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SIMCOM Voice Dialer (SIM7500 / SIM7600 Series)

AI Assistance Disclosure

This project was developed with the assistance of AI tools to accelerate development, improve code quality, and explore design approaches.

Scope of AI Assistance

AI was used as a development aid in the following areas:

  • Generating initial code structures and boilerplate
  • Assisting with AT command handling patterns and parsing logic
  • Helping design class architecture and separation of concerns
  • Providing suggestions for error handling and edge cases
  • Assisting in documentation and README creation

Human Oversight

All AI-generated code was:

  • Reviewed and validated before integration
  • Tested against real hardware (SIMCOM modules)
  • Modified where necessary to ensure correctness and reliability

Final implementation decisions, debugging, and system design was performed myself.

Notes

AI was used as a tool—not a replacement for understanding. If something breaks, that responsibility still belongs to the human holding the keyboard.

Description

A Windows-based C# application for controlling SIMCOM LTE modules, providing voice calling, real-time audio streaming, and SMS functionality via AT commands.

This project interfaces directly with SIMCOM modems over USB serial ports and bridges live audio using NAudio.

Features

  • Voice call control (dial, answer, hang up)
  • Real-time audio streaming (microphone ↔ modem ↔ speakers)
  • SMS send, receive, read, and delete
  • Call waiting (enable/disable/query)
  • Call forwarding (multiple conditions)
  • Automatic COM port detection via USB device IDs
  • AT command abstraction layer with URC parsing

Project Structure

SIMCOMVoiceDialer/
│
├── Program.cs                # Console UI / entry point
├── SerialAudioPhone.cs      # High-level controller
├── ModemControl.cs          # AT command + serial handling
├── AudioBridge.cs           # Audio streaming (NAudio)
├── SmsManager.cs            # SMS handling + parsing
├── SmsMessage.cs            # SMS data model
├── CallForwardReason.cs     # Call forwarding enum

Key components:

  • SerialAudioPhone – orchestrates modem, audio, and SMS
  • ModemControl – handles AT communication
  • AudioBridge – manages PCM audio streaming
  • SmsManager – parses and manages SMS

Requirements

Hardware

  • SIMCOM LTE module (SIM7500 / SIM7600 series)
  • USB connection exposing:
  • AT command port (e.g., MI_02)
  • Audio port (e.g., MI_04)
  • Microphone and speakers

Software

  • Windows 10/11
  • .NET 6.0 or newer
  • Visual Studio 2022 (recommended) or .NET CLI

NuGet package:

  • NAudio

Getting Started

1. Clone the Repository

git clone https://github.com/yourusername/SIMCOMVoiceDialer.git
cd SIMCOMVoiceDialer

2. Install Dependencies

If using .NET CLI:

dotnet add package NAudio

Or via Visual Studio:

  • Right-click project → Manage NuGet Packages → Install NAudio

3. Connect the Modem

Plug in your SIMCOM device via USB. The application automatically detects ports using:

  • AT Port: VID_1E0E&PID_9005&MI_02
  • Audio Port: VID_1E0E&PID_9005&MI_04

No manual COM configuration required.

4. Build the Project

Option A – Visual Studio

  1. Open the solution/project
  2. Set build target to x64 (recommended)
  3. Press Build → Build Solution

Option B – .NET CLI ` dotnet build

5. Run the Application

Visual Studio

Press F5 or Start Without Debugging

` dotnet run

Usage

Once running, you’ll see the main menu:

++++++++++ Main Menu ++++++++++
D - Dial
A - Answer
H - Hang up
F - Call forwarding
W - Call waiting
S - SMS menu
Q - Quit

Example: Dial a Call

` Enter number to dial: +123456789

Example: Send SMS

Enter recipient: +123456789
Enter SMS text: Hello from SIM7600

Configuration

Default Settings

  • Baud rate: 115200
  • Audio format: 8000 Hz, mono PCM
  • Echo suppression factor: 0.5

Initialization Commands

Executed automatically:

  • AT+CLIP=1 (Caller ID)
  • Audio gain configuration
  • SMS text mode setup
  • Network registration settings

How It Works

  • The modem communicates over UART/USB using AT commands (default 115200 baud)
  • Audio is streamed through a secondary serial interface using PCM
  • URCs (like RING, +CMT) are parsed in real-time
  • NAudio handles microphone capture and speaker playback

Known Limitations

  • Windows-only (uses WMI for device detection)
  • Assumes SIMCOM USB interface layout is consistent
  • Uses blocking delays (Thread.Sleep) in some areas
  • Basic phone number validation
  • Limited retry/error recovery logic

Troubleshooting

Modem Not Detected

  • Verify USB drivers are installed
  • Check Device Manager for COM ports
  • Confirm device IDs match expected values

No Audio

  • Ensure correct microphone/speaker devices are available
  • Confirm modem supports PCM audio over USB
  • Check that audio port is opening successfully

SMS Not Receiving

Verify:

  • AT+CNMI=2,2,0,0,0 is active
  • Network registration is complete

References

  • SIMCOM AT Command Manual
  • SIMCOM UART Application Note
  • NAudio Documentation