Fone

fone

A modern take on the classic Nokia cell phone experience, built with a Raspberry Pi Pico 2 running MicroPython. This project combines the simplicity and reliability of old-school Nokia phones with quality-of-life improvements for modern usability.

Overview

fone is a DIY cellular phone that captures the essence of classic Nokia devices while incorporating modern components and conveniences. The device features a minimalist design focused on essential communication functions: calls, SMS, and basic navigation, all powered by MicroPython for easy customization and development.

Hardware Components

Core Processing

• Raspberry Pi Pico 2 - Main microcontroller running MicroPython
• W25Q128 SPI Flash - 16MB flash storage for contacts, messages, and system data

Cellular Communication

• SIM7600G Module - 4G/LTE cellular connectivity with GPS
• Connected via UART (TX/RX) to Pico 2

Power Management

• 3700mAh Lithium Battery - Long-lasting power source
• TP4056 Charging Module - Safe battery charging via USB-C
• MT3608 Boost Converter - Boost LiPo battery to 5v for use by the SIM module and Pico

Audio System

• MAX98357A I2S Amplifier - Digital audio amplification
• 1W 8Ω Speaker - Clear audio output for calls and notifications
• GY-MAX4466 Electret Microphone - Voice input with AGC
• ADS1115 ADC - High-resolution analog-to-digital conversion for microphone

Display & Input

• 2.42" OLED Display (SSD1309) - monochrome, 128x64 resolution, SPI interface, low power consumption
• ANO Directional Navigation and Scroll Wheel Rotary Encoder - Navigation, selection, scroll, and menu control
• 3V Coin Vibration Motor - Haptic feedback and notifications

Features

Core Functionality

• Voice Calls - Make and receive phone calls with clear audio
• SMS Messaging - Send and receive text messages
• Contact Management - Store and organize phone contacts
• Call History - Track incoming, outgoing, and missed calls

Enhanced User Experience

• Improved Text Input - Modern T9-style predictive text with encoder navigation
• Menu Navigation - Intuitive interface designed for encoder and directional button control
• Scroll Wheel Support - Rotary encoder provides smooth scrolling through lists and menus
• Low Power Operation - E-paper display and efficient power management
• Haptic Feedback - Vibration for notifications and user interactions

Additional Features

• GPS Location (Stretch Goal) - Built-in positioning via SIM7600G
• Battery Monitoring - Real-time battery level and charging status
• Silent/Vibrate Modes - Customizable notification preferences
• Basic Games - Classic Nokia-style entertainment (Snake, etc.)

Technical Specifications

Connectivity

• Cellular: 4G LTE via SIM7600G
• GPS (Stretch Goal): Built-in GNSS receiver
• Storage: 16MB SPI flash memory (W25Q128)

Power

• Battery Life: All-day usage with 3700mAh capacity
• Charging: USB charging via TP4056 module
• Standby: Ultra-low power consumption with e-paper display

Interface

• Display: 2.42" monochrome OLED (128x64px)
• Input: ANO rotary encoder with directional navigation buttons
• Audio: Full-duplex voice communication
• Feedback: Vibration motor for alerts

Software Architecture

• Platform: MicroPython on Raspberry Pi Pico 2
• Modular Design: Separate modules for cellular, audio, display, and input handling
• Event-Driven: Efficient power management through interrupt-based operation
• Extensible: Easy to add new features and customize behavior

Wiring Guide

SIM7600G to Raspberry Pi Pico 2

The SIM7600G module connects via UART and requires the following connections:

Key Points:

• Power: SIM7600G requires 5V via MT3608 boost converter for proper RF operation
• Current Draw: Module can draw up to 2A during transmission bursts
• UART: Cross-connect TX/RX (module TX → Pico RX, module RX → Pico TX)
• Power Key: Pull HIGH briefly to turn module on/off
• Status: Monitor this pin to check if module is powered and ready
• Dual Ground: Connect both ground pins for stable operation

ANO Directional Navigation and Scroll Wheel Rotary Encoder

The primary input is an ANO directional navigation and scroll wheel rotary encoder, providing directional control, rotary scroll input, and a center-press button.

Key Points:

• Rotary Encoder: ENCA/ENCB provide quadrature signals for scroll wheel functionality
• Digital Buttons: All switch pins (SW1-SW5) are simple digital inputs
• Wiring: Connect the COM pin to GND and configure each GPIO pin as an input with an internal pull-up resistor
• Active Low: Button presses and encoder transitions pull pins to ground (LOW)
• Quadrature Decoding: Software tracks encoder A/B state changes to determine rotation direction and steps

Dual Analog Joysticks via ADS1115 ADC

Note: This component has been deprecated and replaced by the ANO Directional Navigation and Scroll Wheel Rotary Encoder.

The phone uses two analog joysticks for navigation and input, connected through an ADS1115 16-bit ADC for full 4-channel analog precision.

ADS1115 ADC Module:

Left Joystick (mounted upside down):

Right Joystick:

Key Points:

• Full Analog Control: ADS1115 provides 4 channels of 16-bit ADC precision
• I2C Address: 0x48 (ADDR pin to GND), can be changed for multiple modules
• Left Joystick: Mounted upside down, so Y-axis values are inverted in software
• ADC Resolution: 16-bit (±32767) with ±4.096V input range matches 5V joysticks
• Switches: Active low with internal pull-up resistors on Pico pins (3.3V logic)
• Update Rate: ~128 SPS (samples per second) for smooth control

3V Vibration Motor

The vibration motor provides haptic feedback for notifications and user interactions.

Option 1: Direct GPIO Control (Recommended to try first)

For Low Current Motors (< 40mA):

Option 2: Transistor-Protected Control

For Higher Current Motors (> 40mA) or if direct control fails:

Transistor Circuit (NPN - 2N2222 or similar):

Key Points:

• Motor Specs: 3V, 12000 RPM, small coin-type vibration motor
• Current Draw: Small motors (17-35mA) can connect directly, larger motors (60-105mA) need transistor
• Pico GPIO Limits: ~16mA safe, ~50mA maximum per pin
• Try Direct First: Start with Option 1 - if motor doesn't work well or Pico gets warm, use Option 2
• Flyback Diode: Optional 1N4001 diode across motor (cathode to +, anode to -) for back-EMF protection
• Control: PWM control via GP16 allows variable vibration intensity
• Frequency: Typical vibration patterns: short bursts (100-300ms) for notifications

2.42" OLED Display (SSD1309)

The 2.42" monochrome OLED display provides the main user interface with a 128x64 resolution using SPI communication.

Display Module Connections:

Key Points:

• SPI Interface: Uses SPI1 on Pico 2 for communication
• Monochrome Display: Black and white output with high contrast
• Resolution: 128x64 pixels provides clear text and simple graphics
• Fast Updates: ~10ms refresh time for full screen updates
• Low Power: Efficient power consumption (perfect for phone standby)
• Rotation Support: Software rotation for portrait or landscape orientation
• Viewing Angle: Wide viewing angle (>160°) for clear visibility
• Compact Size: 2.42" diagonal with minimal bezel

W25Q128 SPI Flash Memory Module

The W25Q128 provides 16MB (128Mbit) of non-volatile storage for contacts, messages, and system data, connected via SPI interface. This flash memory offers faster access times and lower power consumption compared to SD cards.

W25Q128 Module Connections:

Key Points:

• Shared SPI Bus: Uses SPI1 shared with the e-paper display (SLK, D0 pins)
• Separate MISO: Flash memory has its own MISO line (D1/GP8) since display is write-only
• Unique CS: Each device has its own chip select (Flash: GP7, Display: GP9)
• Power: 3.3V operation, low power consumption (4mA active, <1µA standby)
• Storage: 16MB of flash memory with 100,000+ erase/program cycles
• Performance: Up to 104MHz SPI clock, much faster than SD card access
• File System: Can use LittleFS or FAT filesystem via MicroPython's VFS

MAX98357A I2S Amplifier and Speaker

The MAX98357A is a digital I2S audio amplifier used to drive the speaker for calls, notifications, and other audio feedback.

MAX98357A Module Connections:

Speaker Connection:

Key Points:

• I2S Audio: Digital audio provides clear, noise-free sound.
• Power: Connected to 5V for maximum speaker volume.
• Shutdown Pin: GP21 controls the amplifier's shutdown mode to conserve power.
• Mono Output: Although the module has L/R outputs, it's a mono amplifier. Connect speaker to either pair.
• Gain Control: The GAIN pin can be used to adjust the amplification level if needed. Default (unconnected) is 9dB.

GY-MAX4466 Electret Microphone

The GY-MAX4466 microphone module with automatic gain control (AGC) is used for voice input. It's connected directly to one of the Pico's ADC pins.

Microphone Module Connections:

Key Points:

• Direct ADC Connection: Simplifies wiring and reduces component count.
• Analog Pin: Uses GP28, one of the Pico's three dedicated ADC pins.
• Power: Runs on 3.3V power provided by the Pico.
• AGC: The MAX4466's automatic gain control adjusts for varying sound levels.

Battery Level Monitoring

To monitor the battery level, a voltage divider is used to scale the battery's voltage (3.0V-4.2V) down to a range the Pico's ADC can safely read (0-3.3V). The reading is taken on the now-available ADC pin.

Voltage Divider Circuit:

A 1:1 ratio (e.g., two 100kΩ resistors) is simple and effective.

Pin Connection:

Key Points:

• Voltage Divider: Essential to prevent damage to the Pico's ADC.
• Resistor Choice: Using identical resistors (e.g., 100kΩ) creates a simple 1:2 divider. The actual voltage is 2 * adc_voltage.
• ADC Reading: The software must read the analog value from GP26 and multiply it by the divider ratio to calculate the true battery voltage.

[Development in progress - setup instructions coming soon]