Safe to connect SIM800L v2 to GPIOs direct?

[leenowell]

Hi,

I have bought one of these blue SIM800L v2 boards ( https://www.aliexpress.com/item/1005007 ... 18029BPwAs ) to connect to my ESP32. It takes a power supply of 5v (will have a separate one to my ESP32) but I am confused as to whether the tx and rx pins can be connected to the GPIOs directly and also what VDD does. Some specs online imply that the voltage of the tx and rx pins are 5v, others imply they are the same as SIM800L chip supply (3.4v to 4.4v) and others 3.3v. From what I can find online, the VDD pin may be a reference voltage for the tx/ rx pins so was thinking maybe I should connect that up to the 3.3v output from the ESP32 board?

I have connected the 2 power pins to a 5v supply and my DMM across the other gnd and tx pins and it seems to vary between 3v and 2.5v. So... it implies it should be ok to connect them up directly to the GPIOs but wanted to see if anyone knows what the actual spec of the board is /had experience with these boards?

Many thanks in advance for your help

Lee.