eBay LM2596 Power Converter Module DC 4.0~40 to 1.3-37V LED Voltmeter
Channel: Elecifun
Date: 2016-03-15

This little Buck Converter has a voltage display and the procedure for calibrating input and output voltages. I cant seem to calibrate the input voltage but the output seems fine.
eBay LM2596 Power Converter Module DC 4.0~40 to 1.3-37V LED Voltmeter