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:

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;
  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