audiofone

Stand-alone phone audio interface.

Prerequisites:

raspberry pi target box

• running Raspberry Pi OS lite
• ssh enabled and accessible with default pi/raspberry login
• can do this by touching ssh file on boot partition:
• touch /boot/ssh
• mounted USB flash drive
• see README-config.md

dev box

• debian trixie
• ansible
• ansible.posix
• sshpass

Install:

• update deploy/hosts for correct pibox ip address
• ansible-playbook -i deploy/hosts playbook.yml
• ssh into the box and run alsamixer while doing the tests below
  • aplay /mnt/futel/5852239851.wav
  • have the interface and run them on the real hardware
  • adjust the volume and exit alsamixer
• reboot the pi
  • sudo shutdown -r now

Test on pi:

On boot, supervisord will launch the main audiofone.py app and puredata.

• ensure sd card and USB stick are inserted
• plug in power
• wait about 15-20 seconds for the pi to boot and mount the usb stick
• lift handset, you should hear dialtone
  • if you do not, hear a dialtone, you probably didn't wait long enough after boot. Replace the hookswitch and wait a bit longer and then try again.
• dial one of the numbers of a wav file on the usb stick. You should hear ringing and then audio
• hang up, lift the receiver, do nothing, verify you hear a busy after 15 seconds
• hang up, dial an invalid number, verify that you hear a fast busy after the first invalid keypress
• run alsamixer and verify that your preferred volume persists across reboots

Logs are in /var/log/supervisor/puredata.log and /var/log/supervisor/audiofone.log.

Hardware / Pinouts

• GPIO 7 - pin26 - Hookswitch (other side to ground pin)
• GPIO 17 - pin11 - Input - keypad col 0
• GPIO 27 - pin13 - Input - keypad col 1
• GPIO 22 - pin15 - Input - keypad col 2
• GPIO 12 - pin32 - Output - keypad row 0
• GPIO 16 - pin36 - Output - keypad row 1
• GPIO 20 - pin38 - Output - keypad row 2
• GPIO 21 - pin40 - Output - keypad row 3
• headphone jack -> earpiece audio

pd patch

Audio is played through pd. Python just commands it through OSC (open sound control) messages over local UDP.

listens on port 6066 for osc messages. Pd is run from supervisord, you can steal the command from src/etc/supervisor/conf.d/puredata.conf.