ESP8266 WiFi Module Tutorial 2 - WiFi Access Point Mode and TCP Server

In the previous tutorial, we have seen how to make a circuit for the ESP-01 module and we also test the module using AT command. In this tutorial, I will explain how to setup ESP-01 module as an access point and also running a TCP server on it. This is the block diagram that explain the system in this tutorial.

We setup the ESP module by using serial to USB converter and serial terminal software (Hercules). The ESP module is set as an access point and also runs a TCP server on port 23, so any WiFi device such as smartphones or PCs can connects to this access point. We can use TCP client terminal application on the smartphones or PCs for making a connection to the TCP server on ESP module. After the connection is created, we can exchange data with the server.

ESP8266 has 3 modes of operation:

• Mode 1: Station mode. With this mode ESP module act as a WiFi device and can connect to an existing access point.
• Mode 2: Soft AP mode. With this mode ESP module act as a WiFi access point and any WiFi device can connect to it.
• Mode 3: Both station and soft AP mode.

To set the ESP mode, we can use "AT+CWMODE" command. This is the detail explanation of this command from Espressif AT command documentation.

For this tutorial, we want to setup ESP as an access point, so we need to send this command: AT+CWMODE=2. Don't forget to add CRLF ending on every AT command. For the next step, we need to configure the AP by using "AT+CWSAP" command.

For example, we send this command: AT+CWSAP="ESP8266","12345678","4","2". After you configure the AP, you can search and try to connect to this AP from a smartphone. The smartphone will detect this access point:

By default, when we setup ESP module as an AP, the DHCP is on, so the smartphone will get an IP address automatically. We can check the device that connected to this AP by using this command: AT+CWLIF. The response is the list of connected client (IP and MAC address).

We can also ping from the ESP module to smartphone by send this command: AT+PING=192.168.4.2.

From the smartphone, we can also ping to the ESP module (using Android terminal or other ping tools).

Up to this point, ESP module and smartphone is connected in one network, but we still have to setup the TCP connection, so we must create a TCP server on ESP module. To create the TCP server we must send this command: AT+CIPMUX=1 and AT+CIPSERVER=1,80. This is the detail explanation of this command.

After the TCP server is created, on the smartphone we can use a TCP client application to make a connection. If the TCP client is successfully connected, ESP module will return this response: "0,CONNECT" to the serial terminal. If a TCP client is disconnected, ESP module will send this response: "0,CLOSED". "0" is the ID of TCP client.

To send a data from the ESP module to the smartphone, we can use "AT+CIPSEND" command. For example, we send this command: AT+CIPSEND=0,41. "0" means that we want to send data to TCP client channel 0 and "41" means that we want to send 41 characters. After execute that command, you can type the data to be sent on the serial terminal. This is the detail explanation of this command.

Type the message, for example This message is from ESP8266 TCP server. On the smartphone TCP terminal application, this message will be received.

On the TCP client application we can also send a data to ESP module. The data received on ESP module will be in this format:

"0" is the TCP client ID and "41" is the number of received characters.

This tutorial is explain how to manually setup ESP module using serial to USB converter and serial terminal software. Actually, when you use a microcontroller, you don't need a serial to USB converter or serial terminal. But, it will be useful for debugging purpose when you encounter a error when using a microcontroller. This tutorial will also make you familiar with AT command for setup ESP module as a soft AP and TCP server.