SeaPerchDepthSensor

SeaPerchDepthSensor is a classroom-friendly Arduino library for reading depth from an LPS35HW pressure sensor on an Arduino UNO R4 Minima. It hides the I2C register protocol, zero-depth calibration, data validation, timeouts, and automatic bus recovery behind a small API.

#include <SeaPerchDepthSensor.h>

SeaPerchDepthSensor sensor;

void setup() {
  Serial.begin(115200);
  sensor.begin();
}

void loop() {
  if (!sensor.update()) {
    return;  // No safe new reading yet; recovery happens automatically.
  }

  Serial.println(sensor.depthCm());
}

Supported hardware

• Arduino UNO R4 Minima (primary, hardware-tested target)
• Arduino UNO R4 WiFi and Arduino Nano R4 (same core, compile-tested)
• A 5 V-safe, level-shifting LPS35HW breakout at I2C address 0x5D, such as the Adafruit LPS35HW breakout used by the original project
• Freshwater by default; saltwater conversion is selectable

This first release intentionally targets boards in Arduino's renesas_uno platform because its recovery code depends on that core's bounded Wire timeout behavior. Selecting another architecture produces a compile-time message instead of silently removing the safety guarantees.

Connect the breakout to the UNO R4 Minima's SDA, SCL, power, and ground pins. Follow the breakout manufacturer's voltage instructions. The Adafruit breakout includes a regulator and level shifting, so its Vin can use the UNO's 5 V supply. Use external I2C pull-ups when they are not already present on the sensor board. Keep the bus wiring short and address motor electrical noise with suitable suppression, decoupling, and grounding.

Do not connect a bare LPS35HW chip directly to 5 V power or logic. The bare device is a 1.7-3.6 V part and requires suitable regulation and bidirectional level shifting. The LPS35HW sensor package is water resistant; a breakout PCB, wires, solder joints, and connectors are not automatically waterproof.

On UNO R4 WiFi, use the primary SDA/SCL pins at A4/A5. This release does not manage the separate Qwiic connector's Wire1 bus.

Hardware references:

• Adafruit LPS35HW breakout pinout
• ST LPS35HW datasheet

Install

After the library is accepted into Arduino Library Manager:

1. Open Tools > Manage Libraries... in Arduino IDE.
2. Search for SeaPerchDepthSensor.
3. Select the latest version and click Install.

Before registry acceptance, download a release ZIP from GitHub and use Sketch > Include Library > Add .ZIP Library....

Basic API

SeaPerchDepthSensor sensor;

sensor.begin();                 // Calibrate the current pressure as 0 cm.
sensor.update();                // True only for a new validated reading.
sensor.ready();                 // True when a safe reading is published.
sensor.depthCm();               // Depth relative to startup, positive down.
sensor.pressureHpa();           // Absolute pressure in hPa.
sensor.temperatureC();          // Temperature in degrees Celsius.
sensor.temperatureF();          // Temperature in degrees Fahrenheit.
sensor.faultCount();            // Number of detected runtime sample faults.

Keep the sensor still at the intended zero-depth reference while begin() is running. Startup calibration averages 16 fresh samples. Automatic runtime recovery preserves this software baseline instead of redefining the current depth as zero.

For saltwater:

sensor.begin(nullptr, SeaPerchDepthSensor::Water::Saltwater);

Motorized projects

Define a function that immediately disables the motor, configure the motor pins to a safe state first, then pass that function to begin():

void motorOff() {
  analogWrite(enableMotor, 0);
  digitalWrite(motorIn1, LOW);
  digitalWrite(motorIn2, LOW);
}

void setup() {
  // Configure motor pins, then make them safe before starting the sensor.
  motorOff();
  sensor.begin(motorOff);
}

The library calls this callback before every top-level sensor operation, including fault recovery. When update() returns false, skip all motor control for that loop. Do not use old getter values to drive a vehicle.

The microcontroller pins are high impedance during reset, before any sketch can run. Use a physical pull-down on the motor driver's enable input, appropriate travel limits, and a separate emergency stop for the final vehicle.

Recovery behavior

The library uses:

• a 100 kHz I2C clock and 5 ms transaction timeout;
• checked byte counts and finite/range validation;
• bounded sensor reset and fresh-data waits;
• an open-drain, nine-clock I2C bus-clear sequence;
• fast resume before a full sensor reset;
• a software surface-pressure baseline retained through runtime recovery; and
• no dynamic allocation or unbounded polling loops.

update() performs timed recovery itself. A disconnected or stuck sensor never authorizes motor control, but software cannot repair a physically held clock line, missing power, or severe motor EMI.

The recovery process restarts the global Wire bus. Projects sharing that bus with other I2C devices must revalidate those devices after a recovery.

Examples

In Arduino IDE, open File > Examples > SeaPerchDepthSensor:

• ReadDepth prints validated depth and temperature readings.
• MotorSafetyCallback demonstrates the motor-off safety callback.

Credits and license

The simple student-facing API grew from SeaPerch depth-controller work by Talia Seshasai. The bounded I2C driver and recovery implementation were developed for the Arduino UNO R4 Minima version of that project.

Released under the MIT License. This is a community project and is not an official Arduino, STMicroelectronics, Adafruit, RoboNation, or SeaPerch product.