In this DIY electronics project, we will design and build a precision weighing scale using the AD7799BRUZ, a high-precision analog-to-digital converter (ADC) from Analog Devices. This project involves using the AD7799BRUZ in conjunction with a load cell to measure the weight of an object and display the result on a digital display, such as an LED or LCD screen. The AD7799BRUZ offers a high level of precision and noise immunity, making it ideal for applications requiring accurate measurements, such as in weighing scales, force measurement systems, and industrial sensors.

The project will consist of several key components, including the AD7799BRUZ ADC, a load cell to measure weight, a microcontroller (e.g., Arduino) to process the data, and a display to show the weight readings. We will also implement a calibration mechanism to ensure that the system can accurately measure weight based on known reference weights.

The AD7799BRUZ provides 24-bit resolution, which ensures that even very small changes in weight are accurately detected. Its integrated features like programmable gain amplifiers (PGAs), differential inputs, and low noise operation make it a perfect fit for this type of project.

Components Needed

For this DIY precision weighing scale project, we will need the following components:

· AD7799BRUZ Precision ADC (1 piece)

· Load Cell (e.g., 5kg or 10kg capacity)

· HX711 or similar amplifier IC for load cell signal amplification

· Microcontroller (e.g., Arduino, STM32, or any other suitable microcontroller)

· LCD Display or LED 7-Segment Display to show the weight

· Resistors:

o 10 kΩ (for voltage divider or pull-up resistors)

o 1 kΩ (for signal conditioning)

· Capacitors:

o 0.1 µF (for noise filtering)

o 10 µF (for power smoothing)

· Voltage Regulator (e.g., LM7805 for 5V power supply)

· Power Supply (5V DC from a battery or adapter)

· Wires, Connectors, and Soldering Tools

· Reference Weight for calibration (e.g., 500g, 1kg, or 5kg)

· Calibration Software (optional for adjusting the weight readings)

Understanding the AD7799BRUZ

The AD7799BRUZ is a 24-bit delta-sigma ADC designed for high-precision measurements in industrial, medical, and scientific applications. Its key features include:

· 24-bit resolution: Provides high precision for measurements with low noise.

· Low noise operation: It offers excellent noise rejection and stability, which is essential in weighing scales where small changes in weight must be detected.

· Integrated programmable gain amplifier (PGA): This allows it to work with low-voltage sensors like load cells and amplify weak signals.

· Differential input: Ideal for measuring the difference in voltage across two points, such as the output of a load cell.

· Low power consumption: It operates efficiently in battery-powered applications.

· Flexible interface: It communicates using I2C or SPI, making it compatible with a variety of microcontrollers.

These characteristics make the AD7799BRUZ perfect for this application, where precision and stability are crucial for accurate weight measurements.

Project Overview: Precision Weighing Scale

The goal of this project is to build a digital weighing scale that can accurately measure the weight of objects and display the result on a digital display. The project will use the AD7799BRUZ ADC to convert the analog signal from the load cell into a digital value, which will then be processed by a microcontroller and displayed on an LCD or LED display.

The load cell is a transducer that converts the force (weight) applied to it into a small electrical signal. This signal is usually very weak and needs to be amplified before it can be read by the ADC. The HX711 amplifier IC is commonly used in conjunction with load cells to amplify the signal to a level suitable for the ADC. The AD7799BRUZ will then convert this amplified signal into a digital value, which can be interpreted by the microcontroller to determine the weight.

Circuit Design Overview

The circuit will have the following main sections:

1. Load Cell and Amplifier: The load cell will measure the weight of an object, and its small analog output will be amplified using the HX711 amplifier IC.

2. Analog-to-Digital Conversion: The amplified signal from the load cell will be fed into the AD7799BRUZ, where it will be converted into a high-precision digital value.

3. Microcontroller: The microcontroller will process the digital data from the AD7799BRUZ, convert it into a readable weight value, and display the result on an LCD or LED display.

4. Power Supply: A stable 5V power supply will be provided to the circuit to ensure consistent operation.

Step-by-Step Guide to Building the Precision Weighing Scale

Step 1: Preparing the Load Cell and HX711 Amplifier

Connecting the Load Cell:

o A load cell typically has four wires: Excitation+ (E+), Excitation- (E-), Signal+ (S+), and Signal- (S-). The Excitation+ and Excitation- wires are used to supply power to the load cell, while the Signal+ and Signal- wires carry the output signal corresponding to the applied weight.

o Connect the Excitation+ to the VCC of the HX711 amplifier, and the Excitation- to GND.

o Connect the Signal+ and Signal- from the load cell to the A+ and A- pins of the HX711 amplifier.

Amplifying the Signal:

o The HX711 amplifier is designed to amplify the small signal from the load cell. Connect the DT (Data) and SCK (Clock) pins of the HX711 to the corresponding pins on the microcontroller for data communication.

Step 2: Setting Up the AD7799BRUZ ADC

Powering the AD7799BRUZ:

o Connect the VDD and GND pins of the AD7799BRUZ to a stable 5V power supply and ground, respectively. You may use an LM7805 voltage regulator if you're using a higher voltage power supply.

Connecting the Output of HX711 to AD7799BRUZ:

o The HX711 amplifies the signal from the load cell, and the amplified signal can now be fed into the AD7799BRUZ via its AIN+ and AIN- differential input pins.

o Ensure that the signal is within the input range of the AD7799BRUZ for accurate measurements.

Configuration of AD7799BRUZ:

o Use the SPI or I2C interface to communicate with the AD7799BRUZ. Configure the device to read the differential input and set the gain (if necessary) for optimal signal conditioning.

Step 3: Processing Data with the Microcontroller

Microcontroller Interface:

o Connect the SCK, SDI (Serial Data In), and CS (Chip Select) pins of the AD7799BRUZ to the corresponding pins on the microcontroller (such as an Arduino or STM32).

o The microcontroller will send commands to the AD7799BRUZ to initiate conversions and retrieve the digital weight data.

Signal Processing:

o The microcontroller will read the digital data from the AD7799BRUZ, process it to calculate the weight (taking into account any calibration data), and then convert the digital value into a weight reading.

Step 4: Displaying the Weight on an LCD

LCD/LED Display:

o Connect a 16x2 LCD or 7-segment LED display to the microcontroller to display the weight reading.

o The microcontroller will send the weight value to the display, which will show the weight in grams or kilograms depending on your calibration.Step 5: Calibration

Calibrating the Weighing Scale:

o Calibration is a critical step in ensuring that the scale gives accurate measurements.

o Start by applying a known reference weight (e.g., 1kg) to the load cell and adjust the microcontroller’s software to match the display output to the known weight.

o You can also implement a two-point or multi-point calibration by using different reference weights and adjusting the scaling factor in the code.

Step 6: Testing and Adjustment

Testing the Weighing Scale:

o After calibration, test the scale with different objects to check the accuracy of the measurements.

o Adjust the gain of the AD7799BRUZ and the HX711 amplifier if needed to ensure accurate readings across the weight range.

Fine-Tuning:

o If the scale is slightly off, you can adjust the software to account for small discrepancies or recalibrate with more reference weights.

Conclusion

In this DIY project, we successfully built a precision weighing scale using the AD7799BRUZ ADC, HX711 amplifier, and a load cell. The combination of these components enabled us to create an accurate and reliable digital weighing system with high resolution and low noise, which is essential for measuring even small changes in weight. By utilizing the 24-bit resolution of the AD7799BRUZ and the amplification capabilities of the HX711, we achieved precise weight measurements that can be displayed clearly on an LCD or LED screen.

The project demonstrated the power of integrating high-precision ADCs, such as the AD7799BRUZ, into real-world applications. This component's ability to handle low-voltage, noisy signals and deliver accurate digital outputs made it an excellent choice for this project. Additionally, the calibration process, although crucial, was simple to implement, ensuring that the scale provided consistent and reliable readings.

The resulting digital weighing scale can be used in various applications, from basic DIY projects to more advanced uses in industrial and scientific fields where precise weight measurement is required. This project is a great example of how accessible high-performance electronics are for hobbyists and engineers alike, and it serves as a strong foundation for building more complex sensor-based systems in the future.

With the knowledge gained from this project, you can further improve and refine the scale, adjust the software for different weight ranges, or even explore additional features like tare functions, data logging, or wireless communication. Ultimately, this weighing scale is a perfect blend of accuracy, affordability, and functionality, making it a valuable addition to any electronics enthusiast's toolkit.