The 6.5-40V to 5V 2A USB Charger is a versatile and convenient module that serves two primary functions. Firstly, it acts as a step-down voltage converter, allowing you to take input voltages ranging from 6.5V to 40V DC and convert them to a fixed 5V DC output. This feature makes it suitable for a wide range of applications, including charging smart devices, powering development boards, and other electronics projects that require a stable 5V power supply. Secondly, the module includes an onboard voltmeter with a 3x7-segment display. This voltmeter functionality allows you to measure input voltages between 4.5V and 40V with good precision. This makes it a handy tool for electronics makers who need to measure voltages on-the-go, without the need for additional equipment. Calibrating the voltmeter is a straightforward process and can be done in three simple steps: Step 1: Activate calibration mode by pressing and holding the "Output Enable" button for 2 seconds. The voltmeter display will start flashing, indicating that it is in calibration mode. Step 2: Adjust the voltage reading by pressing the "Output Enable" button to increase the voltage reading by 0.1V per unit or the "Low Power" button to decrease it by 0.1V per unit. Match the voltmeter reading to the voltage supplied to achieve high-precision calibration. Step 3: Exit the voltage calibration mode by pressing and holding the "Output Enable" button for 2 seconds again. The board will automatically save the calibration parameters even if the power is disconnected. It is recommended to use a lab power supply or a reliable power source with known voltages and currents to calibrate the module accurately. This ensures that the voltmeter provides precise readings for your specific projects. Overall, the 6.5-40V to 5V 2A USB Charger with voltmeter is a valuable tool for electronics enthusiasts and professionals, offering both a stable 5V power supply and convenient on-the-go voltage measurement capabilities.