Sensing & Perception - Lab 1 & 2 Arduino final codes repository

Arduino Weight Sensor Scale with Servo Pointer

This repository contains two Arduino sketches designed to estimate mass using different types of force/weight sensors and display the result both digitally (via the serial monitor) and analogically (using a servo motor as a pointer).

Repository Contents

• Interpolation_Gauge_Strain_Load_Cells_Estimation.ino: Arduino sketch for estimating mass using a strain gauge load cell. It assumes the input signal (voltage) has been amplified, adjusted, and scaled to a range of [0-5]V.
• Interpolation_FlexiForce_Estimation.ino: Arduino sketch for estimating mass using a FlexiForce A201 sensor. It also assumes the input signal (voltage) is within the range of [0-5]V.

Overview

Both sketches implement a similar approach to estimate mass:

1. Analog Input Reading: They read the analog voltage from a specified sensor pin (A0).
2. Voltage Conversion: The raw analog reading (0-1023) is converted to a voltage value (0-5V).
3. Mass Estimation via Linear Interpolation: They use a pre-defined calibrationData array to map the measured voltage to an estimated mass in grams using linear interpolation. This allows for non-linear sensor responses to be approximated.
4. Digital Output: The raw sensor value, voltage, and estimated mass are printed to the Arduino Serial Monitor.
5. Analog Output via Servo: The estimated mass is then mapped to an angle (0-180 degrees) to control a servo motor, which acts as a pointer on a scale.

Hardware Requirements

• Arduino board
• Force/Weight sensor (Strain Gauge Load Cell or FlexiForce A201, depending on the sketch)
• Signal conditioning circuitry for the sensor (amplifier, offset adjustment, scaling) to provide a 0-5V output range corresponding to the sensor's measurement range.
• Servo motor
• Connecting wires

Software Requirements

• Arduino IDE (Tested : Version 2.1.4) installed.

Setup

1. Connect the Sensor: Connect the output of your sensor's signal conditioning circuit to the Arduino's analog input pin A0.
2. Connect the Servo Motor: Connect the control pin of the servo motor to digital pin 9 on the Arduino. Connect the servo's power and ground pins appropriately (typically to the Arduino's 5V and GND, or an external power supply if needed).
3. Calibration:
   • The sensor needs calibration. This involves applying known weights to the sensor and recording the corresponding voltage readings from the Arduino (via the Serial Monitor, or via an external multimeter).
   • Edit the calibrationData array in the chosen sketch with your collected voltage and mass pairs. Ensure the data is sorted in ascending order of voltage. The comments in the code provide guidance on the format.
   • Test the full range of your sensor to get accurate estimations. Masses outside the tested range might not yield reliable results.
4. Upload the Sketch: Open the desired .ino file in the Arduino IDE, select your Arduino board and port, and upload the sketch to your Arduino.
5. Open Serial Monitor: Open the Serial Monitor in the Arduino IDE (Tools > Serial Monitor) to see the digital output of the estimated mass and servo angle.

Usage

Once the sketch is uploaded and the hardware is connected, placing weight on the sensor will:

• Display the raw sensor reading, voltage, and estimated mass in grams on the Serial Monitor.
• Move the servo motor's arm to an angle proportional to the estimated mass, acting as a pointer on a scale.

Code Explanation

Interpolation_Gauge_Strain_Load_Cells_Estimation.ino and Interpolation_FlexiForce_Estimation.ino

Both sketches share a similar structure and functionality, with the main difference being the calibrationData tailored to the specific sensor characteristics, since the input nature and range is the same (a voltage of range 0 to 5V).

• #include <Servo.h>: Includes the Servo library for controlling the servo motor.
• Servo myServo;: Creates a Servo object.
• const int sensorPin = A0;: Defines the analog input pin for the sensor.
• const int servoPin = 9;: Defines the digital pin for the servo motor.
• double calibrationData[][2]: A 2D array storing the calibration points. Each inner array contains a voltage value (in Volts) and the corresponding mass (in grams). This array must contain your calibration data in ascending order of voltage.
• const int calibrationDataSize: Calculates the number of calibration points in the calibrationData array.
• double getVoltage(int rawValue): Converts the raw analog reading (0-1023) to a voltage (0-5V).
• double getMass(double voltage): This function performs linear interpolation to estimate the mass based on the measured voltage and the calibrationData.
  • It handles cases where the input voltage is outside the calibrated range by returning the mass at the closest calibration point.
  • It iterates through the calibrationData to find the voltage interval where the current voltage falls and then performs linear interpolation to estimate the corresponding mass.
  • It returns -1 if there's an issue (which should not occur if the calibrationData is sorted correctly).
• int massToAngle(double mass): This function maps the estimated mass (currently assumed to be within a 0-500g range, but you should adjust this based on your calibration) to a servo angle between 0 and 180 degrees. You will likely need to adjust the map() function's input range (0 and 500) to match the actual minimum and maximum mass values in your calibrationData once you have data for your full measurement range. However, nothing prevents from limiting the output while still having the calibration points.
• void setup(): Initializes serial communication and attaches the servo object to the servo pin.
• void loop():
  • Reads the raw analog value from the sensor.
  • Converts the raw value to voltage using getVoltage().
  • Estimates the mass using getMass().
  • Prints the raw value, voltage, and estimated mass to the Serial Monitor.
  • If a valid mass is estimated, it converts the mass to a servo angle using massToAngle(), constrains the angle within the servo's limits (0-180), and writes the angle to the servo motor.
  • Prints the calculated servo angle to the Serial Monitor.
  • Includes a small delay.

Notes

• Calibration is critical for accurate mass estimation. Spend time to collect good calibration data that covers the expected range of your measurements.
• The linear interpolation provides an approximation of the sensor's response. For highly non-linear sensors, more calibration points will generally lead to better accuracy.
• The massToAngle() function currently maps a 0-500g range to the servo's 0-180-degree range. You will need to adjust the input range of the map() function in massToAngle() to reflect the actual minimum and maximum mass values you have in your calibrationData to utilize the full range of your sensor and the servo. For example, if your calibration data spans 0g to 800g, you should change map(mass, 0, 500, 0, 180) to map(mass, 0, 800, 0, 180).
• Consider adding error handling or visual indicators (e.g., servo moving beyond a certain range) for masses outside the calibrated range.

Author

Charles STELANDRE

Version

V0.1

Date

2025/05/11