CW32 Voltage and Current Meter

I. Project Introduction
 An ADC (Analog-to-Digital Converter) is an indispensable key component in electronic systems. It converts continuous analog signals into digital signals, enabling digital processing and analysis. ADCs play a crucial role in signal conversion, measurement and data acquisition, control system input, and communication and signal processing. Their widespread application promotes the intelligent and precise control of electronic equipment across various industries, and is one of the key factors driving modern technological progress.
  Digital voltmeters and ammeters combine ADC technology with circuit measurement principles, accurately converting analog voltage and current signals into digital displays for easy reading and analysis by electronic engineers. This device not only improves the accuracy and efficiency of circuit measurements but also helps engineers better understand circuit behavior, making it a powerful tool for electronic design and troubleshooting, and playing a vital supporting role in the work of electronic engineers. In product applications, digital voltmeters ensure the accuracy and safety of circuit design, while also providing strong support for product quality control and subsequent maintenance.
II. Principle Analysis (Hardware Description)
1. Power Supply Circuit
LDO (Low Dropout Linear Regulator) Selection
This project uses an LDO as the power supply. Considering that most voltmeter products are used in industrial scenarios with 24V or 36V power supplies, the SE8550K2 with a maximum input voltage of up to 40V was selected as the power supply. The main reason for not using a DC-DC step-down circuit to handle the large voltage drop is to avoid introducing DC-DC ripple interference during the design process; a secondary reason is to reduce project costs.
2. Voltage Sampling Circuit
The voltage divider resistors in this project are designed to be 220K+10K, so the voltage division ratio is 22:1 (ADC_IN11).
Voltage divider resistor selection
(1) The maximum value of the designed measurement voltage. For safety reasons, this project is 30V (the actual maximum can be displayed as 99.9V or 100V);
(2) ADC reference voltage. In this project, it is 1.5V. This reference voltage can be configured through the program;
(3) Power consumption. In order to reduce the power consumption of the sampling circuit, the low-side resistor (R7) is usually selected as 10K based on experience; 3.
Current Sampling Circuit
This project uses a low-side current sampling circuit for current detection. The sampling current designed for the low side of the sampling circuit and the development board meter interface
is 3A. The selected sampling resistor (R0) is 100mΩ.
The sampling selection mainly needs to consider the following aspects:
(1) The maximum value of the pre-designed measurement current. In this project, it is 3A
; (2) The voltage difference caused by the current sensing resistor. It is generally not recommended to exceed 0.5V.
(3) The power consumption of the current sensing resistor should be selected according to the appropriate package. Considering the power consumption (temperature) problem under high current, a 1W packaged metal wire-wound resistor was selected in this project.
(4) The amplification factor of the voltage across the current sensing resistor: No operational amplifier was used to build the amplifier circuit in this project, so the amplification factor is 1.
III. Precautions
: Do not solder R0 during testing!