How to see the voltage of the output on LCD?
The type of device created for this sort of situation is called panel meter.  A modern panel meter is an LCD display (or an LED display) with a built-in ADC (analog to digital converter).  

A typical panel meter is hard-wired (as opposed to programmable).  It takes a certain range of voltages and displays it.


Here's a sample of a run-off-the-mill LCD panel meter.
Notice that it has got few outside connections: voltage to measure, power, ground.