effective in removing the signal.  There's lots more to it and you can read about OSLEC's development on David's blog starting with this entry.

    The spandsp library also provides DDS tone synthesis (including DTMF tone generation) and a goertzel based DTMF tone decoder that I press into service as well.  In the future I want to use the modem functionality in the library to generate caller ID information.

    The overall audio architecture is shown below.

    The real-time audio subsystem is contained in the audio_task that has CPU 1 all to itself.  It runs with a 8 kHz sampling rate since that's what spandsp was designed around.  In addition to the functionality provided by spandsp the audio subsystem also has to convert the 16 kHz sampling rate the Bluetooth Handsfree audio connection can use if both the cellphone and remote device support the MSBC codec. 

    Both downsampling from 16kHz to 8 kHz and upsampling from 8 kHz to 16 kHz are slightly more complicated that just halving or doubling the data because of the frequency aliasing and non-linear distortion.

    Downsampling is very simple and compute efficient.  Each two samples are averaged as a simple low pass filter and generate an output rate of half.

    Upsampling is slightly more complex and uses...

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  • Testing with the mother-load of POTS phones

    Dan Julio07/09/2023 at 17:55 0 comments

    I spent a recent morning at the home of my friend (and great electrician) Randy P who is a telephone collector.  It wasn't until years after we met I learned of his hobby and he was someone I had in mind as I designed weeBell.   He graciously offered his collection and time to test weeBell_bluetooth with a bunch of different phones.

    We setup on his kitchen table and both placed and received calls with different rotary dial and DTMF phones.

    We had a huge inventory to choose from:

    And I'm not even showing the Star Trek phones...

    Sadly I didn't think to bring some extra wiring supplies so phones that used the very old 4-prong connector couldn't be tested.  Another day for that I hope.

    Testing went well including the discovery of a firmware bug.  One of the rotary phones dialed incorrectly (dialing a 2 returned 1, dialing 1 returned no number at all).  But this only malfunctioned after the phone had rung for an incoming call.  I brought the phone back home with me and connected the GPIO signals to/from the AG1171 to my scope.  The problem was immediately obvious.  There is a signal to the AG1171 called RM which is driven high when you want to initiate ringing (another signal, F/R, toggles to actually ring the bell).  My code was leaving RM high as shown in following image taken from the AG1171 datasheet.

    For some reason, that I didn't puzzle through, the phone does not register the first switch closure as the rotary dial moves after dialing.  The bug was a slightly embarrassing one line fix.  I have a subroutine which is supposed to be called at the end of a ring.  It both sets the state of the software ring state machine and the correct GPIO outputs for RM and F/R.  However my code was simply setting the state instead of calling the routine.  Changing the direct setting of the state variable to a subroutine call fixed the problem.

    Looking at Randy's collection was a lot of fun.  A couple of phones were really interesting as they show the features we use today were explored a long time ago.

    Multi-line phones first made an appearance in the 1930s.

    And the video phone in the 1960s.

    Sure would be fun to try to make that work again but Randy looked slightly askew at me when I suggested it... :-)

    I'm giving Randy a weeBell and he said he plans to use it in his truck and on job sites with different old phones.  He's sure it'll turn a lot of heads.

  • Boards up on tindie

    Dan Julio07/03/2023 at 18:34 0 comments

    Tindie approved the store entry for the ten boards I built.  I also put together a kit with a gCorewith header pre-soldered (and weeBell_bluetooth preloaded) and mounting hardware.

    You'll need a 18650 LiPo battery to fit in the 3D printed enclosure as well.  Adafruit has an battery with the correct JST cable already connected (you can also buy it from Digi-Key).  Or you could make your own by soldering or spot welding a JST cable assembly to an existing cell (I know people don't like to solder to battery terminals but I've never had a problem).  Just make sure the 2-pin JST PH connector has the Sparkfun/Adafruit polarity.

  • Rev 3 board qualified and a few built

    Dan Julio07/01/2023 at 17:32 0 comments

    The integrated I2C filter on the Rev 3 boards works and I built up a small set of boards to try to sell on tindie to see if people would be interested in buying weeBell kits.

    Old bug found and fixed

    Some of my original Teensy code that handled the AG1171 ringing control made its way into the ESP32 code-base.  I used two phones to test the Rev 3 boards I had built to make sure all functions worked.

    During testing I noticed that the rotary phone bell would ring but the more modern DECT wireless phone would not.  This made me worry that I had a hardware issue of some kind (not a great feeling after hand building 10 boards).  Connecting the scope to the tip and ring signals showed reasonable voltages during ringing (not what central offices used to generate but close to what the AG1171 spec claimed it would generate).  I was puzzled, until I told the scope to do a set of measurements to get the RMS voltage and it also told me the frequency was 10 Hz.  Oh snap.  I hadn't even noticed the timescale.  My code was generating a ringing frequency half of what it should have been (USA has 20 Hz ringing frequency).  Simple code fix.  But what was funny is that in all the years playing with this stuff (from Teensy days through weeBell) I had never recognized that when the phone rang it was way too slow of a ring.  But instantly my brain recognized the fixed ring as the way it should sound. 

    Also slight GUI mods

    I made a small change to the background of the slider and slide-switch widgets so they show up better on the settings page.

    Version 0.2 firmware will be pushed shortly.

  • Initial projects pushed to github

    Dan Julio06/27/2023 at 21:34 0 comments

    My vision is that the weeBell system can have several different applications, each with different firmware.  So to this end I am creating repos for each of the applications and another for hardware documentation.

    1. Hardware documentation can be found at weeBell_hardware
    2. The bluetooth application for weeBell can be found at weeBell_bluetooth

    All code is GPLv3. 

    I've also built up about 10 gCore POTS shield boards and as soon as I test them I'll add them for sale on my tindie storefront.

    Still trying to coordinate with my friend who has a huge telephone collection to test with.   I suspect there are still some issues with audio processing.

  • Third time's the charm (he says hopefully)

    Dan Julio05/29/2023 at 15:16 0 comments

    Oh difficult child, you

    I received the Rev 2 boards and ES8388 codec chips last week and got a board built up.  It took a day more to finish the codec driver port and then I could start debugging.  After working through the initial compile errors, I was immediately greeted by I2C errors communicating with the ES8388.  Lots of them.  Sometimes the chip simply wouldn't respond and other times it would respond to an address but not let go of SDA at the end of a cycle leading to a timeout.  At least it wasn't f*cking up transactions to the other chips like the SGTL5000 did but I was seriously bummed.

    Scope traces looked fine but clearly something was wrong.  Things got slightly better when I removed the second set of pull-ups on the board (leaving only gCore's 10k pull-ups).  I could at least get through the codec initialization sometimes.  Then I would see failures when I2S was running (2.048 MHz MCLK) and the chip was accessed to change volume (but no errors when I2S wasn't running).  I could see some apparently slight indications of cross-talk, but at least on my 200 MHz BW scope, they didn't appear to violate the VIH and VIL levels in the ES8388 spec sheet.  Perhaps, though, the ES8388 was seeing  some ultra-fast glitches as additional clock pulses.

    Should have followed through with more research

    Then I remembered seeing something on the schematic for the AI-Thinker A1S ESP32 module which has the ES8388 built-in (I used their dev board to play around with the HF demos originally). 

    There is what looks like an RC filter on the I2C signals going to the ES8388.  I originally dismissed this circuit when I laid out my board thinking the designers must have been over cautious but in the light of my own failures I had the realization that circuit was probably there for a reason.  Doh'

    Some quick digging turned up Espressif's Lyra T dev board schematic complete with a note...

    Oh crap.  I shouldn't have been so quick to dismiss what I'd seen.

    A quick hack later and my board had a similar filter on the I2C lines.

    Look at the top left corner of the image.  You can see 2 15k pull-ups tombstone style and 100 ohm resistors soldered to the cut traces.  22 pF caps are where R1 and R2 used to go completing the filter. 

    It worked.  I2C errors were now a thing of the past.  So a note to anyone thinking of using the ES8388 ... remember to include a filter!

    I could now finish debugging the ES8388 driver which mostly meant adjusting various gains so the audio sounded right although I included a bit of black magic I found in the Espressif ADF driver that accesses undocumented registers with the comment that it's to make 8 kHz sampling work (which is what I use).

    One more round of boards

    Let's hope the third time's the charm.  At least the modified Rev 2 board seems fully functional and I am planning to take my proto to visit a friend who collects antique phones for an afternoon of calls making sure this works with a variety of phones.

    R1-R4, C1, C2 are the I2C pull-ups and filter.  Rev 3 also got some more warnings and notes.

  • Bluetooth tamed (with a compromise and a surprise)

    Dan Julio05/27/2023 at 19:38 0 comments

    Lots of code changes later, I'm finally happy with the state of things - at least on iPhone - I have yet to test with an Android phone.  The device is able to reliably reconnect when a phone comes back in range and other functionality seems stable.  And it seems to handle all the possible situations with audio routing and various bluetooth low-level notification traffic.

    Fast Support from Espressif

    I found a bug in the Espressif low-level (binary blob) Bluetooth library that would crash the app (StoreProhibited) if the phone was at the edge of Bluetooth range.  At night I sleep with the phone on a nightstand across the house from my lab.  I leave weeBell running and logging output and in the morning I noticed it would crash and reboot many times overnight.  Sometimes with a cryptic error from the low level code.  I dove into the Bluedroid library port but was soon stymied by the lack of source for this library so I posted a bug report on Espressif's IDF repo late one night.  Much to my surprise there was a response the next morning from an engineer saying to try a version of the library they had published two months prior (I thought I was up-to-date but I wasn't).  Boom!  That fixed it.  The engineer then checked back with me a couple of days later to see how I was doing.  I was really impressed. 

    A compromise in security

    I hope to be able to use the modern Bluetooth Secure Simple Pairing (SSP) mechanism to pair weeBell with a phone.  Although in reality this gadget probably doesn't need to be incredibly concerned with security I wanted experience  with this part of the specification and the Espressif implementation supports it. 

    The old PIN method of pairing devices is insecure.  It can be snooped and has the potential for a man-in-the-middle attack.  SSP uses cryptographic means to protect both sides and has several mechanisms for user confirmation as well.  My implementation displays a 6-digit code on the GUI in a pop-up dialog box and the same 6-digit code should be displayed on the cellphone during pairing.  The user confirms both match and the pairing is completed.

    Only the iPhone displays a dialog box asking if you want to share your address book instead of the 6-digit code.  So the pairing can't be confirmed back to weeBell (although the iPhone thinks it has successfully paired!).

    What is interesting is that the pairing process creates a bonding record in the ESP32 NV storage (where it stores remote devices MAC addresses, keys and the like) even though my code never got the callback indicating authentication had been successful.  Before I updated to the new low-level library I would get a callback indicating the iPhone wished to pair around a minute later and both my code and the iPhone would display the dialog boxes with the code and they could complete the pairing.  However after I updated the low-level library this no longer occurred so there was no way to pair with my iPhone.

    Long story short, I ended up - at least for now - falling back to the older PIN style of pairing and that works.  At least I don't use the pins 0000 or 1234 - and my device only advertises itself for discovery during the 30 second max pairing window when the user presses Pair.  

    Hopefully over time this can be figured out.

    The current ESP32 Bluedroid implementation does not support the PBA or PBAP (phone book) profiles.  These are what your car uses, for example, to display the name of who is calling and to let you access your phone's address book from the car's touchscreen.  I submitted a feature request so hopefully Espressif will support this someday and then I'll add support for it in the GUI.  But it's still strange the iPhone displayed this message when the device it's connecting too doesn't support it.  I wonder if either Apple simply assumes any HFP device will support...

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  • 3D printed enclosure

    Dan Julio05/18/2023 at 20:03 0 comments

    I took the gCore demo enclosure and expanded it to hold an 18650 battery and the gCore POTS shield.  My partner took one look at my freshly printed prototype - that I was proud of - and sniffed "it sure is boxy".  I guess that's the outcome of only knowing OpenSCAD as a 3D design program.  The loved-one-of-my-life's opinion not withstanding, I'll put the design and STL files in the repo when I create it in case anyone is interested.  Maybe someone else will create some awesome 3D printed design.

    It can be assembled with some M3 x 0.5 screws and standoffs (better instructions will be in the repo).

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david lee wrote 06/28/2023 at 12:44 point

Currently I have an old Panasonic pbx system (KX-TA624) in the house with 6 rotary phones in various rooms as a "intercom" system (ie, internal extensions, no ext line out). Wondering if you plan to allow ganging together of your shield to accommodate more than 3 extensions? Also, if you want to incorporate some of the standard panasonic pbx functionality, i'm happy to provide whatever info I might have about the system as you develop things. I would love it if I could connect my cell via bluetooth to your shield and dial POTS extensions from my cell! That would be a cool extension...

  Are you sure? yes | no

Dan Julio wrote 06/28/2023 at 14:40 point

Hey David, your system sounds fun.  The shield itself could be used with other controllers (and other software).  The codec chip on it is an I2C device with one of two possible addresses so it'd be easy to connect two of these to a micro (you'd need 2 I2S interfaces as well).  Beyond that you'd have to do more work (I2C bridges or multiple I2C busses, multiple I2S interfaces).

I don't know anything about the TA624 but I imagine it has at least one port designed to connect to a central office.  You could connect this to weeBell and then configure your PBX so that it did something like ring one or more of the phones when you got an incoming call and connect your POTS phones to it when they dialed "9" for an outside line.

  Are you sure? yes | no

JR wrote 05/18/2023 at 15:43 point

I'm hoping to find a simple solution to VOIP not having affordable loud bells or bright light to indicate phone calls, in a noisy shop environment. 

  Are you sure? yes | no

Dan Julio wrote 05/18/2023 at 20:16 point

weeBell isn't a VOIP phone yet (I hope to support SIP based telephony one day).  But I know there are plenty of existing commercial VOIP adapters out there (ooma for example).  If I understand your desires correctly perhaps you could find an existing commercial device that sits on a POTS phone line and flashes a light or rings a very loud bell.  In fact, many years ago I bought my father one of these buzzers so he could hear his phone ring when he couldn't bother to put in his hearing aids.  It just plugged into a phone jack.

  Are you sure? yes | no

Justin Hunt wrote 05/18/2023 at 13:20 point

I'd just like to basically connect phones around the house as an intercom system using ethernet or standard telephone line cabling. 

  Are you sure? yes | no

Dan Julio wrote 05/18/2023 at 20:12 point

I think the complexity of your project depends on what kind of dialing/ringing/etc you want, and how many phones.  Although I haven't started on the code yet for it, eventually I'd like to implement a SIP based interface (via wifi) to something like a local asterisk server.  That would let you implement an intercom but it would be fairly pricey.  Depending on your skill level it might be less expensive to build your own tiny PBX using the AG1171 modules to handle the line interface and ringing, some sort of local Arduino-like micro to handle the logic (dial decoding, ring generation, audio routing) and a small NxN array of analog switches to route the audio between phones where N is the number of phones the system supports.  Perhaps google would show someone else has already done something like this (I wouldn't be surprised).

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Justin Hunt wrote 05/19/2023 at 01:11 point

Thanks Dan. I am pretty much way at the low end of the skill spectrum. It would be enough to just have two phones, and one ring when the handset on the other is lifted. But I will keep an eye on this project. Good work, it looks great

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scott wrote 05/18/2023 at 12:48 point

I'm very interested in testing and contributing to this project in the area of analog modem communications..  slow modems to be more precise..  

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Dan Julio wrote 05/18/2023 at 20:06 point

Can you elaborate further on what you are thinking?  I will post everything to a github repo so people can play with what I did or even just use it as a reference if they want to do something very different.

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Brian wrote 05/14/2023 at 22:57 point

Very cool!

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Dan Julio wrote 05/18/2023 at 20:05 point

Thank you :-)

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