CW32 Portable Voltage and Current Meter

Function Description
: Key Functions:
Double-click K1 to enter or exit calibration mode. In calibration mode, click K1 to switch calibration modes.
In calibration mode, click K2 to set the parameter value for the corresponding mode and save it to FLASH. Return to Mode 0.
Five Working Modes:
Mode 0: Displays normal voltage and current values ​​(the upper row of the digital tube displays the voltage value, and the lower row displays the current value)
. Mode 1: 5V voltage calibration setting. The upper row of the digital tube displays 5.05. The lower row displays the current voltage value. In this mode, the multimeter should be set to 5.00V to measure the measured value. Pressing K2 will calibrate the current value to 5V.
Mode 2: 15V voltage calibration setting. The upper row of the digital tube displays 5.15. The lower row displays the current voltage value. In this mode, the multimeter should be set to 15.0V to measure the measured value. Pressing K2 will calibrate the current value to 15V.
Mode 3: 0.5A current calibration setting. The top row of digital tubes displays A.0.5. The bottom row displays the current current value. Pressing the K2 key sets the current value to 0.5A.
Mode 4: Current 1.5A calibration setting. The top row of digital tubes displays A.1.5. The bottom row displays the current current value. Pressing the K2 key sets the current value to 1.5A.
Charging: Insert TYPE-C for charging. Charging time is approximately 1 hour, and the charging current is 580mA. The charging indicator light is red when charging and green when fully charged.
Schematic
1. Power Management:
The device uses a 600mAh battery as the main power source. Through an AMS1117 voltage regulator, the battery voltage is converted to a stable 3.3V voltage to meet the power supply requirements of the development board. The device charges via a TYPE-C interface using a TP4056 charging module. The charging current is set to 580mA to ensure a balance between charging speed and battery health. To save power, the device has a sliding switch that can disconnect the battery power supply when the device is not in use, thereby extending battery life.
2. Voltage Sampling Circuit:
The voltage divider resistors in this project are 220K+10K, resulting in a voltage division ratio of 22:1. The ADC reference is 1.5V, which can be configured via the program. The maximum voltage to be measured is 0-30V for safety reasons.
3. Current Sampling Circuit:
This project uses a low-side current sampling circuit for current detection. The low-side of the sampling circuit is grounded to the development board via a 0Ω resistor. The current input range is 0-3A, the sampling resistor is 2512 100mΩ, the accuracy is ±1%, and the power is 1W.
4. Digital Display:
This project uses two 0.28-inch three-digit common-cathode digital tubes as display units.
5. TL431 Circuit Design for Voltage Measurement Calibration:
This project adds an additional TL431 circuit to provide a 2.5V reference voltage, which can be used to provide an external voltage reference for ADC calibration.
The PCB layout and physical diagram show
a board size of 56x74mm and a 3D shell size of 60x82x18mm.
The button uses a horizontal, side-mounted interface for
testing voltage and current, which is a screw-type terminal block. This type of terminal block provides a reliable electrical connection, ensuring stable current transmission. Screw-type terminals are relatively simple to operate, generally requiring only a screwdriver to complete the wiring, improving testing efficiency.
The battery connection uses a pluggable terminal block for easy connection and disconnection during debugging.
Important
Notes:
1. Power Supply: Since the battery's maximum voltage is 4.2V, after being converted to 3.3V by the AMS1117, the output is not 3.3V, but approximately 2.8V in actual measurements. Since the CW32 microcontroller operates between 1.65V and 5.5V, normal use is fine. However, the brightness of the digital tube may decrease over time. The AMS1117 is used to utilize existing stock; if this is a concern, you will need to modify the LDO yourself.
2. 3D Housing Issues: Due to the small height design, the upper housing cannot be installed. Since we didn't want the development board soldered to the base plate, we had to forgo the housing and use the bare board directly.
3. Program Issue: Due to changes in the PCB layout, the I/O ports have been modified, resulting in a mismatch with the training camp's PCB. Please refer to the schematic for details. There are two buttons, so their functions differ.
A demonstration of the calibration function
is in the attached video .