A Pikachu voltage and current meter based on the LCSC GeoStar-CW32 development board

Project Overview:
This project utilizes the LCSC CW32F030C8T6 development board to create a voltmeter and current meter. It can detect voltages from 0-30V and currents from 0-3A. Using the CW32 MCU enables high-precision measurements because the CW32 chip has an internal 12-bit high-speed ADC and a built-in reference voltage, allowing for better and more convenient voltage and current detection.
 
Application Scenarios:
In everyday electronic circuit use, it's often necessary to measure voltage and current. This voltmeter and current meter is compact and small, only the size of a palm, making it easy to carry. It can be powered by the power supply being tested, eliminating concerns about power outages. It's a great helper for home and travel.
 
Project Parameters:

The voltage measurement section uses two voltage sampling ranges: one for a wide range of 0-30V and the other for high-precision 0-3V.
The power supply section provides a measurement range of 0-3A.
It also features onboard analog voltage and current measurements to meet its own voltage and current calibration requirements.
Three onboard buttons allow for modification of the display mode and calibration of voltage and current settings.

 
Hardware Schematic Display:
Overall Schematic Preview;
 
Development Board Pin Connection Circuit Display:
 
Power Supply Schematic Display:
The power supply section uses an LDO (Low Dropout Linear Regulator). To accommodate a wider range of voltages, the SE8550K2 with a maximum input voltage of 40V was chosen. Because the LDO's transformation is linear, it causes less interference to other components, eliminating the possibility of power supply interference affecting our voltage and current measurements. A 1N5819 diode is connected in series at the power supply front end to protect against reverse connection issues, effectively protecting the downstream circuitry. A 10-ohm resistor is also connected in series as a fuse to prevent short circuits and damage to the board. The power supply section also uses parallel capacitors of varying sizes for filtering. The current first passes through the large capacitor for low-frequency interference filtering, and then through the small capacitor for high-frequency interference filtering, ensuring a stable and clean power supply to the LDO device. The LDO output section performs the same operation. An LED is also used to indicate the power supply status; it lights up when the power supply is functioning correctly.
 
Voltage acquisition schematic diagram:
 
External reference voltage schematic diagram:
This project uses the CW32's internal reference voltage. This circuit is included to facilitate designing and using chips without internal reference voltages later. An external reference voltage is provided by a TL431 to offer a 2.5V reference voltage.
 
The schematic diagram of the analog voltage section is shown below:
 
The wiring diagram of the voltage measurement section is shown below.
In the diagram, +V and GND are the positive and negative terminals of the voltage to be measured, respectively. At the same time, the positive terminal of the voltage to be measured can be connected to VP to power the whole system, which is more convenient and eliminates the need to prepare a separate power supply for the system. However, it should be noted that when the voltage of the power supply under test is lower than 5V, it will not be able to provide power to the system, and a separate power supply is required. In addition, for the convenience of later debugging, a 2mm banana plug for multimeter probes is used here. The multimeter probes can be directly inserted into the banana plug, which is more convenient and frees up your hands.
 
The schematic diagram for the current measurement section is shown below.
The essence of current measurement is still voltage measurement. By measuring the voltage across the measured current, the purpose of current measurement is achieved. Here, R11 is used as the sampling resistor. Because the current measurement range is limited to 0-3A, a 100mΩ resistor is chosen for sampling. Also, due to the large current, the resistor's power rating should be at least 1W. A 1kΩ resistor is placed before the measurement I/O port to limit the current and prevent damage to the I/O pins from excessive current. Together with C9, it acts as a filter for noise reduction. A 1N4148 is also placed here, serving a similar purpose to protect the ADC pins.
 
The schematic diagram for the analog current section is also shown below.
When using the onboard analog current section, remember not to solder the sampling resistor R11 beforehand, otherwise it will affect the normal measurement of the analog current. The analog current measurement is calculated by dividing the voltage across the resistor by its resistance value and then multiplying by 100, which can simulate a current of 0-2.38A for ADC measurement. (Note whether this part of the software code is set up this way.)
 
Current measurement port connection schematic diagram:
 
Example diagram of digital tube display:
Voltage and current measurements are displayed using two 0.28-inch common cathode three-digit digital tubes. Two different colored digits can be selected for more detailed differentiation of the measured values.
 
Button schematic diagram:
Three buttons are used to "calibrate," "confirm," and "return" the device. The specific control logic of the buttons will be explained in the finished product demonstration section.
 
IO test schematic diagram:
Test LEDs are used to check if the code framework is working correctly and if the test LED on the device can be lit normally.
 
Other schematic diagrams:
A serial port for debugging is brought out from the board for easy addition of other modules later.
 
PCB Display:
 
PCB Body Preview (Front):
The PCB utilizes JLCPCB's color silkscreen printing technology, with text markings on each terminal for a clearer understanding of their function. The silkscreen text also features a distinctive design, complementing the "Pikachu" motif. Since this device is a voltage and current meter, Pikachu, the electric mouse from Pokémon, was chosen as the mascot to ensure stable and reliable voltage and current measurements. PCB Body Preview
(Back): PCB 3D Preview
(Front): PCB 3D Preview
(Back):
PCB Housing Display:
The housing consists of two main parts, top and bottom. The top cover is connected to the housing via a thermocouple nut, which will be indicated in the product description.
 
Housing Panel Display:
 
Actual Product Display:
The PCB is very attractive, with clear and vibrant color silkscreen printing. The integrated gold plating further enhances its appearance.
Soldered PCB Display:
During soldering, some design issues were discovered. The initial design intended for the development board to plug into the expansion board, but this resulted in a large, less compact casing. Therefore, the development board was directly soldered to the expansion board via headers, significantly reducing the casing height. However, this also presents some drawbacks: the development board cannot be removed, making troubleshooting difficult. Also, while the height is reduced, the Type-C port on the development board is blocked by the electrolytic capacitors, preventing connection to the Type-C port. Another modification was the jumper headers on the development board. Originally straight-pronged, they were replaced with angled headers to maintain a cleaner, more aesthetically pleasing casing. This allows for jumper functionality without affecting the casing height. Later, we found several areas for optimization. For example, the wire-to-board terminals could be replaced with horizontal sockets, allowing the housing opening to be placed on the side, improving the aesthetics of the front panel. Also, potentiometers with shorter handles could be chosen, as the onboard analog voltage and current sensors are rarely used after calibration, so shorter potentiometers can be used and hidden within the housing.
 
Software:
The software directly uses the official example without much modification. However, it's important to note some issues during CW32 code setup and usage. The official documentation provides detailed instructions: CW32 Digital Voltage and Current Meter Training Camp Project Tutorial Document | LCSC Development Board Technical Documentation Center (lckfb.com). Following the official steps should generally resolve most issues.
Note that if you encounter errors after compiling and downloading the code, remember to check if the chip selection is correct.
 
The code includes detailed comments on the button functions, facilitating modifications to the button operation logic within the code.
 
 
Outer Shell:
The outer shell is connected by four M3 screws, and the top cover is connected to the bottom of the outer shell by four embedded M3 thermosetting nuts. The M3 screws are 8mm long, and the thermosetting nuts are 3*6*4.2mm in size.
 
Finished Product Display:
 
 
The button caps used here are model A101 black silicone button caps with 6*6 tactile switches, 7.5H or larger, inner diameter 3.0 feet, 7.4*4.5 (20 pieces - Taobao.com).
The banana socket used here is available for purchase: 2mm banana socket, pure copper gold-plated K2A33, 2mm test hole circuit experimental teaching instrument circuit board - Taobao.com.
 
Project Summary:
This project still has many areas for improvement. Through this project of making a voltmeter and ammeter, I learned a lot about voltage and current measurement and ADC, which will be of great help in future circuit design.