Overview / Usage

The project aims to develop a non-invasive head positioning system catering to quadriplegic patients who can only tilt their heads. The system utilizes ultrasonic sensors (HCSR04) to measure the head's tilt in both vertical and horizontal directions, enabling the identification of nine distinct head positions. The FPGA-based DE1-SOC is employed for parallel measurements, and the detected positions are displayed using HEX displays and printed for monitoring and medical assessment.

Some advantages of using ultrasonic sensors over accelerometer based positioning systems.

• Contactless and Non-Invasive
• Precise Positioning: Ultrasonic sensors provide accurate and precise distance measurements, enabling the system to detect subtle head tilts in both vertical and horizontal directions.
• Elimination of Drift and Gravity Effects: Accelerometer-based devices are susceptible to drift and gravity effects, which can introduce errors in the tilt measurements over time. Ultrasonic sensors do not suffer from such issues, ensuring consistent and reliable tilt detection, even during extended usage.
• Reduced Sensitivity to Movement: Ultrasonic sensors are less affected by external movements or vibrations since they measure the distance to an object based on the time-of-flight of sound waves. In contrast, accelerometers may pick up unintended movements or vibrations, leading to inaccurate tilt measurements.
• Multi-Axis Detection: The ultrasonic sensor-based system can detect head tilts in both vertical and horizontal axes simultaneously. This allows for precise identification of nine different head positions, providing a more comprehensive assessment of the user's mobility needs.
• Ease of Calibration: Ultrasonic sensors typically require minimal calibration compared to accelerometers, which often require complex calibration procedures to ensure accurate measurements. The reduced calibration process simplifies the setup and configuration of the head positioning system.
• Compatibility with Various Positions: The non-invasive nature of ultrasonic sensors allows for flexibility in system placement. The system can be mounted on various devices or wearables, such as neck pillows or headrests, offering customized solutions to meet individual user preferences.

Methodology / Approach

• Requirement Analysis: The project began with an analysis of the requirements for a non-invasive head positioning system suitable for quadriplegic patients. The specific functionalities, such as tilt measurement in all directions and data display, were identified as key components.
• Ultrasonic Sensor Integration: HCSR04 ultrasonic sensors with 40kHz sonic burst capabilities are chosen for rectilinear distance measurement. Two sensors are employed; one for detecting the chin's position (SU) to deduce vertical tilt and another for left or right tilt (SL). The reference positions for SU and SL are defined.
• FPGA Design and Module Implementation: The DE1-SOC FPGA is utilized for parallel measurement of both tilts. Verilog modules are developed to trigger the sensors, capture echo data, and deduce the tilt angles based on distance measurements from the sensors.
• Tilt Deduction Logic: The Verilog modules incorporate logic to deduce the tilt based on the front distance (FDCM) and side distance (SDCM) measurements obtained from the sensors. By comparing the measured distances with predefined thresholds, the system identifies nine possible head positions (NN, LN, RN, NU, ND, LU, RU, LD, RD).
• N- neutral (FDCM == 5 or SDCM == 14)
  L - left tilt (SDCM > 14)
  R - right tilt (SDCM < 14)
  U- upward tilt (FDCM > 5)
  D - downward tilt (FDCM < 5)
  FDCM- Front distance in cm | SDCM - Side distance in cm
  Note: The reference position of SU is 5 cm below the chin of the user and
  SL is 14 cm from the right earlobe with the sensor mounted on the right
  shoulder tilted ~ 45 degrees upward
• HEX Display and Output Printing: The FPGA interfaces with HEX displays to present the detected head positions. HEX5 and HEX4 display the vertical and horizontal tilts, respectively. Other HEX displays (HEX3 to HEX0) present the measured distances in centimeters and millimeters for monitoring and medical assessment. The position data is also printed for further analysis.
• System Control with Switches: SW9 of the DE1-SOC board serves as the enable signal for triggering the counters and sensors. GPIOs are used for sensor input and output interfacing, allowing flexible I/O operations.
• Testing and Validation: Comprehensive testing and verification are performed to ensure the accuracy and reliability of the system. Various head tilt scenarios are simulated, and the measured positions are cross-verified with the expected outcomes.

Technologies Used

Intel Altera DE1-SoC Board (Cyclone V FPGA)

HC-SR04 Ultrasonic Sensor

Intel Quartus Prime

ModelSim

Verilog HDL

Documents and Presentations

Other links

• HC-SR04 Datasheet