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hx710b.py

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+from machine import Pin
+import time
+import json
+import os
+
+CALIB_FILE = "calibration.cfg"
+
+
+# ---------------------------------------------------------
+# Calibration File Helpers
+# ---------------------------------------------------------
+
+def save_calibration(zero_offset, scale_factor):
+    """Save calibration values to internal flash."""
+    data = {
+        "zero_offset": zero_offset,
+        "scale_factor": scale_factor
+    }
+    with open(CALIB_FILE, "w") as f:
+        json.dump(data, f)
+    print("✔ Calibration saved.")
+
+
+def load_calibration():
+    """Load existing calibration or return defaults."""
+    if CALIB_FILE not in os.listdir():
+        print("⚠ No calibration file found, using defaults.")
+        return 0, 1
+
+    try:
+        with open(CALIB_FILE, "r") as f:
+            data = json.load(f)
+        print("✔ Calibration loaded.")
+        return data.get("zero_offset", 0), data.get("scale_factor", 1)
+    except Exception as e:
+        print("⚠ Calibration load error:", e)
+        return 0, 1
+
+
+# ---------------------------------------------------------
+# HX710B Class
+# ---------------------------------------------------------
+
+class HX710B:
+    def __init__(self, dout_pin, sck_pin):
+        self.dout = Pin(dout_pin, Pin.IN)
+        self.sck = Pin(sck_pin, Pin.OUT)
+        self.sck.value(0)
+
+        # Load previous calibration (or defaults)
+        self.zero_offset, self.scale_factor = load_calibration()
+
+    # -----------------------------------------------------
+    # Low-level raw ADC read
+    # -----------------------------------------------------
+    def read_raw(self):
+        """Read the 24-bit raw ADC value."""
+        while self.dout.value():
+            pass  # wait for data ready
+
+        count = 0
+        for _ in range(24):
+            self.sck.value(1)
+            count = (count << 1) | self.dout.value()
+            self.sck.value(0)
+
+        # 25th pulse to set gain for next reading
+        self.sck.value(1)
+        self.sck.value(0)
+
+        # Signed 24-bit conversion
+        if count & 0x800000:
+            count -= 0x1000000
+
+        return count
+
+    # -----------------------------------------------------
+    # Zero Calibration
+    # -----------------------------------------------------
+    def calibrate_zero(self, samples=20):
+        """Measure 0 kPa and determine zero offset."""
+        total = 0
+        for _ in range(samples):
+            total += self.read_raw()
+            time.sleep_ms(5)
+
+        self.zero_offset = total / samples
+        save_calibration(self.zero_offset, self.scale_factor)
+
+        print("✔ Zero calibrated:", self.zero_offset)
+        return self.zero_offset
+
+    # -----------------------------------------------------
+    # Full-scale / Known Pressure Calibration
+    # -----------------------------------------------------
+    def calibrate_full(self, known_kpa, samples=20):
+        """Measure raw ADC at known pressure and compute scaling."""
+        total = 0
+        for _ in range(samples):
+            total += self.read_raw()
+            time.sleep_ms(5)
+
+        raw_avg = total / samples
+        self.scale_factor = known_kpa / (raw_avg - self.zero_offset)
+
+        save_calibration(self.zero_offset, self.scale_factor)
+
+        print("✔ Scale calibrated:", self.scale_factor)
+        return self.scale_factor
+
+    # -----------------------------------------------------
+    # Convert raw → kPa using saved calibration
+    # -----------------------------------------------------
+    def read_kpa(self):
+        raw = self.read_raw()
+        return (raw - self.zero_offset) * self.scale_factor