DMS load cell with measuring amplifier HX711AD
| Autor: | Onyesi John Abiagam |
| Sprache: | DE EN |
Introduction
A weighing scale is a measurement system used to determine the mass of an object by converting mechanical force into a readable value.
This system is based on a DMS load cell in combination with the HX711AD measuring amplifier. The applied force is converted into an electrical signal, which is processed and displayed as a weight value.
The signal is acquired using a microcontroller-based system and processed using Simulink. Calibration, signal filtering, stability detection, and tare functionality are implemented to ensure accurate and stable measurements.
Requirements
| Req. | Description | Priority |
|---|---|---|
| 1 | The mass must be determined using the HX711AD load cell via Arduino and Simulink. | 1 |
| 2 | The measuring range must be determined. | 1 |
| 3 | The measurement uncertainty (1σ) must be determined for the measuring range and displayed as a confidence interval. | 2 |
| 4 | The on/off button starts the system. The sensor must first be calibrated and display 0 g. |
1 |
| 5 | The weight must be referenced for the measuring range. | 1 |
| 6 | The measured values must be filtered/smoothed over time. | 1 |
| 7 | A beep must indicate when the measured value is stable/constant. | 1 |
| 8 | The sensor system must display the weight in g on a display. | 1 |
| 9 | The tara button resets the current weight to 0 g (recalibration). |
1 |
Working principle
This section explains how the DMS load cell and the HX711AD convert an applied force into a digital signal.
DMS Load Cell
Introduction
A DMS load cell converts mechanical force into an electrical signal. It consists of:
- a deformable metal body
- strain gauges attached to the surface
- resistance changes when stretched or compressed
Working Principle
When force is applied:
- the metal body deforms
- strain gauges change resistance
- gauges are wired in a Wheatstone bridge
- deformation → bridge becomes unbalanced
- output: small differential voltage
---
HX711AD Measuring Amplifier
Introduction
The HX711AD processes the small differential signal from the load cell. It includes:
- a programmable gain amplifier (PGA)
- a 24‑bit sigma‑delta ADC
Working Principle
Signal processing steps:
- load cell outputs a millivolt‑level differential signal (A+, A−)
- PGA amplifies the signal
- 24‑bit ADC converts it to digital
- microcontroller reads data via:
- DOUT (data)
- SCK (clock)
Technical Overview
Pin Assignment
3.1 Pin Assignment
This section describes the electrical connections between the load cell, the HX711AD,the buzzer,LCD and push buttons and the microcontroller.
Load Cell to HX711
| Load Cell Wire | Function | HX711 Pin | Description |
|---|---|---|---|
| Red | Excitation + (E+) | E+ | Supplies voltage to the bridge |
| Black | Excitation − (E−) | E− | Ground reference |
| White | Signal + (S+) | A+ | Positive input signal |
| Green | Signal − (S−) | A− | Negative input signal |
| Yellow (optional) | Shield | GND | EMI protection |
HX711 to Microcontroller
| HX711 Pin | Function | Microcontroller Pin | Description |
|---|---|---|---|
| VCC | Power Supply | 5V / 3.3V | Power input |
| GND | Ground | GND | Common reference |
| DOUT | Data Output | Digital Input | Sends measurement data |
| PD_SCK | Clock Input | Digital Output | Controls data read |
Microcontroller Peripherals
| Component | Function | Microcontroller Pin | Description |
|---|---|---|---|
| LCD | Display output | I2C (SDA/SCL) | Displays measured weight |
| Buzzer | Acoustic feedback | Digital Output | Indicates stable measurement |
| Push Button (Power) | System control | Interrupt Pin (e.g., D2) | Starts or stops the system |
| Push Button (Tare) | Reset function | Interrupt Pin (e.g., D3) | Resets measured value to 0 g |
Measurement method
Measuring Circuit
Software
Arduino IDE
Simulink
Measurement
Video
Datasheets
Related Links
SVN-Repository
https://svn.hshl.de/svn/HSHL_Projekte/trunk/Arduino_Sensorsammlung
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