Pressure Sensor

The pressure sensors are analog force sensing resistor (FSR) pads read via ADC, intended primarily for robotic gripper force feedback: grip force sensing, object presence detection, and load distribution across two gripper pads. The system supports a dual sensor configuration. 
 Hardware Specifications 
 Parameter Value Sensor Count 2 (independent) Interface Analog ADC (compile gated, see Hardware Status below) Board pins PD15 (FORCE_ANALOG_DATA_1), PF3 (FORCE_ANALOG_DATA_2) Output unit kPa 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: 
 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. Build with -D PRESSURE_USE_ADC . 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;
 float temperature_c;
 float voltage;
 bool is_calibrated;
 bool read_ok; /* true if the last poll read succeeded */

 /* ADC binding (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];
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 pr_result = poll_pressure_sensor(&pressure_data[i]); 
 Data Access Functions 
 float kpa, temp_c, voltage;
bool valid;

pressure_sensor_get_pressure_kpa(&sensor, &kpa);
pressure_sensor_get_temperature_c(&sensor, &temp_c);
pressure_sensor_get_voltage(&sensor, &voltage);
pressure_sensor_is_valid(&sensor, &valid); 
 Calibration 
 /* kPa = V × scale + offset; marks the sensor calibrated */
pressure_sensor_set_calibration(&sensor, scale_kpa_per_volt, offset_kpa); 
 Pressure Unit Conversions 
 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 
 Function-based conversions (bar_to_psi, psi_to_bar) are declared in the utility library but currently commented out; see Sensor Board Utility 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; /* NO_ERROR, COMMUNICATION_FAILURE, INVALID_DATA */
} 
 Applications 
 Robotic Gripper Control (Primary Use Case) 
 Grip force feedback for object handling Object presence detection (pressure spike threshold) Adaptive compliance for varying object sizes and materials Dual sensors support load sharing across gripper pads 
 Possible Secondary Uses (not implemented) 
 Depth sensing (water), altitude sensing (air), system pressure monitoring, if a suitable transducer replaces the FSR pads 
 Integration Notes 
 Two independent units polled every main loop iteration, each transmitted in its own envelope with its sensor_index (logged under the name "Force0"/"Force1") Each sensor maintains independent calibration and error reporting The temperature_c field exists for future compensation algorithms; no temperature source is wired up yet Until the ADC is enabled the sensors are harmless placeholders: IDLE / DISCONNECTED, zeroed values