rotary-phone-reader

Micropython code for your embedded project to read dialled numbers from a rotary phone. Use an old phone as an input device for your retro-futuristic project.

I designed this for an ESP32 board, but I think any board that is supported by the micropython machine module will work.

This code is interrupt-driven so your main program is free to do whatever you want. You can poll for a dialed number, or register a callback to run once a number is dialed.

WORK IN PROGRESS

2024-11-10 - This is a work in progress. It's almost done, but give it another month for it to be production-ready.

Installation

Copy this to your /lib/ folder and you're ready to go.

This has no dependencies beyond machine and time that are already part of micropython.

Getting Started

Sample programs:

polling

import time
from pulse_decoder import retrieve_dialed_number, gpio_pin_number

gpio_pin_number = 14
def main():
    while True:
        # Check periodically for a completed phone number
        dialed_number = retrieve_dialed_number()
        if dialed_number:
            print("Detected dialed phone number:", dialed_number)
            if dialed_number[0] == 1:
                # 1 - ABC - Play ABBA
                pass
            elif dialed_number[0] == 2:
                # 2- DEF - Play Debussy
                pass
            elif dialed_number == (8,6,7,5,3,0,9):
                # Play Tommy Tutone "867-5309/Jenny"
                pass

        # Sleep for a bit to avoid excessive polling
        time.sleep(0.1)

interrupt-driven

import time
from pulse_decoder import register_callback, gpio_pin_number

gpio_pin_number = 14

def dialed_number_callback(dialed_number):
    if dialed_number:
        print("Detected dialed phone number:", dialed_number)
        if dialed_number[0] == 1:
            # 1 - ABC - Play ABBA
            pass
        elif dialed_number[0] == 2:
            # 2 - DEF - Play Debussy
            pass
        elif dialed_number == (8,6,7,5,3,0,9):
            # Play Tommy Tutone "867-5309/Jenny"
            pass

def main():
    # do some stuff
    register_callback(dialed_number_callback)
    # do more stuff

Configurable items

• gpio_pin_number - integer - Which ESP32 GPIO pin you want to use. Must support an internal pull-up resistor.
• virtual_timers - boolean - Whether your device supports virtual timers. (default False. The ESP32 does not.) The program will choose timers 0, and 1. You can change those too, if you want.
• Various pulse characteristics if you really want *DURATION*, *DELAY*, *TIMEOUT*, *TOLERANCE*. But you should not have to touch them.

Debugging

This should "just work", but if your specific phone's characteristics are different from those expected, you may need to tweak the code a little. There are commented-out print statements you can uncomment to (To make the code as fast as possible in interrupt-context, these are left as commented rather than if-statements.)

Further Reading

References

• https://en.wikipedia.org/wiki/Pulse_dialing
• https://www.dialogic.com/webhelp/csp1010/8.4.1_ipn3/dev_overview_dsp_one_-_e1_dial_pulse_address_signaling.htm
• https://www.3amsystems.com/World_Tone_Database/Signalling_guide?q=Pulse_dialing
• https://fahrplan.events.ccc.de/congress/2023/fahrplan/system/event_attachments/attachments/000/004/462/original/analog_phones.pdf

Installing micropython modules on your ESP32

From the REPL:

import os
os.mkdir "lib" # Just once

import mip
mip.install("xmltok") # For example

Unit testing

There is no unit testing. It's so hardware-dependent that I never Mock-ed it all up. Just load it on your ESP32 and test.