Pressure Sensor

PressureThe pressure sensors measureare fluid/gasanalog pressureforce sensing resistor (FSR) pads read via ADC, intended primarily for robotic gripper force feedbackfeedback: grip force sensing, object presence detection, and control,load depthdistribution sensing,across altitudetwo measurement,gripper or system pressure monitoring.pads. The system supports a dual pressure sensor configuration for dual-pad gripper control with load distribution feedback.configuration.

Hardware Specifications

Parameter	Value
Sensor Count	2 (independent)
Interface	Analog ADC or(compile I2Cgated, see Hardware Status below)
MeasurementBoard Rangepins	VariablePD15 (typicallyFORCE_ANALOG_DATA_1), 0-300PF3 kPa)(FORCE_ANALOG_DATA_2)
UpdateOutput Rateunit	ConfigurablekPa via linear conversion, plus raw voltage and temperature field

Hardware Status

The ADC path is compile gated by PRESSURE_USE_ADC because no ADC is enabled in CubeMX yet. Without the flag, poll_pressure_sensor() returns RESULT_ERR_UNIMPLEMENTED and both sensors report IDLE / DISCONNECTED (the firmware still links). To enable:

1. In CubeMX enable an ADC and the channel(s) for the force pins. On the STM32H753, PD15 has NO ADC function and PF3 = ADC3_INP5, so FORCE_ANALOG_DATA_1 must be moved to an ADC-capable pin.
2. Build with -D PRESSURE_USE_ADC.
3. Bind each unit with pressure_sensor_init_hw().

Conversion Model

voltage      = raw / adc_max × reference_voltage
pressure_kpa = voltage × scale_kpa_per_volt + offset_kpa

Defaults: scale_kpa_per_volt = 1.0, offset_kpa = 0.0 (passthrough until calibrated).

Data Structure

typedef struct {
  float pressure_kpa;
  // Pressure in kilopascals (kPa)
    float temperature_c;        // Temperature in Celsius (°C)
  float voltage;
  // Sensor output voltage
    bool is_calibrated;
  bool read_ok;              /* true if the last poll read succeeded */

  Calibration/* statusADC flagbinding (set by pressure_sensor_init_hw) */
  void *adc_handle;          /* ADC_HandleTypeDef* (void* keeps header HAL-free) */
  uint32_t adc_channel;      /* ADC_CHANNEL_x */
  uint32_t adc_max;          /* full-scale count (e.g. 65535 for 16-bit) */
  float reference_voltage;   /* ADC Vref+ in volts */
  float scale_kpa_per_volt;  /* linear gain (default 1.0) */
  float offset_kpa;          /* linear offset (default 0.0) */
} pressure_sensor_data_t;

Initialization

Initialize Pressure Sensors (as in main.c)

pressure_sensor_data_t pressure_data[2];  // Support 2 sensors
for (size_t i = 0; i < 2; i++) {
    pressure_sensor_init(&pressure_data[i]);
}

/* Once an ADC exists, bind it per unit: */
pressure_sensor_init_hw(&pressure_data[1], &hadc3, ADC_CHANNEL_5,
                        65535U, 3.3f);

Poll Pressure Sensor

result_t ps_resultpr_result = poll_pressure_sensor(&pressure_data[0]i]);

if (ps_result == RESULT_OK) {
    float pressure_kpa = pressure_data[0].pressure_kpa;
    float temperature_c = pressure_data[0].temperature_c;
}

Data Access Functions

//float Getkpa, pressuretemp_c, involtage;
kilopascalsbool result_tvalid;

pressure_sensor_get_pressure_kpa(&sensor, const pressure_sensor_data_t *data,
    float *pressure_kpa
)&kpa);
//pressure_sensor_get_temperature_c(&sensor, Get temperature in Celsius
result_t pressure_sensor_get_temperature_c(
    const pressure_sensor_data_t *data,
    float *temperature_c
)&temp_c);
pressure_sensor_get_voltage(&sensor, &voltage);
pressure_sensor_is_valid(&sensor, &valid);

Calibration

//* GetkPa raw= V × scale + offset; marks the sensor voltage
result_t pressure_sensor_get_voltage(
    const pressure_sensor_data_tcalibrated *data,
    float *voltage
);

//
Verifypressure_sensor_set_calibration(&sensor, sensorscale_kpa_per_volt, validity
result_t pressure_sensor_is_valid(
    const pressure_sensor_data_t *data,
    bool *is_valid
)offset_kpa);

Pressure Unit Conversions

Function-Based Conversions

// Convert pressure from bar to psi
result_t bar_to_psi(float bar, float *psi);

// Convert pressure from psi to bar
result_t psi_to_bar(float psi, float *bar);

Conversion Table

From	To	Multiply By
bar	kPa	100
psi	kPa	6.895
atm	kPa	101.325
kPa	bar	0.01
kPa	psi	0.145
kPa	atm	0.00987

Examples

Function-based

// 100 kPa = 1 bar
float kpa = 100.0f;
float bar = kpa * 0.01f;  // Result: 1.0 bar

// 50 psi to bar
float psi = 50.0f;
float bar = psi / 14.504f;  // Result: 3.45 bar

// Altitude from pressureconversions (simplified)bar_to_psi, //psi_to_bar) Altitudeare ≈declared 44330in ×the (1utility -library (P/P0)^(1/5.255))but floatcurrently altitude_mcommented =out; 44330.0fsee *Sensor (1.0fBoard -Utility pow(pressure_kpa/101.325f, 1.0f/5.255f));

Library.

Protobuf Message Format

message SensorBoardPressureInfo {
    uint32 sensor_index;            //* 0 or 1 */
    float pressure_kpa;
    float temperature_c;
    float voltage;
    bool is_calibrated;
    SensorState state;
    PressureErrorCode error_code;   }

/*

DualNO_ERROR, SensorCOMMUNICATION_FAILURE, Management

INVALID_DATA

Configuration Example

/*/
Initialize both sensors
for (size_t i = 0; i < 2; i++) {
    pressure_sensor_init(&pressure_data[i]);
}

// Poll both in sequence
poll_pressure_sensor(&pressure_data[0]);
poll_pressure_sensor(&pressure_data[1]);

// Access by index
float pressure_0_kpa = pressure_data[0].pressure_kpa;
float pressure_1_kpa = pressure_data[1].pressure_kpa;

Temperature Compensation

Pressure readings often need temperature compensation for accuracy:

// Simplified temperature compensation
float compensated_pressure = pressure_data[0].pressure_kpa * 
    (reference_temperature + 273.15f) / 
    (pressure_data[0].temperature_c + 273.15f);

Applications

Robotic Gripper Control (Primary Use Case)

// Gripper force feedback for adaptive grip strength
// Pressure reading controls servo/motor PWM to regulate grip force

#define GRIPPER_MIN_PRESSURE_KPA 20.0f   // Minimum safe grip
#define GRIPPER_MAX_PRESSURE_KPA 150.0f  // Maximum allowed grip
#define GRIPPER_TARGET_PRESSURE_KPA 80.0f // Desired grip force

// PID controller for gripper force regulation
typedef struct {
    float kp, ki, kd;            // PID coefficients
    float integral_error;
    float previous_error;
} gripper_pid_t;

// Adjust servo PWM based on pressure feedback
void adjust_gripper_force(float current_pressure_kpa, gripper_pid_t *pid) {
    float error = GRIPPER_TARGET_PRESSURE_KPA - current_pressure_kpa;
    
    pid->integral_error += error;
    float derivative_error = error - pid->previous_error;
    
    float pid_output = (pid->kp * error) + 
                       (pid->ki * pid->integral_error) + 
                       (pid->kd * derivative_error);
    
    // Clamp servo PWM to valid range
    uint16_t servo_pwm = (uint16_t)(GRIPPER_NEUTRAL_PWM + pid_output);
    servo_pwm = (servo_pwm < GRIPPER_MIN_PWM) ? GRIPPER_MIN_PWM : servo_pwm;
    servo_pwm = (servo_pwm > GRIPPER_MAX_PWM) ? GRIPPER_MAX_PWM : servo_pwm;
    
    set_gripper_pwm(servo_pwm);
    pid->previous_error = error;
}

Gripper Control Features:

• Grip force feedback for object handling
• Object presence detection (pressure spike threshold)
• Adaptive compliance for varying object sizes/sizes and materials
• Dual sensors support load sharing across gripper pads

ImplementedPossible butSecondary NotUses Primary(not implemented)

• Depth Sensingsensing (Water)

water),

//altitude Pressure to depth in water
// P = ρ × g × h
// where ρ = 1025 kg/m³sensing (seawater)air), g = 9.81 m/s²
float depth_meters = (pressure_kpa - atmospheric_pressure_kpa) / 10.0f;

Altitude Sensing (Air)

// Barometric formula (simplified)
float altitude_m = 44330.0f * (1.0f - pow(pressure_kpa/101.325f, 1.0f/5.255f));

System Pressure Monitoring

if (pressure_kpa > PRESSURE_WARNING_THRESHOLD) {
    // Highsystem pressure detectedmonitoring, -if safetya alert
}

Common Pressure Sensor Ranges

Application	Range	Typical Sensor
Altitude (aviation)	10-110 kPa	BMP280/BMP390
Depth (diving)	0-300+ kPa	Custom depth sensor
System pressure	0-500+ kPa	Industrial pressuresuitable transducer

 replaces the FSR pads

Integration Notes

• Primary Application: Robotic gripper force feedback and control
• Supports up to 2Two independent pressureunits sensorspolled (dualevery gripper pads)
• Temperature measurement for compensation algorithms
• Hardware-specific ADC or I2C implementation
• Pressure-voltage conversion implemented internally
• Real-time depth/altitude sensing capability
• PID controlmain loop integrationiteration, foreach adaptivetransmitted gripin forceits own envelope with its sensor_index (logged under the name "Force0"/"Force1")
• Each sensor maintains independent calibration and error reporting
• TemperatureThe trackingtemperature_c field exists for accuracyfuture improvementscompensation algorithms; no temperature source is wired up yet
• SlipUntil detectionthe viaADC pressureis varianceenabled analysisthe sensors are harmless placeholders: IDLE / DISCONNECTED, zeroed values