USB power meter

This project is based on the CW32F030C8T6 development board. A 0.96-inch 13-pin TFT display shows real-time voltage, current, power, temperature, and humidity. A CH224 protocol chip is added to support 5-20V voltage output.
1. Project Introduction:

This project is a training project for the CW32 digital voltmeter and ammeter training camp. After fully understanding the training project, the following modifications were made:

The LDO circuit was removed, and the onboard USB power supply was used directly.
The digital tube was replaced with a TFT display for better display effects.
All surface-mount resistors and capacitors were replaced with 0603 packages to reduce size.

2. Hardware Design:

The project requires the use of a development board, so only the external application circuit needs to be designed separately and then connected to the development board via pin headers in the form of an expansion board.

[Hardware Design.png]
2.1 Power Supply Design:

Due to the lack of a DC power supply and considering the compact size of the expansion board, the external LDO circuit was removed, and the USB input of the development board was used directly as the power supply.

Power Supply Design.png
2.2 Voltage Sampling:

The voltage is input to the ADC of the core board using a dual-range sampling method. When using the ADC's internal 1.5V reference voltage, R5 (10kΩ) and R8 (10kΩ) can measure the voltage between 0-3V through a voltage divider, while the voltage divider circuit composed of R3 (220kΩ) and R7 (10kΩ) can measure the voltage between 0-34.5V.

Voltage Sampling.png
2.3 Current Sampling:

Current sampling uses a 100mΩ sampling resistor. Based on the 3A design range, its power must be at least 900mW.

Current Sampling.png
2.4 Analog Input:

For convenient functional testing, the voltage and current are directly controlled from the power supply through two potentiometers, connected to the sampling circuit using jumper caps.

Analog Input.png
2.5 Display Output:

The output section has been modified to output the measured values ​​using a TFT display screen, which is far superior to a digital tube in both price and display effect.

Display Output.png