An S0 connector itself does not output a voltage; the levels in that document specify what voltage you can apply to it externally without it breaking. Technically applying 3.3V is outside the specs (it says minimum is 3.3V) but I imagine it works with most meters anyway. Thank you a lot . Now I'm b...

I just try a project to counting pulse signal from electric meter. I was found a schematic from this guy . He pull-up digital pin to 3.3V VCC then connect to S0+, gnd from esp to S0- https://community.home-assistant.io/t/pulse-counter-configuration-esp8266-and-energy-meter-with-s0-interface/650061 h...