[LCSC Development Board] CW32 Voltage and Current Meter

Design Background:

ADCs (Analog-to-Digital Converters) are indispensable key components in electronic systems. They convert continuous analog signals into digital signals, enabling digital processing and analysis.
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.
In this project, I learned how to design from scratch and use LCSC EDA to implement the above ideas.

Core Hardware Circuit Analysis: LDO
Power Supply Circuit
: The above power supply circuit can receive 5-12V DC power. A diode is added to prevent reverse connection of the power supply. Afterwards, the input DC power undergoes multiple filtering (high frequency and low frequency) through capacitors. Then, an LDO linear regulator converts the input 5-12V power supply into a stable 5V output, providing the power foundation for the other circuits.
The VP mentioned above does not pass through a linear regulator, so the voltage at this point is actually equal to the input voltage. Connecting this VP to the top regulator, and using different jumper connections, we can directly read the voltage at this point using only the ADC. This facilitates testing of
the top-adjustment voltage
measurement circuit. The voltage measurement circuit
uses a voltage divider resistor to perform a voltage division (22:1), allowing its ADC to acquire the voltage from 0 to vref. The original voltage can then be obtained through calculation.
Current Measurement Circuit
Design Analysis:
The sampling current designed for this project is 3A, and the selected sampling resistor (R0) is 100mΩ.
The selection of the sampling resistor mainly needs to consider the following aspects:
the maximum value of the pre-designed measurement current, which in this project is a 3A
current sensing resistor. It is generally not recommended to exceed 0.5V.
The power consumption of the current sensing resistor should be selected according to this parameter. Considering the power consumption (temperature) problem under high current, a 1W packaged metal wire-wound resistor was selected in this project
. The voltage amplification factor of the current sensing resistor: No operational amplifier was used to build the amplification circuit in this project, so the factor is 1.
Then, the current sensing resistor value can be calculated using the above parameters. Selection:
Since This project does not use an amplifier circuit, therefore a larger sampling resistor is needed to obtain a higher measured voltage for measurement.
Considering that a larger resistor will result in a larger voltage drop and higher power consumption, an unlimited selection of a larger resistor is not possible.
This project uses a 1W package resistor, corresponding to a power consumption of 1W.
Based on the above data, a 100mΩ current sensing resistor was selected. According to the formula, 3A * 100mΩ = 300mV, 900mW can be calculated.
To cope with different usage environments, especially high current scenarios, the R0 resistor can be replaced with constantan wire or a shunt. The replacement can be chosen according to the actual usage scenario. For safety and educational purposes, this project will not discuss measurements exceeding 3A, but the principle is the same. The current project uses
a digital tube display circuit
. After reading the ADC data, it is displayed on the digital tube, allowing the user to intuitively see the test results. I accidentally broke a CW32 pad, causing the A segment of the digital tube to malfunction. However, this does not actually affect usage. If a new CW32 is replaced, it will work normally.
One more thing to note is that the pin headers on my CW32 currently need to be soldered upwards. This is because I mistakenly reversed the pin header sockets during circuit board design. Because I accidentally removed the pads controlling segment A of the digital display while removing the pin headers, segment A did not display in the actual demonstration, but the project itself is correct.
Please refer to the project file developed by LCSC; most of my code is copied from it.
https://oshwhub.com/li-chuang-kai-fa-ban/cw32-shu-zi-dian-ya-dian-liu-biao-kai-fa-ban-tao-jian