LM2577S is a boost voltage module with digital voltmeter display. The error range of voltmeter is ±0.1V , and the measuring range is 0~40V. Touch slightly the key to measure input or output voltage. There is a indicator light showing which circuit is being measured. It has non-volatile memory, namely, it can indicate the voltage value measured last time after connecting circuit. Keep pressing the key slightly for 3 sec , and the LED display off; touch slightly the key again , and the LED on. It is convenient to use this module with terminal under no soldering iron and the module can keep soldering wire connection. Maximal output current is up to 2.5A.