Python • Pi 5 with SparkFun Load Cell Amp

Code:

#!/usr/bin/env python3"""Raspberry Pi 5 HX711 Load Cell TestThis Python script tests the HX711 and load cell on Raspberry Pi 5Wiring:HX711 VDD → RPi 5V (Pin 2 or 4)HX711 VCC → RPi 5V (same as VDD) HX711 GND → RPi GND (Pin 6, 9, 14, 20, 25, 30, 34, or 39)HX711 DT  → RPi GPIO 20 (Pin 38)HX711 SCK → RPi GPIO 21 (Pin 40)Load Cell to HX711:Red   → RED (E+)Black → BLK (E-)  White → WHT (A+)Green → GRN (A-)Installation requirements (Pi 5):sudo apt updatesudo apt install python3-libgpiod"""import gpiodimport timeimport sys# Pin definitions (using GPIO numbers)HX711_DT_PIN = 20    # Data pin (Physical Pin 38)HX711_SCK_PIN = 21   # Clock pin (Physical Pin 40)# Calibration - set this to your baseline readingZERO_VALUE = -155456  # Your baseline/tare valueclass HX711:    def __init__(self, dt_pin, sck_pin):        self.dt_pin = dt_pin        self.sck_pin = sck_pin        self.chip = gpiod.Chip('gpiochip0')                 # Request GPIO lines        self.dt_line = self.chip.get_line(self.dt_pin)        self.sck_line = self.chip.get_line(self.sck_pin)                # Configure pins        self.dt_line.request(consumer="HX711_DT", type=gpiod.LINE_REQ_DIR_IN)        self.sck_line.request(consumer="HX711_SCK", type=gpiod.LINE_REQ_DIR_OUT)                # Set SCK low initially        self.sck_line.set_value(0)        def cleanup(self):        """Clean up GPIO resources"""        try:            self.dt_line.release()            self.sck_line.release()            self.chip.close()        except:            pass        def reset(self):        """Reset the HX711 by sending 25+ clock pulses"""        print("Resetting HX711...")        for _ in range(30):            self.sck_line.set_value(1)            time.sleep(0.000001)  # 1 microsecond            self.sck_line.set_value(0)            time.sleep(0.000001)        time.sleep(0.1)        def is_ready(self):        """Check if HX711 is ready (DT is low)"""        return self.dt_line.get_value() == 0        def read_raw(self):        """Read raw value from HX711"""        # Wait for HX711 to be ready (DT goes low)        timeout = time.time() + 1.0  # 1 second timeout        while self.dt_line.get_value() == 1 and time.time() < timeout:            time.sleep(0.00001)  # 10 microseconds                if time.time() >= timeout:            print("Timeout waiting for HX711")            return 0                # Read 24 bits        value = 0        for i in range(24):            self.sck_line.set_value(1)            time.sleep(0.000001)  # 1 microsecond                        value = (value << 1) | self.dt_line.get_value()                        self.sck_line.set_value(0)            time.sleep(0.000001)                # Send one more pulse to set gain to 128 for next reading        self.sck_line.set_value(1)        time.sleep(0.000001)        self.sck_line.set_value(0)        time.sleep(0.000001)                # Convert from 24-bit unsigned to signed        if value & 0x800000:            value |= 0xFF000000  # Sign extend for 32-bit signed            # Convert to proper signed 32-bit integer            value = value - 2**32 if value >= 2**31 else value                return value        def print_diagnostics(self):        """Print diagnostic information"""        print("\n=== HX711 Diagnostics ===")                # Check pin states        dt_state = "HIGH" if self.dt_line.get_value() else "LOW"        print(f"DT Pin State: {dt_state}")                # Test SCK control        print("Testing SCK control...")        self.sck_line.set_value(1)        time.sleep(0.01)        sck_high = "HIGH" if self.sck_line.get_value() else "LOW"        print(f"SCK set HIGH, reading: {sck_high}")                self.sck_line.set_value(0)        time.sleep(0.01)        sck_low = "HIGH" if self.sck_line.get_value() else "LOW"        print(f"SCK set LOW, reading: {sck_low}")                print()def main():    """Main program loop"""    hx711 = None        try:        print("Raspberry Pi 5 HX711 Load Cell Test")        print("===================================")                # Initialize HX711        hx711 = HX711(HX711_DT_PIN, HX711_SCK_PIN)                print(f"DT Pin: GPIO {HX711_DT_PIN}")        print(f"SCK Pin: GPIO {HX711_SCK_PIN}")        print(f"Zero baseline: {ZERO_VALUE}")                # Reset HX711        hx711.reset()                time.sleep(1)                print("Starting readings...")        print("Apply pressure to load cell to test response")        print("Press Ctrl+C to exit")        print()                while True:            # Check if HX711 is ready            if hx711.is_ready():                                # Read raw value                raw_value = hx711.read_raw()                                # Calculate zeroed value                zeroed_value = raw_value - ZERO_VALUE                                # Print results                print(f"Raw: {raw_value} → Zeroed: {zeroed_value}", end="")                                # Status indicators                if raw_value == -1:                    print(" ⚠️  All bits high - check A+/A- wiring")                elif raw_value == 0:                    print(" ⚠️  All bits low - check connections")                elif abs(zeroed_value) < 100:                    print(" ✅ At rest")                elif zeroed_value > 100:                    print(" 📈 Positive pressure")                elif zeroed_value < -100:                    print(" 📉 Negative pressure")                else:                    print()                            else:                print("HX711 not ready (DT high) - check power and connections")                        time.sleep(0.5)  # Read every 500ms                except KeyboardInterrupt:        print("\nExiting...")    except Exception as e:        print(f"Error: {e}")        print("Make sure you have installed: sudo apt install python3-libgpiod")        print("And that you're running as root: sudo python3 hx711_test.py")    finally:        if hx711:            hx711.cleanup()if __name__ == "__main__":    main()