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Call blocker HW and SW requirements

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Newbie level 1
Jan 3, 2017
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I’d like to build a device that act as a call handler and blocker over analog telephone lines with the least possible BoM (Bill of Materials).
The device should be connected in cascade with the analog telephone to the analog line or POTS terminal so one terminal should be configured as FXO (connected to the PSTN) and the other one as FXS (connected to the analog phone).
The device should be able to:

  1. Answer an incoming call.
  2. Allow an outgoing call to be issued by the phone connected to the device while understanding some key DTMF tones for eventual internal processing.
  3. Read the CLIP (or detect the call was sent as withheld or with no CLIP)
  4. Compare the CLIP with a white list and with a black list (which of course needs to be maintained)
    1. If the CLIP belongs to the while list the incoming call is passed directly to the phone and the phone will ring
    2. If the CLIP belongs to the black list the call is rejected with a pre-recorded message
    3. If the CLIP is in neither of the two lists, the device must pick up the call, play a welcome message and ask the caller to say its name, then it will put the incoming call on-hold, it will ring the phone and play the voice of the caller. The called person through DTMF will decide to pick up the call, pick up the call & save the CLIP into the white list, reject the call, reject the call & save the CLIP into the black list or, simply ignore it by putting its telephone on hook.
    4. The device with also be capable to handle incoming calls being sent as withheld or with no CLIP
  5. It must also function as an answering machine by accepting a message from the caller and play it at a later time to the called person.
  6. The device should be programmed through:
    1. The phone (DTMF). Only main vital functions.
    2. A PC’s Web Interface connected to the device through a USB interface. All functions such as the list management and some troubleshooting functions (call logs, device logs, etc.), firmware management and advanced configuration
  7. The device should allow to record the conversation into an external SD memory
The device should be able to handle the following type of memories:

  1. Non volatile memory for the firmware, PCM messages, logs and program flags
  2. RAM
  3. An external SD memory to record the conversation
This is basically what I would need to develop.
I’d like to know the circuit diagram of a prototype with the above mentioned features and the best suitable program language and framework to develop the software according to the chosen prototype.
Thanks in advance.

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