Parts List. XBEE/Wifi Adapter board 4 standoffs ¼ inch screws Cable XBEE module or Wifi module

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Daniela Lang
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1 Rover Wifi Module 1

2 Legal Stuff Stensat Group LLC assumes no responsibility and/or liability for the use of the kit and documentation. There is a 90 day warranty for the Sten-Bot kit against component defects. Damage caused by the user or owner is not covered. Warranty does not cover such things as over tightening nuts on standoffs to the point of breaking off the standoff threads, breaking wires off the motors, causing shorts to damage components, powering the motor driver backwards, plugging the power input into an AC outlet, applying more than 12 volts to the power input, dropping the kit, kicking the kit, throwing the kit in fits of rage, unforseen damage caused by the user/owner or any other method of destruction. If you do cause damage, we can sell you replacement parts or you can get most replacement parts from online hardware distributors. If you need to contact us, go to and click on contact us. 2

3 Parts List XBEE/Wifi Adapter board 4 standoffs ¼ inch screws Cable XBEE module or Wifi module 3

4 Introduction The wifi module adds a way to communicate with the rover kit. You can connect using a laptop. For the rover, the wifi module will be configured as an access point. This means it becomes a local network where your laptop connects. It is also possible to have a tablet connect to the rover. In this lesson, you will learn how to control the rover and have the rover send data back. This will require you to write code on the laptop. 4

Control Program The control program sends commands over the wifi to the rover.

5 System Architecture This drawing shows how everything is interconnected. The control program runs on the laptop. The laptop wifi connects to the rover wifi module. Control Program The control program sends commands over the wifi to the rover. The arduino program on the rover interprets the commands and executes them. wireless link The arduino program on the rover also sends telemetry over the wifi to the control program on the laptop. Arduino rover Program 5

6 What is the Plan In this lesson, you will learn how to program the rover to set up the WiFi module as an access point and receive commands to move from your computer. You will also learn how to send telemetry back to the computer. We will use the light sensor and infrared proximity sensor for telemetry. Telemetry is the transmission of data or information. 6

7 What is Wifi WiFi is a local area wireless computer network. It is also known as wireless local area network. WiFI is a standard for allowing computers to interact with each other using radio signals. A wireless access point is a device that connects a wireless network to a wired network. It can also provide a local isolated network not connected to the internet or other wired network. Access points usually have a network router and can provide network addresses or IP addresses to any device that connects. 7

8 Wifi Terms SSID is a unique identifier for the WiFi network. It can have up to 32 characters and is case sensitive. This allows multiple WiFi access points in the same area without interfering with each other. IP Address is the internet protocol address assigned to each device on the network. There are two standards, IP-4 and IP-6. IP-4 is used here. The address consists of four sets of numbers separated by a decimal point. Each number has a range of 0 to 255. Example DHCP is Dynamic Host Configuration Protocol. This protocol allows a WiFi router to assign an IP address to any device that connects to the WiFi network. This is done automatically. TCP is Transmission Control Protocol. This is one of the main network protocols used by any device on any WiFi network or the internet. The protocol enables two devices to establish a connection to each other and exchange data. The protocol guarantees delivery of data and that the data is delivered in the same order sent. 8

9 Wifi Module Installation Install the four standoffs by screwing them into the screws holding the processor board. 9

10 Wifi Module Installation Mount the wifi module on top of the standoffs. Make sure to orient the wifi module. This will let the cable harness reach. Secure the wifi module with four nuts. 10

11 Wifi Module Installation Connect the cable harness to the wifi module and the UART port. Connect the pin marked + on the processor board to the pin marked + on the wifi module. Connect the pin marked on the processor board to the pin marked on the WiFi module. Connect the pin marked T on the processor board to the pin marked R on the wifi module. Connect the pin marked R on the processor board to the pin marked T on the wifi module. 11

12 Wifi Module Signals The power connections between the processor board and the wifi module provide the wifi module with 5 volts of power. For communications, the processor board T or transmit signal is connected to the wifi module R or receive signal and vice versa. Transmit is the sending of information and Receive is the reception of information. 12

13 WIFI Module Operation There are two parts to the WIFI module operation Configuration which sets up the module to operate properly Data operation where the module receives data and can send data The WIFI module will be configured to operate as an access point. This allows another computer to connect to the module and communicate with the module. More than one WIFI module can be in the same area and operate independent of each other as long as their SSID are different. In this lesson, the WIFI module will be configured as an access point and allow TCP connections. 13

14 Wifi Configuration There is a library for the rover to initialize the WiFi module and control the rover. First, import the library called Stensat Group Rover Library Then create a rover object with the statement Stensat_Rover rover; #include <stensat_rover.h> Stensat_Rover rover; void setup() Serial.begin(9600); void loop() 14

15 Wifi Configuration In the setup() function, the WiFi is initialized with the init_wifi() function. The init_wifi() function takes two arguments. The first argument is the SSID which can be any name. Double quotes must be used around the SSID name. The second argument is the port number which is set to 80. It can range from anywhere from 1 to #include <stensat_rover.h> Stensat_Rover rover; void setup() Serial.begin(9600); rover.init_wifi( robot,80); void loop() 15

16 Wifi Configuration Upload the program and let it run on the processor. Be sure to disconnect the WiFi module before uploading. The WiFi module uses the same UART interface that the USB port does. Having the wifi module connected will keep the program from uploading. Once uploaded, turn off the rover and connect the wifi module. void #include setup() <stensat_rover.h> Stensat_Rover Serial.begin(9600); rover; delay(200); void Serial.println( AT+CWMODE=3 ); setup() delay(200); Serial.println( AT+CWSAP=\ robot1\,\ \,1,0 ); Serial.begin(9600); delay(1000); rover.init_wifi( robot,80); Serial.println("AT+CIPMUX=1"); delay(200); void Serial.println("AT+CIPSERVER=1,80"); loop() void loop() Turn on the rover and wait a couple minutes. On the laptop check for the access point you named. Try connecting to it. 16

17 Programming the rover Now that the wifi module is working, it is time to program the rover to receive commands and perform actions. Commands need to be created for the rover to interpret and act on. The following actions need commands: Forward Reverse Left Right Stop The commands are shown in the table to the right. The actions of the rover are simple, a simple 1 character command will be used. Action Stop Forward Reverse Left Right Command S F B L R The command will be terminated with a carriage return. The carriage return is represented by '\r'. 17

18 Configuring the rover After configuring the wifi, the rest of the rover needs to be configured. The rover.begin() function configures the four digital pins used to control the motors as outputs. #include <stensat_rover.h> Stensat_Rover rover; void setup() Serial.begin(9600); rover.init_wifi( robot,80); rover.begin(); void loop() 18

19 Receiving Commands The wifi module has a specific format for passing on received information. The format is shown below The first part is called the header. It identifies that it is sending information received from another computer that is connected to the wifi module. The second part is the information or data that was sent to the wifi module. The third part is the terminator indicating end of information. +IPD,0,x:informationhere<0x0d><0x0a>OK<0x0d><0x0a> 19

20 Receiving Commands In the loop() function, a character array is created to receive commands. The first thing to do is wait for any data to come from the wifi module. The wifi module has a specific format for data received. The data to be received are the commands to operate the rover. void loop() char cmd[10]; if(serial.available() > 0) int err = Serial.find( +IPD ); The Serial.available() function is used to detect any data available from the wifi module. It returns a value of 0 if there are no bytes. 20

21 Receiving Commands The function Serial.find() is useful in finding text patterns received through the serial interface. The pattern being searched is +IPD. This function will look for the pattern for up to two seconds. The variable err is set based on the results of the function. void loop() char cmd[10]; if(serial.available() > 0) int err = Serial.find( +IPD ); If the Serial.find() function detects the pattern, it will set the variable err to 1 or TRUE. If after a second, the pattern is not detected, the result will be 0 or FALSE. 21

22 Receiving Commands Only when the result is TRUE should any processing occur. The next Serial.find() function looks for the colon character. This lets the program easily find where the command starts. After locating the colon, the rest of the data is copied into the variable array buf[]. void loop() char buf[100]; if(serial.available() > 0) int err = Serial.find( +IPD ); if(err == TRUE) Serial.find( : ); i = Serial.readBytesUntil(0x0a,buf,100); 22

23 Receiving Commands Serial.readBytesUntil() function copies anything on the serial interface to an array buffer until the character value hexadecimal 0x0d is encountered. Remember the information is terminated with hex value 0x0d and 0x0a. Just looking for 0x0a is enough to stop copying data into the array buffer. void loop() char buf[100]; if(serial.available() > 0) int err = Serial.find( +IPD ); if(err == TRUE) Serial.find( : ); i = Serial.readBytesUntil(0x0a,buf,100); 23

24 Receiving Commands The first element in the array buffer is the command. This is compared in the switch function. The switch() function behaves like a series of if() statements but has simpler syntax. The case statement is what compares the variable buf[0] with what is in single quotes. If the comparison is valid, the code after the colon will be executed. void loop() char buf[100]; if(serial.available() > 0) int err = Serial.find( +IPD ); if(err == TRUE) Serial.find( : ); i = Serial.readBytesUntil(0x0a,buf,100); switch(buf[0]) case 'F' : forward(); break; case 'B' : reverse(); break; case 'L' : left(); break; case 'R' : right(); break; case 'S' : halt(); break; 24

25 Receiving Commands Notice the break statement. This is needed to stop the execution of code. If it is not included, the program would continue executing the code in each case statement below the initial case statement. void loop() char buf[100]; if(serial.available() > 0) int err = Serial.find( +IPD ); if(err == TRUE) Serial.find( : ); i = Serial.readBytesUntil(0x0a,buf,100); switch(buf[0]) case 'F' : forward(); break; case 'B' : reverse(); break; case 'L' : left(); break; case 'R' : right(); break; case 'S' : halt(); break; 25

26 Remote Control Software With the rover software completed, it is time to write a program on the laptop to provide the control. Processing software will be used. 26

Software Development The development software to be used is called Processing. Processing Is a programming language and development environment using Java.

27 Software Development The development software to be used is called Processing. Processing Is a programming language and development environment using Java. Processing makes developing software easier. More information can be found at processing.org. The software is free to download and use. The development environment is similar to the Arduino development environment. 27

28 Software Development Sequence The program to be written will allow the rover to be controlled with the arrow keys on the keyboard. The program must detect when an arrow key is pressed and when it is released. Key pressed? When the key is pressed, a command will be sent to the rover. When the key is released, the stop command will be sent. Key Released? Send Stop Command Send Forward Command Send Reverse Command UP DOWN Send Left Command Determine Which Key Pressed LEFT RIGHT Send Right Command 28

29 Importing Libraries Start the Processing software. Click on the Sketch menu and select the Import Library import processing.net.*; Select the net library. The import command will appear at the top of the editor. This tells the compiler to include the library of functions to support network operations. This library will be used to access the rover over wifi. 29

30 Setting up a TCP Port The next step is to create a network object that will provide access to the wifi. import processing.net.*; Client c; 30

31 Setting up a TCP Port In the setup() function, the network object is configured to talk to the rover at the IP address of using port 80. A window of 800 by 600 pixels is also created. import processing.net.*; Client c; void setup() size(800,600); c = new Client(this, ,80); 31

32 Detecting the Keys To detect the keys, two event functions will be used. keypressed() and keyreleased() keypressed() is executed when a key on the keyboard is pressed. keycode is a system defined variable that tells you what key was pressed. The arrow keys have names in upper case to make it easier to use. import processing.net.*; Client c; void setup() size(800,600); c = new Client(this, ,80); void keypressed() if(keycode == UP) c.write( F ); else if(keycode == LEFT) c.write( L ); else if(keycode == RIGHT) c.write( R ); else if(keycode == DOWN) c.write( B ); 32

33 Detecting the Keys Notice that the network object c has a function called write(). This sends what is in quotes to the rover over wifi. For this to work, Processing requires the function draw() to exist even if there is no code in the function. import processing.net.*; Client c; void setup() size(800,600); c = new Client(this, ,80); void keypressed() if(keycode == UP) c.write( F ); else if(keycode == LEFT) c.write( L ); else if(keycode == RIGHT) c.write( R ); else if(keycode == DOWN) c.write( B ); void draw() 33

34 Detecting Key Release The code can now send commands to control the motion of the rover. What is missing is a way to stop the motion of the rover. The keyrelease() function is executed when a key is released. The only thing the function needs to do is send the stop command to the rover. A single c.write() function is used. The first argument has the S command. Remember the rover commands are terminated with a linefeed. import processing.net.*; Client c; void setup() size(800,600); c = new Client(this, ,80); void keypressed() if(keycode == UP) c.write( F ); else if(keycode == LEFT) c.write( L ); else if(keycode == RIGHT) c.write( R ); else if(keycode == DOWN) c.write( B ); void keyreleased() c.write( S ); void draw() 34

35 Test Drive Now that the program is completed, it is time to test it. Turn on the rover with the wifi module connected. on the laptop, select the network icon to find available wifi access points. Connect the laptop to the rover wifi network. Start the program in Processing. Press the arrow keys and watch the rover move around. When the program starts, a window will open. This is the program running. If needed, click on the window to make it active. If at first the laptop doesn't connect properly to the rover WiFi access point, cycle power to the rover and wait 30 seconds for the WiFi to start up and try connecting again. Some times the WiFi module does not quite work the first time it is programmed. 35

36 Wifi Module Schematic 36

Parts List. XBEE/Wifi Adapter board 4 standoffs ¼ inch screws Cable XBEE module or Wifi module

Parts List. XBEE/Wifi Adapter board 4 standoffs ¼ inch screws Cable XBEE module or Wifi module Rover Wifi Module 1 Legal Stuff Stensat Group LLC assumes no responsibility and/or liability for the use of the kit and documentation. There is a 90 day warranty for the Sten-Bot kit against component