CW32F030C8T6 Voltage and Current Meter

I. Design Background

This design adopts a core board plus expansion board concept, using plug-in components to simplify learning and deepen exploration.
The core board uses the domestic Wuhan Xinyuan Semiconductor CW32 as the main controller, while also being compatible with other similar development boards; however, the CW32 has advantages.
The project is highly comprehensive and practical, and can be used as a desktop instrument after completion.
The project offers abundant learning materials, including circuit design tutorials, PCB design, code programming learning, and training for engineers' debugging skills.   

II. Hardware Design
1. Power Supply Circuit
Considering that most voltmeter products are used in industrial scenarios with 24V or 36V power supplies, this project selected the 78M05, with a maximum input voltage of up to 35V, as the power supply. It can provide 5V 500mA power.
2. MCU Selection Analysis
This project uses the LCSC CW32F030C8Tx development board (core board) as the main controller, clearly defining the required I/O ports and important peripherals, such as the ADC peripheral. Since this is a development board project, the main purpose is debugging and learning.
3. Voltage and Current Sampling Circuit
4. Voltage Sampling
The voltage divider resistors in this project are designed to be 100K+10K, resulting in a voltage division ratio of 11:1. The divided voltage is then transmitted to the ADS1115 chip, which can detect voltages from 0-5V, with a maximum input voltage of 55V. The ADS1115 provides four channels of 16-bit high-precision voltage sampling . The current
 
sampling circuit
uses the INA240 device, a voltage output, current sense amplifier with enhanced PWM rejection. It can detect the voltage drop across the shunt resistor over a wide common-mode voltage range of –4V to 80V, independent of the supply voltage. Negative common-mode voltage allows the device to operate below ground, thus accommodating the flyback cycle in typical solenoid applications. The enhanced PWM rejection provides a high level of suppression for large common-mode transients (ΔV/Δt) in systems using pulse width modulation (PWM) signals, such as motor drives and solenoid control systems. This feature allows for accurate current measurement without introducing large transients and corresponding recovery ripple in the output voltage. 
The sampling current designed for this project is 6.6A, and the selected sampling resistor (R0) is 10mΩ. The selection of the sampling

resistor mainly needs to consider the following aspects: the maximum value of the pre-designed measurement current (6.6A in this project), the output voltage of 0V-3.3V corresponding to 0A-maximum range current, amplification of 50 times: 3300mV / 50 = 66mV, detection current = 66mV / detection resistor. For example, 5mΩ would be 13.2A.
The power consumption of the current sensing resistor should be considered, and a suitable package should be selected based on this parameter. Considering the power consumption (temperature) issue at high current, a 3W packaged metal wire-wound resistor was selected for this project
. The voltage amplification factor of the current sensing resistor: the A2 series has a magnification factor of 50.

 
5. OLED display:
0.96-inch OLED, 128*64 resolution, SSD1306 driver, I2C communication.
6. Input/Output and Test Points:
1. Test point data is voltage-divided or amplified data, used only for data acquisition, not as input.
2. The top interface connects to the power supply (the chip can only operate with a power supply higher than 5V), and the bottom interface connects to the load, allowing for the acquisition of two separate voltage and current data streams.
 
7. The finished product's
voltage and current acquisition units are mA and mV. Dual-channel
     voltage and current   data
    acquisition.