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Crowtail- Serial Wifi


The serial wifi module based on ESP-12.which is an ultra-low power UART-WiFi module. It has excellent dimensions and ULP technology compared to other similar modules. The module is special design for mobile devices and Internet of Things . Once firmware is upgraded to the appropriate version, a compatible Android device can run the IOT.APK to do the following:control the PWM, I/O pin, or Serial communication. For example,you can use this module transmit date with it serial port.It is easy to communication with other device.

Model: CT0019SW

Crowtail-Serial Wifi.JPG


  • Connection Mode:U(UART)
  • One high speed serial port
  • Working voltage:5v
  • 802.11 b/g/n protocol
  • Wi-Fi Direct (P2P), soft-AP
  • Integrated TCP/IP protocol stack
  • Integrated TR switch, balun, LNA, power amplifier and matching network
  • Integrated PLL, regulators, and power management units
  • +19.5dBm output power in 802.11b mode
  • Dimensions(mm):45.0(L)x20.0(W)x6.8(H)

Electronic Characteristics

1.Current Consumption

The following current consumption is based on 3.3V supply, and 25℃ ambient, using internal regulators. Measurements are done at antenna port without SAW filter. All the transmitter’s measurements are based on 90% duty cycle, continuous transmit mode.

Mode Min Typ Max Unit
Transmit 802.11b, CCK 1Mbps, POUT=+19.5dBm 215 mA
Transmit 802.11b, CCK 11Mbps, POUT=+18.5dBm 197 mA
Transmit 802.11g, OFDM 54Mbps, POUT =+16dBm 145 mA
Transmit 802.11n, MCS7, POUT=+14dBm 135 mA
Receive 802.11b, packet length=1024 byte, -80dBm 100 mA
Receive 802.11g, packet length=1024 byte, -70dBm 100 mA
Receive 802.11n, packet length=1024 byte, -65dBm 102 mA
Total shutdown 0.5 uA

2.RF Performance

The following are measured under room temperature conditions with 3.3V and 1.1V power supplies.

Description Min Typical Max Unit
Input frequency 2412 2484 MHz
Input impedance 50 Ω
Input reflection -10 dB
Output power of PA for 72.2Mbps 14 15 16 dBm
Output power of PA for 11b mode 17.5 18.5 19.5 dBm
CCK, 1Mbps -98 dBm
CCK, 11Mbps -91 dBm
6Mbps (½ BPSK) -93 dBm
54Mbps (¾ 64-QAM) -75 dBm
HT20, MCS7 (65Mbps, 72.2Mbps) -71 dBm




ESP8266 Schematic.jpg

Application Notes

  • Smart power plugs
  • Home automation
  • Mesh network
  • Industrial wireless control
  • Baby monitors
  • IP Cameras
  • Sensor networks
  • Wearable electronics
  • Wi-Fi location-aware devices
  • Security ID tags
  • Wi-Fi position system beacons

AT Commands


  • Baud rate at 115200
  • x is the commands

ESP8266 AT Test.png

(Click the picture to zoom in)

Set Inquiry Test Execute
AT+<x>=<…> AT+<x>? AT+<x>=? AT+<x>
Set the network mode Check current mode Return which modes supported -


  • carefully there are must be no any spaces between the " and IP address or port
Commands Description Type Set/Execute Inquiry test Parameters and Examples
AT general test basic - - - -
AT+RST restart the module basic - - - -
AT+GMR check firmware version basic - - - -
AT+CWMODE wifi mode wifi AT+CWMODE=<mode> AT+CWMODE? AT+CWMODE=? 1= Sta, 2= AP, 3=both, Sta is the default mode of router, AP is a normal mode for devices
AT+CWJAP join the AP wifi AT+ CWJAP =<ssid>,< pwd > AT+ CWJAP? - ssid = ssid, pwd = wifi password
AT+CWLAP list the AP wifi AT+CWLAP
AT+CWQAP quit the AP wifi AT+CWQAP - AT+CWQAP=?
AT+ CWSAP set the parameters of AP wifi AT+ CWSAP= <ssid>,<pwd>,<chl>, <ecn> AT+ CWSAP? ssid, pwd, chl = channel, ecn = encryption; eg. Connect to your router: AT+CWJAP="","helloworld"; and check if connected: AT+CWJAP?
AT+CWLIF check join devices' IP wifi AT+CWLIF - -
AT+ CIPSTATUS get the connection status TCP/IP AT+ CIPSTATUS <id>,<type>,<addr>,<port>,<tetype>= client or server mode
AT+CIPSTART set up TCP or UDP connection TCP/IP 1)single connection (+CIPMUX=0) AT+CIPSTART= <type>,<addr>,<port>; 2) multiple connection (+CIPMUX=1) AT+CIPSTART= <id><type>,<addr>, <port> - AT+CIPSTART=? id = 0-4, type = TCP/UDP, addr = IP address, port= port; eg. Connect to another TCP server, set multiple connection first: AT+CIPMUX=1; connect: AT+CIPSTART=4,"TCP","X1.X2.X3.X4",9999
AT+CIPMODE set data transmission mode TCP/IP AT+CIPMODE=<mode> AT+CIPSEND? 0 not data mode, 1 data mode; return "Link is builded"
AT+CIPSEND send data TCP/IP 1)single connection(+CIPMUX=0) AT+CIPSEND=<length>; 2) multiple connection (+CIPMUX=1) AT+CIPSEND= <id>,<length> AT+CIPSEND=? eg. send data: AT+CIPSEND=4,15 and then enter the data.
AT+ CIPMUX set mutiple connection TCP/IP AT+ CIPMUX=<mode> AT+ CIPMUX? 0 for single connection 1 for multiple connection
AT+ CIPSERVER set as server TCP/IP AT+ CIPSERVER= <mode>[,<port> ] mode 0 to close server mode, mode 1 to open; port = port; eg. turn on as a TCP server: AT+CIPSERVER=1,8888, check the self server IP address: AT+CIFSR=?
AT+ CIPSTO Set the server timeout AT+CIPSTO=<time> AT+CIPSTO? <time>0~28800 in second
+IPD received data For Single Connection mode(CIPMUX=0): + IPD, <len>: For Multi Connection mode(CIPMUX=1): + IPD, <id>, <len>: <data>


Use the ESP8266-12 and Arduino as a Webserver

1.Hardware Connection. Connected the Serial Wifi to U2 of the Crowtail- base shiled( D2 and D3) are used as software UART. Baud Rate:9600. Esp8266hardware11.jpg

2.Connect the board to PC using USB cable.

3:Download the code: WWebserver for ESPduino or copy it to you new skecth.

#include <SoftwareSerial.h>

#define DEBUG true

SoftwareSerial esp8266(2,3); // make RX Arduino line is pin 2, make TX Arduino line is pin 3.
                             // This means that you need to connect the TX line from the esp to the Arduino's pin 2
                             // and the RX line from the esp to the Arduino's pin 3
void setup()
  esp8266.begin(9600); // your esp's baud rate might be different
  sendData("AT+RST\r\n",2000,DEBUG); // reset module
  sendData("AT+CWMODE=2\r\n",1000,DEBUG); // configure as access point
  sendData("AT+CIFSR\r\n",1000,DEBUG); // get ip address
  sendData("AT+CIPMUX=1\r\n",1000,DEBUG); // configure for multiple connections
  sendData("AT+CIPSERVER=1,80\r\n",1000,DEBUG); // turn on server on port 80

void loop()
  if(esp8266.available()) // check if the esp is sending a message 
      // The esp has data so display its output to the serial window 
      char c =; // read the next character.
    } */


     int connectionId =; // subtract 48 because the read() function returns 
                                           // the ASCII decimal value and 0 (the first decimal number) starts at 48

     String webpage = "<h1>Hello World!</h1>";
     String cipSend = "AT+CIPSEND=";
     cipSend += connectionId;
     cipSend += ",";
     cipSend +=webpage.length();
     cipSend +="\r\n";


     String closeCommand = "AT+CIPCLOSE="; 
     closeCommand+=5; // append connection id

String sendData(String command, const int timeout, boolean debug)
    String response = "";

    esp8266.print(command); // send the read character to the esp8266

    long int time = millis();

    while( (time+timeout) > millis())
        // The esp has data so display its output to the serial window 
        char c =; // read the next character.

    return response;

4.Upload the code and Open the serial monitor.You can see some configuration information.


5.PC connect to the wifi of ESP8266.


6.Then you can visit the Webserver of the ESP8266.


Upgrading ESP8266 Firmware

How to upgrade ESP8266 firmware?

We use NodeMCU flasher here, the download links:

Note: use nodemcu flasher to flash Firmware to ESP8266, its default firmware is Lau language. If you want to flash AT Commands firmware, go to ESP8266 forum to get one.

1. Connect your ESP8266 module as follows:

  • Vcc = 3.3V (needs around 300-400mA peak)
  • Gnd = -ve ground
  • CH_PD = Chip enable so always +ve
  • RST = Leave floating or ground to reset
  • GPIO0 = Normally floating but this needs to be grounded when you start the update.
  • GPIO2 = high level
  • UTXD = Tx data connect to RX on FTDI/Serial interface
  • URXD = Rx data connect to TX of FTDI/Serial interface

English Version: Please refer to the NodeMCU flasher user guide.

Chinese Version: Please see the next step below

2. Open the software, choose the right COM and click the button that is circled in the following picture. When a tick appears in the bottom-left corner, it suggests that the firmware upgrade successfully.

Upgrade Firmware.jpg

3. This software contains an existing firmware, but if you want to upgrade other ESP8266 firmware, please click the button that is circled in the following picture, and only two file paths are available to choose.

Upgrade Firmware 1.jpg

Other ways of ESP8266 firmware upgrading