Conrad 10215 Operation Manual

BEFORE WE START

When you first connect the IoT-WiFi-board (hereinafter also:
NanoESP-) the computer may not find the required driver for the USB-to-Serial con­verter automatically. In this case, download the driver from

www.iot.fkainka.de/driver and install it manually. The Arduino- software will then

permit you to set the port and the board Arduino Nano (CPU: Atmega328). The
controller should then be ready to use.

You also need to make some settings for working with the serial monitor. The
Baud rate used is 19200 Baud. To send commands, you also need to select the

options CR and NL next to the menu for the Baud rate.

The proper settings in the Arduino environment

I worked with Arduino IDE versions 1.6.5 – 1.6.6. Older versions may cause prob­lems. The current Arduino IDE version is available on the website

www.arduino.cc.

If you have any difficulties or problems with the board or the learning package, you

can visit www.iot.fkainka.de for help. The page also contains a forum, new user
projects and all programs presented here in the latest version.

The learning package contains a pinboard on which you can pin the
NanoESP as illustrated below. This leaves you the most space for experiments,
while the WLAN module protrudes over the plug board at the rear. The Micro USB
cable can then be plugged in as shown in the picture in the following section and
will barely be in the way. More detailed setup images are enclosed with the indi­vidual chapters.

The IoT-WiFi-board (NanoESP)

The main element of this learning package is the IoT-WiFi-board (NanoESP). As
you can see quite well on the PCB, the board is made up of two components. The
left half is an Arduin-compatible micro controller system that can be compared to
the Arduino Nano. The right part is the WLAN module with the designation

ESP8266.

These two components communicate via a serial interface generated by software.

The NanoESP on the plug board

The pin layout of the board

The board has many different elements, such as the pins, some of which have
special functions, or the LEDs, the function of which is not always evident at first
glance. To prevent you from losing the overview, the following image lists the most
important functions of the individual elements.

The most important pins and designations of the board

The WLAN module is controlled with AT commands. For this, the Arduino part of
the board is connected to the WLAN module via pins 11 and 12. A small circuit
converts the 5-V-levels into compatible 3.3-V-levels. Pins 11 and 12 should not be
used in your own projects for this reason.

Further important hardware properties of the board are summarised in the follow­ing table.

Technical Data

Microcontroller: ATmega328
Flash memory: 32 kB (including 0.5 kB for the boot loader)
SRAM: 2 kB
EEPROM: 1 kB
Cycle rate: 16 MHz
I/O-pins: 20 (including 2 for communication with the WLAN

module)

U

including PWM: 6

U

including analogue inputs: 6

USB-to-Serial chip: CH340G
Operating voltage: 5 V
Recommended input voltage: 7 – 12 V
Maximum current per I/O-pin: 40 mA
Resilience of the 3.3-V-output: 50 mA

WLAN-module: ESP8266
SPI-Flash 4 Mbit
Operating voltage: 3.3 V
WLAN standards: 802.11 b/g/n
WLAN modes: Wi-Fi Direct (P2P), Soft-AP
Firmware: AT-Firmware Version 0.22
Other Features: Integrated TCP/IP-stack
+19.5 dBm output power in the 802.11b-mode
Integrated Low-Power-32-bit-CPU
Communication via UART

COMPONENTS IN THE
LEARNING PACKAGE

Find an overview of the parts contained in the learning package below.
1 IoT-WiFi-board (NanoESP)
1 pinboard
1 m circuit wire
2 button
1 9-V-clip
1 LED (red)
1 RGB-LED (4 connection legs)
1 resistor 10 kOhm (brown-black-orange)
1 resistor 1 kOhm (brown-black-red)
1 photo transistor (2 connection legs)
1 NTC 10 kOhm
1 Piezo speaker
1 potentiometer 10 kOhm with red dial switch

GETTING TO KNOW THE
MODULE

This first chapter is about the general functions of the WLAN-modules. The mod­ule is controlled with AT commands. All example programs shown here, help and
further information can be found at www.iot.fkainka.de

It is easiest to download the entire ZIP directory and copy the unpacked folder into
your sketch folder completely. Then you can open all programs comfortably in
sequence from the Arduino interface.

1.1

|

Basic AT commands

For a first impression how to use the AT-commands, best just try them out. There­fore, this section will introduce you to some of the basic commands for the module.

For this, open the program P01_SoftwareSerial in the Arduino-IDE. This is a
very simple program that does nothing but pass on all data received via the serial

hardware interface of the micro controller to the ESP controller via a self-defined
software interface. The entire thing works in the opposite direction as well. As you
can see in the source text, the two connections of the software interface are pins
11 and 12. They should not be used as GPIO-pins in your own projects. You also
need the SoftwareSerial-Library that is pre-installed already in most Arduino
versions – if not, download the library via the manager.

After the program has been uploaded, you can start the serial monitor of the Ardu­ino interface. Before you can start, two important settings must be made to the
Serial Monitor, i.e. the baud rate must be set to 19200 in the lower right corner

and the setting CR and NL must be made in the box to its left.

Now you can see a message, i.e. AT and a few lines below OK. The command

AT was sent to the ESP module by the micro controller and the module answered
OK. You can see by this that the WLAN module works and is ready for use.

Terminal settings: CR and NL and a Baud rate of 19200

1.1.1 | Basic commands

You can now try out some basic commands of the module by simply entering the
command and sending it to the module with

[Enter]

. Capitalisation of the com-

mand is important. You can submit the first command of your own by entering

AT

in the serial monitor and pressing

[Enter]

. The uploaded program passes on the
command to the ESP module, which in turn answers AT and then OK. The next
command that you can test is:

AT+GMR

This command outputs the current firmware and version number.
The command

AT+RST

resets the module. You will see a few illegible characters on the terminal first,
followed by ready, which says that the module is now ready. Another command is:

ATE0

This permits deactivating the echo of the module. This means that the command
you sent will not be returned, but only the answer will be. For example, if you send
AT, the response will not be AT and then OK, but only OK. However, for your first
attempts, it is recommended to reactivate the echo with

ATE1

.

First attempts with the AT-commands

1.1.2 | WLAN-commands

The following WLAN-commands can be used to change the WLAN properties of
the module. Some commands not only permit specification of a condition, but also
requesting the current condition. This is done by entering a question mark after the
command, e.g.

AT+CWMODE?

The returned value usually will be

+CWMODE=2

followed by OK. If you enter

AT+CWMODE=?

, the module will answer with the possible parameters for the command, in this
case 1-3. CWMODE is a command that you can use to specify the WLAN-mode,
by the way.

There are therefore three operating modes that I will explain below.

1

AT+CWMODE=2 – the module as Access Point (AP-mode)

In the delivery condition, the module is an Access Point. This means that you can
directly connect to the module with a WLAN-capable device, such as a smartphone
or a PC. For this, simply find the open WLAN with the name NanoESP and connect
to it. In the default condition, no password is assigned, so that connection is not a
problem. If you are connected to the module, you have no connection to the internet,
since the module is not a router with a dedicated connection to the phone network.
This WLAN-mode is still sensible, however, for example if you need a closed, safe
network. Speaking of safety: There is also the option of assigning a password to the
network, using the command:

AT+CWSAP

You need to enter parameters in the following order and separated with a comma:

U

the name of the network in quotation marks,

U

the password in quotation marks,

U

the channel ID (any value between 1 and 13),

U

and the encryption mode (value from 0-4).

One possible setting would be:

AT+CWSAP="MyNanoESP", "MyPassword", 5,3

After a short period, OK appears as confirmation. If an ERROR appears, check
your input again, and in particular check the quotation marks. If an ERROR ap­pears anyway, check that the CWMODE is actually set to 2.

If everything works, you can connect to the board with a WLAN-capable device. All
devices connected to the module can be displayed with IP and MAC addresses
with the command

AT+CWLIF

.

The module in station mode. The IP of the connected computer is highlighted.

2

AT+CWMODE=1 – the module in station mode

The command

AT+CWMODE=1

sets the module to station mode. This mode permits connecting to your WLAN­router. This will also connect the module to the Internet and give it a lot more op­tions.

You can first use the command

AT+CWLAP

to list all networks in range to check if your network is within reception range. To
connect to your router, you need the command

AT+CWJAP

Similar to the CWSAP-command, this has important parameters, i.e. the name of
the WLAN-network (also called the SSID) and the password, each again in quota­tion marks and separated by a comma. Connecting to a second module that is set
with the data according to the previous section would look as follows:

AT+CWJAP="MyNanoESP", "MyPassword"

It may take a few seconds to establish the connection. Then OK should be re­turned. You can call the IP of the module that the router assigns with the com­mand

AT+CIFSR

. This will be important later when you want to connect to the TCP-server of the
module. The command

AT+CWQAP

will disconnect the connection with your router again.

The board connects to a second NanoESP.

3

AT+CWMODE=3 – dual mode

The third possible mode for the WLAN setting is dual mode. As the name sug­gests, it permits operating the module in station and AP-mode. This means that
devices can establish a direct WLAN connection to the module, or reach the mod­ule through the router as an interim station. It is a practical mode, e.g. when you

are planning an internal network with several
modules, but want one module to serve as the
server that supplies all data to the network. We
will get back to this later.

1.2 | Automatic configuration

The basic commands can be tested manually already. This chapter is to explain

how the commands can be automatically operated via the controller. You will also
learn another command that you can use to test if a computer in the network or a
server online can be reached. In this example, the Google server will be pinged.
The example program P02_GooglePing mostly automates the processes that you
entered manually in the first example. The controller sends commands to the ESP
module in sequence, thus connecting to the WLAN, among others. The differently
long time-out times give the module enough time to answer.

Before the program can work properly, you need to enter your WLAN data after #de­fine SSID and #define PASSWORD right at the beginning of the program source code.
The module needs access to the Internet to execute its last command. The command

AT+PING

pings other devices in the network. Pinging means a query whether a computer
can generally be reached. Here, the Google server is pinged with
AT+PING="www.google.de". When a response returns, a success message ap­pears on the serial monitor and the LED labelled D3 that is connected to pin D13
at the board is activated. The first communication with the Internet is successful.

The program

We will analyse the program functions step by step below. First, we will cover com­munication with the module.

1

Serial communication

This works via the serial software interface that is provided with the Software­Serial-Library. When initialising, you also need to indicate the pins used: in this
case these are pins 11 and 12.

001

#include <SoftwareSerial.h>

002

SoftwareSerial esp8266(11, 12);

Just as for the normal serial interface, you can then transfer bytes or entire lines
with the commands esp8266.print or esp8266.println. The commands
esp8266.find and esp8266.findUntil, with which an incoming stream can be
checked for specific character strings, are particularly useful as well. This makes it
rather simple to catch the matching response from the module. However, if an
expected character string does not appear, it may take a while until the program
continues. The waiting time (time-out) is defined byesp8266.setTimeout. findUntil()
can also be used to define a second character spring in which the search function
stops and returns false as the return value. We will use this in the function send­Com():

001

//-------Controll ESP--------

002

003

boolean sendCom(String command, char respond[])

004

{

005

esp8266.println(command);

006

if (esp8266.findUntil(respond, "ERROR"))

007

{

008

return true;

009

}

010

else

011

{

012

debug("ESP SEND ERROR: " + command);

013

return false;

014

}

015

}

When you call the function, you therefore need to submit the command and the
expected return value to the function, e.g. AT and the expected return value OK.
println() transmits the command and finally waits until the expected return value or
an ERROR is received. When the expectation is met, the function returns the val­ue true. Otherwise, the module will use the debug()-function to return an ESP
SEND ERROR and the sent command, so that it is easy to check which command
caused the problem.

Not all AT-commands have a unique or one-line return value. If, e.g., the IP ad­dress is queried, there usually is no previously known value. Therefore, a second
sendCom()-function exists that only needs the parameter command and will then
return the entire received string. The string should not be too long, since the buffer
of SoftwareSerial can overflow.

001

String sendCom(String command)

002

{

003

esp8266.println(command);

004

return esp8266.readString();

005

}

2

Troubleshooting

There will often be errors and complication when developing programs. To have
any chance at all at finding them, there are two debug-functions that are activated
or deactivated via a parameter at the very beginning of the program.

#define DEBUG true

The first function does nothing but provide a simplified output of text via the serial
interface defined as standard. When the constant DEBUG is true, the content of
the string Msg will be sent.

001

void debug(String Msg)

002

{

003

if (DEBUG)

004

{

005

Serial.println(Msg);

006

}

007

}

The second function is also explained quickly. When the function
serialDebug is called, the program will switch to a permanent loop and will from
then onwards behave like the first tested SoftwareSerial-program. This means that
all data that are sent to the controller via the serial monitor will be passed on di­rectly to the module and vice versa. In case of error, you can therefore call the
function and send manual commands to see where the error is located.

001

//---Debug Functions---

002

void serialDebug() {

003

while (true)

004

{

005

if (esp8266.available())

006

Serial.write(esp8266.read());

007

if (Serial.available())

008

esp8266.write(Serial.read());

009

}

010

}

3

Configuration

To improve overview of the programs in general, most settings have also been
removed into individual functions, first of all the function espConfig, in which the
most important parameters for the respective program are set.

001

//---Config ESP8266---

002

boolean espConfig()

003

{

004

boolean success = true;

005

esp8266.setTimeout(5000);

006

success &= sendCom("AT+RST", "ready");

007

esp8266.setTimeout(1000);

008

009

if (configStation(SSID, PASSWORD)) {

010

success &= true;

011

debug("WLAN Connected");

012

debug("My IP is:");

013

debug(sendCom("AT+CIFSR"));

014

}

015

else

016

{

017

success &= false;

018

}

019

020

success &= sendCom("AT+CIPMODE=0", "OK");

021

success &= sendCom("AT+CIPMUX=0", "OK");

022

023

return success;

024

}

At the beginning of the function, the variable success is set to true first, since this
variable is now and-linked to various functions. This means that even if only one of
the functions that have the value returns false, success will also immediately be­come false and the entire configuration will have failed. The first AT-command to
be reviewed for success this way is the Reset-command, which is nearly always
performed at the beginning of the program to ensure that prior tests are not still
using the module. However, it may take up to five seconds until the module returns
the message ready. Therefore, the time-out for esp8266.findUtil is increased just
before thesendCom()-function. After the reset, the time-out is returned to the stan­dard value of one second.

This is followed by calling a self-defined function called configStation(), which will
be discussed in the next section. It is used to connect the module to your home
network. For this, the parameters SSID and PASSWORD will be transmitted that
you entered at the beginning of the program. If the connection has been success­fully established, the success message and then the current IP of the module are
transferred to the serial monitor. At the end of the function, parameters will be set
that I will deal with later. Last, the variable success will be returned, which hope­fully has kept the value true.

001

boolean configStation(String vSSID, String vPASSWORT)

002

{

003

boolean success = true;

004

success &= (sendCom("AT+CWMODE=1", "OK"));

005

esp8266.setTimeout(20000);

006

success &= (sendCom("AT+CWJAP=\"" + String(vSSID) + "\",\""
+ String(vPASSWORT) + "\"", "OK"));

007

esp8266.setTimeout(1000);

008

return success;

009

}

The function configStation() has been called in the espConfig()-function. Here,
setting of the WLAN-mode to station mode with the command CWMODE and then
connection to the network via the CWJAP-command are performed. It can take
quite a long time until the connection is established. Therefore, the time-out is
briefly raised to 20 seconds here. If you prefer dual WLAN-mode, you can set
CWMODE to 3 here.

001

boolean configAP()

002

{

003

boolean success = true;

004

005

success &= (sendCom("AT+CWMODE=2", "OK"));

006

success &= (sendCom("AT+CWSAP=\"NanoESP\",\"\",5,0",
"OK"));

007

008

return success;

009

}

The function configAP() is not called here, but should be mentioned briefly any­way. It is the counterpart to the configStation()-function, since it is used to set the
module to Access Point. A long time-out is not necessary here, since the module
can process the CWSAP-command much faster. In later tests, the espConfig()­function instead of the
configStation() will be used to call the configAP()-function.

001

void setup()

002

{

003

// Open serial communications and wait for port to open:

004

Serial.begin(19200);

005

// set the data rate for the SoftwareSerial port

006

esp8266.begin(19200);

007

008

if (!espConfig()) serialDebug();

009

else debug("Config OK");

010

011

if (sendCom("AT+PING=\"www.google.de\"", "OK"))

012

{

013

Serial.println("Ping OK");

014

digitalWrite(13, HIGH);

015

}

016

else

017

{

018

Serial.println("Ping Error");

019

}

020

}

021

022

void loop() // run over and over

023

{

024

//Start serial Debug Mode - Type commands over serial Monitor

025

serialDebug();

026

}

The most important functions that you will find in nearly every program have now
been covered. These functions will now be used in the known Arduino functions
setup() and loop(). First, however, the two serial interfaces with 19200 Baud will be
initialised. Only then will the function espConfig() be called. In case of error, the
serialDebug()-function will be started at once. If everything went well, a success
message is sent. In later programs, the LED at Pin 13 that is marked with D3 on

the board will also light up after successful configuration. This also gives you feed­back when the module is not connected to a PC with serial monitor. In this experi­ment, however, the LED is needed for the feedback of the ping status. The query
takes place right in the next line of the configuration, too. The AT+PING-command
will be sent with the Google address as a parameter. You can query an IP address
from your local network instead of this address as well. In case of success, a mes­sage will appear and the LED D3 as mentioned will be activated. As the last ac­tion, the program will jump to the loop-function, which in turn will call the serialDe­bug()-function. You can therefore, test further commands after the program and
thus ping, e.g., further addresses.

1.3 | Recognition of a network

This chapter is, among others, about a smaller hardware setup for the first time.
The target of the project is a kind of alarm system that will react when a specific
network comes into range or is switched on.

Only two parts and some wire are used. The pre­cise setup can be taken from the setup images.

Connection of the Piezo speaker

The source text for this project differs from the previous experiment mostly in the
following functions:

001

void findSSID()

002

{

003

esp8266.println("AT+CWLAP");

004

if (esp8266.findUntil(ToFindSSID,"OK")) alarm();

005

else debug("SSID not found!");

006

}

007

008

void alarm()

009

{

010

debug("alarm!");

011

012

digitalWrite(LED_ALARM, HIGH);

013

014

for (int i; i <=30; i++)

015

{

016

tone(PIEZO, 400, 500);

017

delay(500);

018

tone(PIEZO, 800, 500);

019

delay(500);

020

}

021

022

digitalWrite(LED_ALARM, LOW);

023

}

The function findSSID() is called about every 30 seconds in the loop-routine and

will then scan for all networks in the environment. When the network you are look­ing for has been found, the function alarm() will be tripped, which switches on the
LED D3 and emits a signal sound at the piezo. In the example program, we scan
for a network with the SSID NanoESP, i.e. actually other NanoESP-networks in
range. You can also enter another SSID in #define ToFindSSID at the beginning of
the program. Then you can check, for example, how far your WLAN-network goes.

UDP AND IP

This chapter covers general data exchange between two systems via a WLAN­network. We will deal with subjects such as IP, ports and the UDP protocol. First,
let us explain these basic terms.

What is an IP-address?

An IP-address works like a postal address. It can be used to clearly identify and
address a computer in the network. An IP-address according to the still-common
IPv4-standard looks as follows:

192.168.4.1

These are four numbers, or rather four bytes. This means that the value of each
number cannot exceed 255. Generally, there are local IP-addresses, i.e. IPs that
are assigned, e.g., to the computers and devices in your home network, and global
IPs.

Local IPs are usually assigned by your router. They usually start 192.168. The
following number differs from router to router. If the NanoESP acts as Access
Point and computers can connect to its network, PCs will receive an address that
starts with 192.168.4. This opens a subnetwork at the same time. Fritz!Box routers
usually assign local IP-addresses according to the structure 192.168.178.X. You
can find out your IP by entering, e.g. the command ipconfig in the Windows com-

mand prompt (under Start -> Programs -> Accessories -> Prompt ). A longer list
will appear, which includes, among others, the item IPv4-address with your local
IP in the network.

Global IPs are usually assigned by your internet service provider. This is, e.g., the
address via which your router can be reached in the global network. The router
opens the local network and distributes the data to the clients. One way of finding
out your global IP is calling the website http://www.meine-aktuelle-ip.de/. That

website shows further data that can be viewed by a web server as well. You are
not as anonymous online as you may think.

What is a port?

When comparing to a postal address, the port would be similar to the front door in
an apartment house. A computer with a unique IP can provide different services
via different ports. You can reach the server via the IP, but you use the port to
choose the service to be used. For example, this can be port 20 for FTP data
transmission or port 23 for a Telnet connection. You can usually select the port
freely; however, there are standardised ports that make handling web applications
easier. A list of standardised ports can be found at

https://de.wikipedia.org/wiki/Liste_der_standardisierten_Ports

What is UDP?

UDP is short for User Datagram Protocol. This is a minimal, connection-free net­work protocol. Generally, it is more minimalist and simpler than other internet pro­tocols, such as TCP, which we will deal with later. The comparison is not particu­larly simple here yet, but you may remember the following regarding the protocol's
properties:

U

UDP is broadcast-capable.

U

It does not review the data for accuracy or correct errors.

U

There is therefore no guarantee that data have been successfully

transmitted.

U

There also is no guarantee that data have not been falsified on the

way or listened in on by third parties.

U

You do not need to establish a connection first. Quick data exchange

is possible.

U

There are barely any transmission delay fluctuations.

U

The format is suitable, e.g., for VoIP (Voice over IP – i.e. phone calls

via internet).

These are the most important basics on the terms for the following projects. The
subject can be dealt with in more detail still, and further information will follow in a
suitable location. First, let us deal with the practical part.

2.1 | Exchanging data between the board und PC by UDP

In this project on the subject of UDP, data are exchanged between the board and
the PC via the WLAN. The prerequisite for this is that your computer has a WLAN
adapter. A program on the PC-side ensures successful receipt of the messages.
You will not need any special hardware setup for this experiment.

The program

When you load the program P04_UDPBasics.ino onto the controller, the controller

is configured as an access point and you can see an open network called
NanoESP NanoESP. Before connecting to the network, first download a program
from the Internet. In my experiments, I used the program Packet Sender by Dan
Nagle which you can download from the following link:

https://packetsender.com/
After loading and installing the program, you can connect your PC to the open

network of the NanoESP. Ensure that the firewall recognises the network as a
home network, to avoid blocking data. Your computer should now have the IP

192.168.4.2. You can check this by sending the command

AT+CWLIF

to the module via the serial monitor. This command shows all computers con­nected to the access point with IP and MAC addresses.

Start the program Packet Sender, set the UDP server port to 90 in Settings ->
Network and click the checkbox Enable UDP Server. In Usually, the lower left
should say UDP:90. If it does not, you need to restart the software once.

The proper settings in the program Packet Sender

The program on the computer is now used as UDP server, while the controller is

set as UDP client. The differentiation between client and server is not clear in the
UDP protocol, but in this case it means that you will send data from your controller
to the computer.

The message
has been successfully transmitted.

To send data, use the command:

AT+CIPSEND=7

The 7 means the number of characters to be sent. The character > is returned.
This means that you can now send your message. Enter Hello and confirm with

[Enter]

again. The module returns SEND OK, although you have only entered
five characters. This is because after your input, Carriage Return and New Line
are sent as well, i.e. two characters more that you need to include in your mes­sage length calculation.

When you switch back to the Packet Sender and look at Traffic Log there, you can
see the receipt of the message. In the ASCII view, you will even see the two en­closed characters, represented by \r and \n.

The message has been received by Packet Sender.

001

boolean configUDP()

002

{

003

boolean success = true;

004

005

success &= (sendCom("AT+CIPMODE=0", "OK"));

006

success &= (sendCom("AT+CIPMUX=0", "OK"));

007

success &=
sendCom("AT+CIPSTART=\"UDP\",\"192.168.4.2\",90", "OK");
//UDP-Server

008

return success;

009

}

In the Arduino program, the function configUDP() is particularly decisive for the
communication path. The settings important for transmission are made there. First,
use CIPMODE to set the data transparency mode to 0. Finally, use CIPMUX=0 to
set that only one single connection is permitted. The decisive command is CIP­START. It is used to establish a commutation, specifically to IP 192.168.4.2, i.e. to
your PC, and to PORT 90, where the program Packet Sender is listening with its
UDP-server. These are the steps that are initially necessary to establish the first
communication.

2.2 | Sending and receiving data with UDP

In the preceding project, the UDP communication was tested in one direction, i.e.
from the board to the PC. In this program, the module is set so that communication
in the other direction is possible as well, almost like in a chat.

The program

This program generally only contains a very small change that has a great effect
on the communication with the UDP protocol. When you upload the program, an­other access point with which you can connect to a PC is generated. Again, you
will need Packet Sender or a comparable program. Start the program and make
the same settings as before (File -> Settings -> Network: Enable UDP Server, Port

90). Then you need to enter the address of the module in the main window in the
IP Address field (192.168.4.1), set the Port to 91 and select the item UDP in the
dropdown menu farther to the right. When these settings have been made and the
serial monitor has been opened, you can send the first message to the module by
entering, e.g., Hi in the field labelled ASCII.

If you click Send now, the Serial Monitor will show:

001

+IPD,2:Hi

002

OK

The Packet Sender has successfully submitted »Hi«.

The message has been received. You can answer by using the CIPSEND com­mand again, i.e. for example:

001

AT+CIPSEND=7

002

>Hello

The difference from the previous program is only in a single line:

success &= sendCom("AT+CIPSTART=\"UDP\",\"192.168.4.2
\",90,91", "OK");

As you can see, a second port was indicated. This port, here the one with number
91, is the port through which the module listens for incoming data in turn. By attach-