A Digital to Analog Converter (DAC takes a digital value and produces a corresonding voltage or current, depending on type, output. How, exactly, and withholding no details, do you intend to measure "pull-in and drop-out voltages of a relay", or, for that matter, anything else, when all you can do is to put out an analog voltage?

What, exactly, are you planning to learn. Relays are typically current-driven devices and, most often, don't care a whit about what the source voltage is, though there are, of course, restrictions. How are you determining that the relay has closed? How are you determining that the relay has opened? How do you process contact bounce? What about contact resistance?

BTW ... an 8-bit converter, whether DAC or ADC, has no more than 256 values that it can support/provide. For each such value, you can have a table entry consisting of the desired text string that should appear on your LCD module. If, for example, there are 4 such characters in each string, then you can take the 8-bit value, multiply it by four, and use that value as an offset (index) into the table. You could even build a second table that contains the addresses of the 4-byte strings, then load the two-byte address into DPTR then MOVC the four values to internal memory, and from there to the LCD. The LCD is very, Very slow, so you have plenty of time.

RE