Introduction

A CircuitPython-based Atari Punk Console emulation helper class based on the "Stepped Tone Generator" circuit, "Engineer's Mini-Notebook: 555 Circuits", Forrest M. Mims III (1984).

Dependencies

This driver depends on:

• Adafruit CircuitPython

Please ensure all dependencies are available on the CircuitPython filesystem. This is easily achieved by downloading the Adafruit library and driver bundle or individual libraries can be installed using circup.

Installing to a Connected CircuitPython Device with Circup

Make sure that you have circup installed in your Python environment. Install it with the following command if necessary:

pip3 install circup

With circup installed and your CircuitPython device connected use the following command to install:

circup install cedargrove_punkconsole

Or the following command to update an existing version:

circup update

Usage Example

import board
import analogio
import pwmio
from simpleio import map_range
from cedargrove_punkconsole import PunkConsole

# instantiate a PunkConsole output on pin A1 (PWM-capable)
punk_console = PunkConsole(board.A1, mute=False)

# define the two potentiometer inputs
f_in = analogio.AnalogIn(board.A2)  # Oscillator Frequency
pw_in = analogio.AnalogIn(board.A3)  # One-Shot Pulse Width

while True:
    # read the inputs, map to practical audio ranges, send to PunkConsole instance
    #   oscillator frequency range: 3Hz to 3kHz
    #   one-shot pulse width range: 0.5ms to 5ms
    punk_console.frequency = map_range(f_in.value, 0, 65535, 3, 3000)
    punk_console.pulse_width_ms = map_range(pw_in.value, 0, 65535, 0.5, 5.0)

Documentation

API documentation for this library can be found in PunkConsole_API.

The CedarGrove PunkConsole emulates an astable square-wave oscillator and synchronized non-retriggerable one-shot monostable multivibrator to create the classic stepped-tone generator sound of the Atari Punk Console. As with the original circuit, the oscillator frequency and one-shot pulse width are the input parameters. Instantiation of the Punk Console class will start the output waveform based on the input parameters and enable the output signal if mute=False. If no input parameters are provided, the output signal will be disabled regardless of the mute value. Once instantiated, the class is controlled by the frequency, pulse_width_ms, and mute properties.

This version of the emulator works only with PWM-capable output pins.

Depending on the timer and PWM capabilities of the host MPU board, the emulator can easily outperform the original analog circuit. Oscillator frequency is only limited by the MPU's PWM duty cycle and frequency parameters, which may create output signals well above the practical audio hearing range. Therefore, it is recommended that one-shot pulse width input be limited to the range of 0.5ms and 5ms and that the oscillator frequency input range be between 3Hz and 3kHz -- although experimentation is encouraged!

The repo contains three examples, a simple single-channel console, an annoying stereo noisemaker, and a note table driven sequencer. For the first two examples, input is provided by potentiometers attached to two analog input pins. The sequencer is controlled by an internal list of notes that select the oscillator frequency; pulse width is potentiometer controlled.

• Minimum and maximum input ranges (may be further limited by the MPU):

  • pulse_width: 0.05ms to 5000ms
  • frequency: 1Hz to >4MHz

• Practical input ranges for audio (empirically determined):

  • pulse_width: 0.5ms to 5ms
  • frequency: 3Hz to 3kHz

The CedarGrove Punk Console algorithm uses PWM frequency and duty cycle parameters to build the output waveform. The PWM output frequency is an integer multiple of the oscillator frequency input compared to the one-shot pulse width input:

pwm_freq = freq_in / (int((pulse_width) * freq_in) + 1)

The PWM output duty cycle is calculated after the PWM output frequency is determined. The PWM output duty cycle is the ratio of the one-shot pulse width and the wavelength of the PWM output frequency:

pwm_duty_cycle = pulse_width * pwm_freq

Planned updates:

For non-PWM analog output, use audiocore with a waveform sample in the RawSample binary array, similar to the simpleio.tone() helper. The output waveform's duty cycle will be adjusted by altering the contents of the array, perhaps with ulab to improve code execution time. The audiocore.RawSample.sample_rate frequency is expected to be directly proportional to the original algorithm's PWM frequency output value, calculated from the sample_rate divided by the length of the audiocore.RawSample array (number of samples).

MIDI control: A version that uses USB and/or UART MIDI is in the queue. Note that the PunkConsole.mute property could be used for note-on and note-off. note_in_example.py shows how muting can be used for individual notes.

CV control: A Eurorack version was discussed, it's just a bit lower on the to-do list, that's all. But you know, the first two examples use analog inputs (0 to +3.3 volts) for frequency and pulse width control. Just sayin'.

For information on building library documentation, please check out this guide.

Contributing

Contributions are welcome! Please read our Code of Conduct before contributing to help this project stay welcoming.