GPS PPS + LIDAR Signal Generator for HIL development and testing.

ESP32-based Ground Support Equipment (GSE) for Hardware-in-the-Loop (HIL) development and testing of subsystems that process PPS and LIDAR data

This project provides a cost-effective GSE solution using ESP32 microcontroller to generate timing signals for HIL testing of subsystems that process PPS and LIDAR data:

• PPS Signal: 1Hz Pulse Per Second with 100ms pulse width for GPS time synchronization
• LIDAR Signal: 20Hz with configurable Gaussian jitter for realistic sensor timing variations
• Configurable Parameters: Easy modification of timing values for different HIL testing scenarios

Purpose: HIL Testing GSE

This signal generator serves as Ground Support Equipment (GSE) for Hardware-in-the-Loop (HIL) testing of subsystems without requiring actual GPS and LIDAR hardware:

• HIL Testing: Test complete subsystems in a controlled environment with simulated sensor inputs
• Hardware Integration: Validate subsystem hardware interfaces and timing requirements in HIL setup
• Jitter Testing: Simulate realistic sensor timing variations for subsystem validation
• Integration Testing: Test complete subsystem behavior with simulated signals in HIL environment
• Cost-Effective HIL: Avoid expensive GPS and LIDAR hardware during HIL development and testing

Key Features

• Hardware-based signal generation using ESP32 LEDC for precise timing
• Configurable Gaussian jitter for realistic LIDAR timing variations
• Dual independent signals with separate GPIO outputs
• Easy configuration through compile-time parameters
• PlatformIO/ESP-IDF compatible for straightforward development

HIL Testing Use Cases

This GSE is designed for Hardware-in-the-Loop (HIL) testing scenarios where you need to process PPS and LIDAR data:

• HIL Subsystem Testing: Test complete subsystems in controlled HIL environment with simulated sensor inputs
• Hardware Integration: Validate subsystem hardware interfaces and signal processing capabilities in HIL setup
• Timing Synchronization: Validate subsystem timing requirements and synchronization behavior in HIL environment
• Jitter Handling: Test subsystem response to realistic sensor timing variations in HIL testing
• HIL Integration Testing: Validate complete subsystem behavior without real GPS/LIDAR hardware in HIL environment
• Performance Testing: Measure subsystem performance with consistent timing inputs in HIL setup
• Interface Validation: Test subsystem communication protocols and data handling in HIL environment

Technical Implementation

The GSE uses ESP32 hardware for reliable signal generation:

• PPS Signal: ESP32 LEDC hardware PWM for consistent 1Hz timing
• LIDAR Signal: ESP32 hardware timers with configurable Gaussian jitter for realistic variations
• Independent Operation: Separate LEDC timers prevent signal interference
• Configurable Parameters: Easy adjustment of timing and jitter through code constants

How It Works

The code uses a hybrid approach for signal generation:

1. PPS Signal (1Hz)

   • Uses LEDC_TIMER_0 and LEDC_CHANNEL_0
   • Configured in LOW_SPEED_MODE (sufficient for 1Hz)
   • Output on GPIO 4
   • 100ms pulse width (10% duty cycle)
   • Hardware PWM for precise timing

2. LIDAR Signal (20Hz) with Jitter

   • Uses hardware timer (GPTimer) for precise timing
   • Output on GPIO 21
   • 5ms pulse width with 1μs resolution
   • Configurable Gaussian jitter for realistic timing variations
   • Each pulse has independent random timing variation

Both signals use hardware-based generation for maximum precision and efficiency.

Why This Design?

1. Hardware-Based Approach for Maximum Performance

   • PPS signal: Hardware PWM for maximum precision (GPS synchronization)
   • LIDAR signal: Hardware timer (GPTimer) for precise timing with configurable jitter
   • Both signals use dedicated hardware for optimal performance

2. Jitter Implementation

   • Gaussian distribution for realistic timing variations
   • Configurable mean and standard deviation
   • Clamping to prevent extreme values
   • Independent jitter for each pulse
   • Hardware timer ensures precise timing even with jitter

3. Configurable Parameters

   • All timing parameters are defined at the top of the file
   • Jitter parameters easily adjustable
   • No need to change code logic for different timing requirements

Customization

Changing Signal Parameters

All timing parameters are defined at the top of src/main.c:

// Timing parameters
#define PPS_FREQ_HZ 1        // PPS frequency in Hz
#define PPS_PULSE_MS 100     // PPS pulse width in milliseconds
#define LIDAR_FREQ_HZ 20     // LIDAR frequency in Hz
#define LIDAR_PULSE_MS 5     // LIDAR pulse width in milliseconds

// Jitter configuration for LIDAR pulse
#define LIDAR_JITTER_ENABLED 1           // Enable/disable jitter (1=enabled, 0=disabled)
#define LIDAR_JITTER_MEAN_MS 0.0         // Mean jitter in milliseconds (0.0 = no bias)
#define LIDAR_JITTER_STDDEV_MS 0.5       // Standard deviation of jitter in milliseconds
#define LIDAR_JITTER_MAX_MS 2.0          // Maximum jitter value in milliseconds (clamping)

// Pulse polarity configuration
#define PPS_POLARITY_ACTIVE_HIGH 1       // PPS pulse polarity (1=active high, 0=active low)
#define LIDAR_POLARITY_ACTIVE_HIGH 1     // LIDAR pulse polarity (1=active high, 0=active low)

Changing GPIO Pins

Pin assignments can be modified in the pin definitions:

#define PPS_PIN GPIO_NUM_4
#define LIDAR_PIN GPIO_NUM_19

Jitter Configuration

The LIDAR signal includes configurable random jitter for realistic timing variations:

• LIDAR_JITTER_ENABLED: Set to 1 to enable jitter, 0 to disable
• LIDAR_JITTER_MEAN_MS: Mean jitter value (0.0 = no bias)
• LIDAR_JITTER_STDDEV_MS: Standard deviation of jitter (controls variation amount)
• LIDAR_JITTER_MAX_MS: Maximum jitter value (prevents extreme timing)

Example configurations:

• No jitter: LIDAR_JITTER_ENABLED 0
• Small jitter: LIDAR_JITTER_STDDEV_MS 0.5 (0.5ms standard deviation)
• Large jitter: LIDAR_JITTER_STDDEV_MS 2.0 (2.0ms standard deviation)
• Biased jitter: LIDAR_JITTER_MEAN_MS 1.0 (1ms positive bias)

Pulse Polarity Configuration

Both PPS and LIDAR signals support configurable polarity:

• PPS_POLARITY_ACTIVE_HIGH: Set to 1 for active-high pulses, 0 for active-low
• LIDAR_POLARITY_ACTIVE_HIGH: Set to 1 for active-high pulses, 0 for active-low

Example configurations:

• Active-high pulses (default): PPS_POLARITY_ACTIVE_HIGH 1, LIDAR_POLARITY_ACTIVE_HIGH 1
• Active-low pulses: PPS_POLARITY_ACTIVE_HIGH 0, LIDAR_POLARITY_ACTIVE_HIGH 0
• Mixed polarity: PPS active-high, LIDAR active-low

Duty Cycle Calculation

The duty cycle is automatically calculated based on the frequency and pulse width:

#define PPS_DUTY ((PPS_PULSE_MS * PPS_FREQ_HZ * (1 << LEDC_RESOLUTION)) / 1000)```

## Quick Start

### Hardware Requirements

- **ESP32 Development Board** (ESP32, ESP32-S2, ESP32-S3, or ESP32-C3)
- **USB Cable** for programming and power
- **Oscilloscope or Logic Analyzer** for signal verification (optional)
- **Breadboard and Jumper Wires** for connections

### Software Requirements

- **PlatformIO IDE** (recommended) or **ESP-IDF**
- **Git** for cloning the repository
- **ESP32 Toolchain** (automatically installed with PlatformIO)

### Installation and Setup

1. **Clone the repository**:
   ```bash
   git clone https://github.com/yourusername/pps-gen.git
   cd pps-gen

2. Open in PlatformIO:

   • Install PlatformIO IDE or use PlatformIO Core
   • Open the project folder

3. Build and Upload:

   platformio run --target upload

4. Monitor Output (optional):

   platformio device monitor

Signal Verification

PPS Signal (GPIO 4):

• Frequency: 1.000 Hz (exact)
• Pulse Width: 100ms
• Duty Cycle: 10%
• Polarity: Configurable (active high/low)

LIDAR Signal (GPIO 21):

• Frequency: 20 Hz (with configurable jitter)
• Pulse Width: Configurable duty cycle
• Jitter: Gaussian distribution with configurable parameters
• Polarity: Configurable (active high/low)

Testing with Oscilloscope

1. Connect probes to GPIO 4 (PPS) and GPIO 21 (LIDAR)
2. Verify PPS timing: Should show exactly 1.000 Hz with 100ms pulses
3. Test LIDAR jitter: Enable jitter and observe timing variations
4. Measure accuracy: Use high-resolution oscilloscope for microsecond precision verification

Troubleshooting

• If signals are not appearing, check:
  • GPIO pin connections
  • Power supply to ESP32
  • Serial monitor for any error messages
• If timing is inaccurate:
  • Verify the ESP32's clock configuration
  • Check for any interference on the GPIO pins
• If jitter behavior is unexpected:
  • Verify jitter parameters are within reasonable ranges
  • Check that LIDAR_JITTER_MAX_MS is not too restrictive
  • Ensure LIDAR_JITTER_STDDEV_MS is positive

Technical Specifications

Parameter	PPS Signal	LIDAR Signal
Frequency	1.000 Hz	20 Hz (base)
Pulse Width	100ms	Configurable
Duty Cycle	10%	Configurable
GPIO Pin	GPIO 4	GPIO 21
Timing Precision	Hardware PWM	Hardware Timer
Jitter	None	Gaussian (configurable)
Polarity	Configurable	Configurable

GSE Performance

• Timing Accuracy: Consistent timing suitable for software development and testing
• Jitter Simulation: Gaussian distribution with configurable parameters for realistic testing
• Low Cost: ESP32-based solution for cost-effective development
• Easy Setup: Simple configuration and deployment for development environments
• Reliable Operation: Hardware-based timing ensures consistent signal generation

Advanced Configuration

Jitter Parameters

The LIDAR signal supports sophisticated jitter modeling:

#define LIDAR_JITTER_ENABLED 1           // Enable/disable jitter
#define LIDAR_JITTER_MEAN_MS 0.0         // Mean jitter (bias)
#define LIDAR_JITTER_STDDEV_MS 5.0       // Standard deviation
#define LIDAR_JITTER_MAX_MS 15.0         // Maximum jitter (clamping)

Development Configuration

• Hardware PWM: Reliable PPS signal generation
• ESP Timer: Precise LIDAR timing with jitter simulation
• Independent Channels: Separate signal generation without interference
• Easy Configuration: Adjustable parameters for different testing scenarios

License

This project is open source and available under the MIT License.

Contributing

Contributions are welcome! This GSE project follows embedded systems best practices:

• Clean Code: Allman bracket style, comprehensive documentation
• Modular Design: Deterministic, no heap allocation
• Hardware Focus: Direct hardware control for reliable operation
• Testing: Hardware verification with oscilloscope recommended

Development Guidelines

• Follow ESP32/ESP-IDF coding standards
• Document all functions with purpose and behavior
• Use hardware-based solutions for consistent operation
• Test with actual hardware and oscilloscope verification

Keywords

ESP32, PPS, LIDAR, signal generator, GSE, ground support equipment, HIL testing, hardware-in-the-loop, subsystem development, GPS synchronization, embedded systems, timing simulation, hardware PWM, ESP-IDF, PlatformIO, Gaussian jitter, sensor testing, data processing, subsystem integration, hardware testing, signal processing subsystems, HIL development