9. Overview Of NodeMCU/ESP8266


Introduction of ESP8266
NodeMCU is an open source LUA based firmware developed for ESP8266 wifi chip. By exploring functionality with ESP8266 chip, NodeMCU firmware comes with ESP8266 Development board/kit i.e. NodeMCU Development board.
ESP8266 is Wi-Fi enabled system on chip (SoC) module developed by Espressif system. It is mostly used for development of IoT (Internet of Things) embedded applications.

ESP8266 comes with capabilities of
  • 2.4 GHz Wi-Fi (802.11 b/g/n, supporting WPA/WPA2),
  • general-purpose input/output (16 GPIO),
  • Inter-Integrated Circuit (I²C) serial communication protocol,
  • analog-to-digital conversion (10-bit ADC)
  • Serial Peripheral Interface (SPI) serial communication protocol,
  • I²S (Inter-IC Sound) interfaces with DMA(Direct Memory Access) (sharing pins with GPIO),
  • UART (on dedicated pins, plus a transmit-only UART can be enabled on GPIO2), and
  • pulse-width modulation (PWM).
It employs a 32-bit RISC CPU based on the Tensilica Xtensa L106 running at 80 MHz (or overclocked to 160 MHz). It has a 64 KB boot ROM, 64 KB instruction RAM and 96 KB data RAM. External flash memory can be accessed through SPI.
ESP8266 module is low cost standalone wireless transceiver that can be used for end-point IoT developments.
To communicate with the ESP8266 module, microcontroller needs to use set of AT commands. Microcontroller communicates with ESP8266-01 module using UART having specified Baud rate.
There are many third-party manufacturers that produce different modules based on this chip. So, the module comes with different pin availability options like,
  • ESP-01 comes with 8 pins (2 GPIO pins) – PCB trace antenna. (shown in above figure)
  • ESP-02 comes with 8 pins, (3 GPIO pins) – U-FL antenna connector.
  • ESP-03 comes with 14 pins, (7 GPIO pins) – Ceramic antenna.
  • ESP-04 comes with 14 pins, (7 GPIO pins) – No ant.
etc.
For example, below figure shows ESP-01 module pins
ESP8266-01 Module Pin Description

ESP8266-01 Module Pins
  •         3V3: - 3.3 V Power Pin.
  •         GND: - Ground Pin.
  •         RST: - Active Low Reset Pin.
  •         EN: - Active High Enable Pin.
  •         TX: - Serial Transmit Pin of UART.
  •         RX: - Serial Receive Pin of UART.
  •         GPIO0 & GPIO2: - General Purpose I/O Pins. These pins decide what mode (boot or normal) the module starts up in. It also decides whether the TX/RX pins are used for Programming the module or for serial I/O purpose.
 To program the module using UART, Connect GPIO0 to ground and GPIO2 to VCC or leave it open. To use UART for normal Serial I/O leave both the pins open (neither VCC nor Ground).
ESP8266 AT Command Set
Function
AT Commands
Response
Working
AT
OK
Restart
AT+RST
OK
.......
Ready
Firmware Version
AT+GMR
<AT version info> information about AT version
<SDK version info> information about SDK version
<compile time> time of the bin was compiled
OK
List Access Point
AT+CWLAP
+CWLAP:<ecn>,<ssid>,<rssi>,<mac>,<ch>,<freq offset>
OK
Query Joined Access Point
AT+CWJAP?
+CWJAP:<ssid>,<bssid>,<channel>,<rssi>
OK
Join Access Point
AT+CWJAP=”SSID”,”Password”
WIFI CONNECTED
WIFI GOT IP
OK
Quit Access Point
AT+CWQAP
OK
WIFI DISCONNECTED
Get IP Address
AT+CIFSR
(Assuming AT+CWMODE=3)
+CIFSR:APIP,<IP address>
+CIFSR:APMAC,<mac address>
+CIFSR:STAIP,<IP address>
+CIFSR:STAMAC,<mac address>
OK
Query WiFi Mode
AT+CWMODE?
+CWMODE:<mode>
Set WiFi Mode
AT+CWMODE=<mode>
Mode: -
1 = STA (station)
2 = AP (Access Point)
3 = BOTH i.e. STA & AP
OK
Query TCP/UDP Connection
AT+CIPMUX?
+CIPMUX:<mode>
Set TCP/UDP Connection
AT+CIPMUX=<mode>
Mode: -
0 = Single Connection
1 = Multiple Connection
OK
TCP/IP Connection status
AT+CIPSTATUS
STATUS:<status>
Possible statuses are
2: Got IP
3: Connected
4: Disconnected
Query TCP transmission mode
AT+CIPMODE?
+CIPMODE:<mode>
Set TCP transmission mode
AT+CIPMODE=<mode>
Mode: -
0 = Normal mode
1 = Transparent mode
OK
Set up TCP/UDP connection
(CIPMUX=0) AT+CIPSTART = <type>,<addr>,<port>
(CIPMUX=1) AT+CIPSTART= <id>,<type>,<addr>, <port>
Example (CIPMUX=0):
AT+CIPSTART="TCP","192.168.101.110",80
CONNECT
OK
Send Data
(CIPMUX=0) AT+CIPSEND=<data length>
(CIPMUX=1) AT+CIPSEND=<id>,<data length>
OK
> 
(Note: write your data after > and enter it to send it will return status like.)
Recv <data length> bytes
SEND OK
(after we receive response from server if any for default auto receive mode)
(CIPMUX=0): + IPD, <length>: <data>
(CIPMUX=1): + IPD, <id>, <length>: <data>
Close TCP/UDP Connection
AT+CIPCLOSE
CLOSED
OK

NodeMCU Development Kit/Board

NodeMCU Development Kit/Board consist of ESP8266 wifi chip. ESP8266 chip has GPIO pins, serial communication protocol, etc. features on it.
ESP8266 is a low-cost Wi-Fi chip developed by Espressif Systems with TCP/IP protocol.
The features of ESP8266 are extracted on NodeMCU Development board. NodeMCU (LUA based firmware) with Development board/kit that consist of ESP8266 (wifi enabled chip) chip combines NodeMCU Development board which make it stand-alone device in IoT applications.
Let’s see 1st version of NodeMCU Dev Kit and its pinout as shown in below images.


NodeMCU Development Board v0.9 (Version1)
NodeMCU Dev Kit v0.9(V1) Pinouts
2nd version of NodeMCU Dev Kit and its Pinout as shown in below images.
Amica NodeMCU Dev Kit v1.0(Version2)
NodeMCU Dev Kit v1.0(V2) Pinouts

NodeMCU Dev Kit v1.0 pin descriptions

GPIO (General Purpose Input Output) Pins:
NodeMCU has general purpose input output pins on its board as shown in above pinout diagram. We can make it digital high/low and control things like LED or switch on it. Also, we can generate PWM signal on these GPIO pins.
ADC (Analog to Digital Converter) channel (A0):
NodeMCU has one ADC channel/pin on its board.
SPI (Serial Peripheral Interface) Pins:
NodeMCU based ESP8266 has Hardware SPI (HSPI) with four pins available for SPI communication. It also has SPI pins for Quad-SPI communication. With this SPI interface, we can connect any SPI enabled device with NodeMCU and make communication possible with it.
I2C (Inter-Integrated Circuit) Pins:
NodeMCU has I2C functionality support on ESP8266 GPIO pins. Due to internal functionality on ESP-12E we cannot use all its GPIOs for I2C functionality. So, do tests before using any GPIO for I2C applications.
UART (Universal Asynchronous Receiver Transmitter) Pins:
NodeMCU based ESP8266 has two UART interfaces, UART0 and UART1. Since UART0 (RXD0 & TXD0) is used to upload firmware/codes to board, we can’t use them in applications while uploading firmware/codes.

How to start with NodeMCU?

NodeMCU Development board is featured with wifi capability, analog pin, digital pins and serial communication protocols.
To get start with using NodeMCU for IoT applications first we need to know about how to write/download NodeMCU firmware in NodeMCU Development Boards. And before that where this NodeMCU firmware will get as per our requirement.
There is online NodeMCU custom builds available using which we can easily get our custom NodeMCU firmware as per our requirement.

How to write codes for NodeMCU?

After setting up ESP8266 with Node-MCU firmware, let’s see the IDE (Integrated Development Environment) required for development of NodeMCU.
NodeMCU with ESPlorer IDE
Lua scripts are generally used to code the NodeMCU. Lua is an open source, lightweight, embeddable scripting language built on top of C programming language.
NodeMCU with Arduino IDE
Here is another way of developing NodeMCU with a well-known IDE i.e. Arduino IDE. We can also develop applications on NodeMCU using Arduino development environment. This makes easy for Arduino developers than learning new language and IDE for NodeMCU.

Difference in using ESPlorer and Arduino IDE

Well, there is a programming language difference we can say while developing application for NodeMCU using ESPlorer IDE and Arduino IDE.
We need to code in C\C++ programming language if we are using Arduino IDE for developing NodeMCU applications and Lua language if we are using ESPlorer IDE.
Basically, NodeMCU is Lua Interpreter, so it can understand Lua script easily. When we write Lua scripts for NodeMCU and send/upload it to NodeMCU, then they will get executes sequentially. It will not build binary firmware file of code for NodeMCU to write. It will send Lua script as it is to NodeMCU to get execute.
In Arduino IDE when we write and compile code, ESP8266 toolchain in background creates binary firmware file of code we wrote. And when we upload it to NodeMCU then it will flash all NodeMCU firmware with newly generated binary firmware code. In fact, it writes the complete firmware.
That’s the reason why NodeMCU not accept further Lua scripts/code after it is getting flashed by Arduino IDE. After getting flashed by Arduino sketch/code it will be no more Lua interpreter and we got error if we try to upload Lua scripts. To again start with Lua script, we need to flash it with NodeMCU firmware.
Since Arduino IDE compile and upload/writes complete firmware, it takes more time than ESPlorer IDE.

Refrences: https://www.electronicwings.com/nodemcu/nodemcu-development-kitboard

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