I have been studying the ESP8266 module, and am successfully sending it AT commands on a development board. As it stands now, I am operating through a development board which has a mini-USB input from my Nano. I assume though, that if I went in with a direct serial connection from the Nano, to the serial input to the ESP8266, I would also be able to issue AT commands, and get responses. Is this true?
Second question. I've seen wiring diagrams directly hooking the Nano (or Uno) serial to the ESP8266, although the latter is a 3.3v device. So, is the ESP8266 5 volt tolerant, or are only maybe some of them 5v. tolerant?
All of them MAY tolerate 5V. But they are officially 3V3 devices. Just because some schmo wrote instructions online, doesn't mean he has a clue. Lots of "it's working for me, for now" should not be reassuring. Voltage regulation is simple. LM1117 for the power, 2 resistors for the logic level shifting.
I have no idea what this means "I am operating through a development board which has a mini-USB input from my Nano. "
Firstly, what kind of ESP8266 board do you have? There are many. ESP-01 through ESP-12, NodeMCUs, Wemos, etc.
Secondly, how do you have it hooked up to your Nano?
The board I bought is a Chinese EBay product, and the only title on it is ESP8266 SDK. It is in fact, for $10.00, a lot of board, and very well made. Contains RGB LED, relay, buzzer, DHT11, and other odds and ends which can be toggled into the ESP8266 on various pins via a DIP switch. Even arrived in only two weeks.
I probably will do the little extra bit of work for level shifting, since I am only going to attach it by serial to a Nano, and I've got a great stock of 2N7000's. (And just what is wrong with a Nano? I use 'em for nearly everything, unless I need more horsepower or memory.)
The main question I asked was, can I access the AT command interface of the ESP8266 by just connecting via a serial interface to a Nano. You didn't address that, but it's easy enough to try.
What I meant about asking why you're using a Nano, and now that you're saying for the 'horsepower', is because the ESP8266 outspecs the Nano, in case you weren't aware. Nano 16MHz, ESP8266 80MHz, at least double the memory, etc.
Meaning, what purpose is the Nano serving if your project, whatever it is, could be done just on the ESP8266 itself? Yes an Arduino can communicate serially to an ESP8266. But it begs the question. Consider if you even need to.
You can program the esp8266 directly in the Arduino IDE without using the nano at all. There is a nice interface you can load in the board manager. Then just upload sketches. You just need a serial interface to your computer. (Unless its like a wemos d1 mini which has the serial built in)
And yes, its safest to level translate the serial lines to 3.3 v.