## **Lab 2** | Working with Sensors on Raspberry Pi

### Design of Autonomous Systems  
### CSCI 6907/4907 - Section 86  
### Prof. **Sibin Mohan**

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## Objectives

- Understand how sensors communicate with Raspberry Pi.  
- Work with onboard Navio2 sensors.  
- Integrate and test an external ultrasonic sensor.

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## Equipment Required  
- Raspberry Pi 4B (or similar)  
- Navio2 Shield (with header pins, spacers, and screws)  
- MicroSD Card (32GB or larger)  
- USB to UART Cable  
- Power Supply (USB-C)  
- HC-SR04 Ultrasonic Sensor  
- Jumper Wires

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## Basic Linux Shell Commands

### General Commands  
- `ls`, `cd`, `pwd`, `mkdir`, `rm`, `cp`, `mv`, `cat`, `nano`

### Raspberry Pi-Specific  
- `raspi-config`: Configure SSH, Wi-Fi, etc.

### Navio2-Specific  
- `emlidtool`: Check the status of Navio2 sensors.

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## How Devices Communicate

### GPIO Overview  
- General-purpose input/output pins for connecting devices.  
- Protocols:  
  - **I2C**: Used for Navio2 sensors.  
  - **SPI, UART**: For high-speed or serial communication.

### Devices in Linux  
- Devices represented as files (e.g., `/dev/gpio`).  
- Interact via libraries or directly through shell commands.

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## Navio2 Sensors Overview

### Key Features  
- **Accelerometer**: Measures acceleration.  
- **Gyroscope**: Tracks rotation/tilt.  
- **Magnetometer**: Compass for magnetic north.  
- **Barometer**: Measures altitude.  
- **GPS**: Tracks location.  
- **PWM Outputs**: Drives motors and servos.

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## Onboard Sensor Testing

1. Assemble Navio2 shield on Raspberry Pi.  
2. Verify functionality using:  
   ```bash
   sudo emlidtool
   ```

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## Explanation of Accelerometer Code

- **Library Imports**:  
  - `navio2.mpu9250`: Interacts with the accelerometer.  
  - `time`: Adds delays for consistent data collection.

- **Initialization**:  
  - `imu = navio2.mpu9250.MPU9250()`: Creates a sensor instance.  
  - `imu.initialize()`: Prepares the sensor for data collection.

- **Data Collection**:  
  - `imu.getMotion9()`: Reads acceleration in X, Y, and Z axes.

- **Output**:  
  - Prints acceleration values in a readable format.  
  - Adds a 1-second delay for clarity between readings.

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## Using an External Ultrasonic Sensor

### Connections  
- `VCC` → `5V`  
- `GND` → `GND`  
- `TRIG` → GPIO18  
- `ECHO` → GPIO24

### Validation  
- Measure distances using Python scripts.  
- Real-time output to verify accuracy.

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## Explanation of Ultrasonic Sensor Code

- **Pin Setup**:  
  - `TRIG` → GPIO18: Trigger pin to send sound waves.  
  - `ECHO` → GPIO24: Receives the reflected echo.

- **Working Principle**:  
  - **Trigger Pulse**: Sends a short ultrasonic pulse (10 μs).  
  - **Echo Measurement**: Measures the time taken for the echo to return.

- **Distance Calculation**:  
  - Time (duration) × Speed of Sound (343 m/s) ÷ 2.  
  - Divided by 2 because the wave travels to the object and back.

- **Real-Time Output**:  
  - Continuously measures and prints distance in centimeters.

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## Assignment Question: Understanding Ultrasonic Sensors

Write a detailed paragraph explaining how an ultrasonic sensor works. Your explanation should include:

- The basic principle behind ultrasonic sensing.  
- The role of the **trigger** and **echo** pins.  
- How distance is calculated using the time taken for sound waves to travel.  
- Any real-world applications where ultrasonic sensors are commonly used.

## Submission Guidelines:

- Write your response in your own words.  
- Submit as a typed document (**markdown**) by **12 PM tomorrow**.  
- Ensure clarity and conciseness (**150-200 words**).

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## Summary

- Configured and tested **Navio2 onboard sensors**.  
- Integrated an **external ultrasonic sensor**.  
- Verified real-time data collection from all sensors.