ESP32-Based Intraocular Pressure Monitoring System

A real-time embedded system for non-contact detection of elevated intraocular pressure (IOP) — a primary indicator of glaucoma — using an ESP32 microcontroller, ultrasonic proximity sensing, and barometric pressure acquisition, with live telemetry over a WiFi-hosted HTTP API.

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Table of Contents

• System Overview
• Hardware Requirements
• Pin Configuration
• Dependencies
• Sensor Architecture
• Detection Logic
• HTTP API
• OLED Display Output
• Setup & Flashing
• Configuration
• Known Limitations

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System Overview

The firmware runs on an ESP32 and integrates three peripheral subsystems:

1. HC-SR04 Ultrasonic Sensor — measures distance to the target (e.g., eye/probe surface) in real time using pulse-echo timing.
2. BMP280 Barometric Pressure Sensor (I²C, address 0x76) — reads ambient/contact pressure at 16x oversampling with a 16x IIR filter for stable readings.
3. SSD1306 OLED Display (I²C, address 0x3C, 128×64 px) — renders live diagnostic output: distance, pressure, and detection status.

A motorized pump (GPIO-controlled) is conditionally activated based on proximity threshold. The system also spins up a WiFi-connected HTTP server on port 80, exposing a JSON endpoint for remote sensor polling.

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Hardware Requirements

Component	Part	Interface
Microcontroller	ESP32 (any variant)	—
Pressure Sensor	Bosch BMP280	I²C
Display	SSD1306 128×64 OLED	I²C
Proximity Sensor	HC-SR04 Ultrasonic	GPIO
Actuator	DC Pump / Solenoid	GPIO (digital)

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Pin Configuration

Signal	GPIO Pin
Ultrasonic TRIG	5
Ultrasonic ECHO	4
Pump Control	18
I²C SDA	Default (GPIO 21)
I²C SCL	Default (GPIO 22)

I²C pins use ESP32 Arduino defaults. Override with Wire.begin(SDA, SCL) if using alternate pins.

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Dependencies

Install via Arduino Library Manager or PlatformIO:

Library	Purpose
Adafruit BMP280	Pressure sensor driver
Adafruit SSD1306	OLED display driver
Adafruit GFX	Graphics abstraction layer
WiFi (built-in ESP32)	Network stack
WebServer (built-in ESP32)	HTTP server

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Sensor Architecture

Ultrasonic Distance Measurement

Distance is computed from the round-trip pulse duration using:

distance (cm) = (pulseIn_duration_µs × 0.0343) / 2

Where 0.0343 cm/µs is the speed of sound at room temperature. A 10 µs HIGH pulse on TRIG_PIN initiates the measurement; pulseIn() on ECHO_PIN captures the reflected pulse width.

BMP280 Pressure Acquisition

The BMP280 is initialized in Normal Mode with the following oversampling configuration:

bmp.setSampling(
  MODE_NORMAL,
  SAMPLING_X2,   // Temperature
  SAMPLING_X16,  // Pressure
  FILTER_X16,    // IIR coefficient
  STANDBY_MS_500 // 500 ms standby between measurements
);

Raw pressure is read in Pascals (Pa) and converted to hectopascals (hPa) for display and API output.

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Detection Logic

The system infers elevated IOP risk based on a distance threshold window:

Distance (cm)	Interpretation	Pump State
< 8	Contact / within activation range	HIGH (active)
8 – 10	Glaucoma Detected (IOP threshold zone)	LOW
> 10	Normal / no detection	LOW

Note: The specific distance thresholds (8 cm, 10 cm) are calibrated to the physical probe geometry of the intended deployment. Adjust PUMP_PIN logic and display conditionals accordingly for alternate hardware configurations.

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HTTP API

The ESP32 hosts a lightweight HTTP server on port 80. On successful WiFi connection, the assigned IP address is printed to the Serial monitor.

GET /

Returns a JSON object containing the latest ultrasonic distance and barometric pressure readings.

Response:

{
  "distance_cm": 7.43,
  "pressure": 1013.25
}

Field	Unit	Description
distance_cm	cm	Echo-derived distance to target
pressure	hPa	Barometric pressure from BMP280

Headers:

Access-Control-Allow-Origin: *
Content-Type: application/json

CORS is enabled on all responses to allow cross-origin polling from browser-based dashboards.

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OLED Display Output

The 128×64 SSD1306 display refreshes every 500 ms with three data rows:

Distance:
7.43 cm

Glaucoma Detected     ← or "Glaucoma Not Detected"

Pressure:
1013.25 hPa

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Setup & Flashing

1. Clone or download this repository.
2. Open ESP32_Code.ino in the Arduino IDE (or PlatformIO).
3. Install all listed library dependencies.
4. Set your WiFi credentials in the source:

   const char* ssid = "YOUR_SSID";
   const char* password = "YOUR_PASSWORD";

5. Select your ESP32 board target under Tools → Board.
6. Flash at 115200 baud.
7. Open Serial Monitor to retrieve the assigned IP address.
8. Navigate to http://<device-ip>/ to verify the JSON endpoint.

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Configuration

Constant	Default	Description
TRIG_PIN	5	Ultrasonic trigger pin
ECHO_PIN	4	Ultrasonic echo pin
PUMP_PIN	18	Pump/actuator control pin
SCREEN_WIDTH	128	OLED horizontal resolution
SCREEN_HEIGHT	64	OLED vertical resolution
BMP280 I²C address	0x76	Modify if using 0x77 variant
SSD1306 I²C address	0x3C	Standard address for most modules
Loop delay	500 ms	Sensor polling + display refresh interval

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Known Limitations

• No persistent storage — sensor readings are not logged locally; polling the HTTP endpoint is required for data capture.
• Single-client HTTP server — the WebServer library handles one request at a time; concurrent polling may cause dropped requests.
• No sensor fusion — glaucoma detection is based solely on distance thresholds; pressure readings are displayed but not incorporated into the detection algorithm.
• Speed of sound is temperature-uncorrected — the BMP280 temperature reading is not fed back into the distance calculation. For high-accuracy deployments, apply the temperature-compensated formula.
• WiFi credentials are hardcoded — consider integrating WiFiManager or NVS-based credential storage for production builds.