Thursday, January 21, 2010

Arduino Motion Control over Ethernet

Watching the numbers on Google Analytics definitely tells me my reading public doesn't care about my welding projects! So, let's get back to the Arduino.
When I set up to do my POP3 project, I ended up buying an Arduino Ethernet shield and an Adafruit Ethernet shield plus a Lantronix Xport. Having both, I figured it would be a good challenge to get both talking to each other and the result is this fairly simple project which actually ended up taking a lot of thought. It is loosely based on "Networked Game" project in Tom Igoe's indispensable book "Making Things Talk", but Tom's example does the much harder job of writing everything in the low-level serial commands to the Xport while I am lazy and used the published libraries! The challenge here is that the two network shields have two different Arduino libraries which really don't work quite the same way. Also, the Adafruit library is pretty light on explanation and the examples provided have no comments in the code!
Here is the basic setup of this project, basically the accelerometer on the "server" controls two servos on the "client":

The servos, of course, could be hooked up to any number of things like the X-Y axis of a camera mount or a motion base for a game of some kind. Conceptually, of course, through the magic of the Internet and with the right networking setup, the client could be in New York and the server in Instanbul. Also, through the miracle of standard IP protocols I can use one make of shield to successfully communicate with another using two totally different libraries!
Here is a quick video of the rig in action:
Note that the servos jitter slightly when they are hooked up because of slight variations of the analog readings on the accelerometer. I could probably do some averaging to smooth out the readings to eliminate that jitter.
The Server
The server is actually very simple. I used the Adafruit ADXL335 accelerometer (info) that is hooked up to the first three analog pins on the Arduino Diecimilia. The Arduino reads and sends out the X, Y and Z axis, but the client only uses the X and Y values because I only have two servos. It would be pretty easy to build support in for all three axes on the client. Apart from the accelerometer, the only other component is the LED that indicates connected or not connected.




The code is equally simple. It reads the accelerometer and when it receives a "g" from the client it prints out the X, Y & Z readings. When it receives an "x" it ends the session. That's it! Note that this uses the Ethernet.h library distributed with the Arduino software.

* Simple Ethernet Server
*
* A simple server that shows the value of the analog input pins 0 - 2 
* which are connected to an ADXL335 Accelerometer.

by Chris Armour, Jan 2010
*/

#include 

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; //Setting the MAC address
byte ip[] = { 192, 168, 0, 177 }; //IP address of the server
int XPin = 0;
int YPin = 1;
int ZPin = 2;
int ValX = 0;
int ValY = 0;
int ValZ = 0;
int ledPin = 9;
char c;

Server server(54321); //This is the port the server listens on.

//==============Setup pins, server & serial ===================//

void setup()
{
Ethernet.begin(mac, ip);
server.begin();
Serial.begin(9600);
pinMode(ledPin, OUTPUT); 
digitalWrite(ledPin, LOW);
}

//=====================Main loop =============================//

void loop()
{
digitalWrite(ledPin, LOW); //If there is no client connected the LED is off.
Client client = server.available();

while (client.connected()) {

if (client.available()) {
digitalWrite(ledPin, HIGH);  
char c = client.read(); //Read one character at a time.
Serial.print("Value received:  ");
Serial.println(c); 

if (c == 'g') { //"g means "get"
ValX = analogRead(XPin);
ValY = analogRead(YPin);
ValZ = analogRead(ZPin);
Serial.print("Value sent:  ");
Serial.print(ValX);
Serial.print(",");
Serial.print(ValY);
Serial.print(",");
Serial.println(ValZ);
client.print(">");
client.print(ValX);
client.print(",");
client.print(ValY);
client.print(",");
client.println(ValZ);
break;
}
if (c == 'x'){ //x means kill the session.
digitalWrite(ledPin, LOW); //turn off the LED
client.flush();
client.stop();
}
}
}
delay(50);
}

The Client

The client is a slightly more complex beast in that it has a switch to initiate a connection, an LED to indicate the connection state and the servos:



The code is also somewhat more involved. Part of that is because of using the AF_Xport library from Adafruit which takes a bit more fiddling, but also because the client needs the extra logic to initiate and disengage the connection. The main problem area is on resetting the Xport which doesn't always seem to want to connect on the first try so I had to build a loop in to retry the reset until it connects. This is a bit inelegant, but it looks like others have had this problem too.

/*
A network client based on Adafruit Ethernet Shield using the 
Xport ethernet-to-serial adapter. It moves servos based on analog
input from a server with an ADXL335 Accelerometer.

by Chris Armour, Jan 2010
*/

#include 
#include 
#include 
#define XPORT_RXPIN 2
#define XPORT_TXPIN 3
#define XPORT_RESETPIN 4
#define XPORT_DTRPIN 5
#define XPORT_CTSPIN 6
#define XPORT_RTSPIN 7
#define IPADDR "192.168.0.177" //IP Address of the Arduino Server
#define PORT 54321 //IP port of the server

AF_XPort xport = AF_XPort(XPORT_RXPIN, XPORT_TXPIN, XPORT_RESETPIN, XPORT_DTRPIN, XPORT_RTSPIN, XPORT_CTSPIN);

uint8_t ret; //The return variable needs to be formated as a unsigned integer of length 8 bits 
int Xval = 0;
int Yval = 0;
int Xservo = 0;
int Yservo = 0;
int buttonPin = 11;
int buttonWas = 0;
int buttonIs = 1;
int ledState = 0; //I believe these are actually flipped 0 = On 1 = off
int ledPin = 13;
boolean ConnectState = false;
char linebuffer[16]; //Very small line buffer because we just need the X-Y readings.
Servo Xservobj;
Servo Yservobj;
int loopCount = 0;

//===============Setup pins, servo, xport ==========//
void setup()  
{
 pinMode(buttonPin, INPUT);
 pinMode(ledPin, OUTPUT);
 Serial.begin(9600);
 xport.begin(9600);
 delay(300);
 Serial.println("Finished Setup...");
 Xservobj.attach(9);
 Yservobj.attach(8);
 buttonIs = digitalRead(buttonPin);
}

//===============Functions===================//

void getButton() { 
  buttonWas = buttonIs; // Set the old state of the button to be the current state since we're creating a new current state. 
  buttonIs = digitalRead(buttonPin); //Read the buttong state.
}

void errorBlink(){ //Flash 4 times for an error
     for (int x=0; x <=3; x++){  
   digitalWrite(ledPin, HIGH);  
    delay(100);  
    digitalWrite(ledPin,LOW);  
    delay(100);  
   }  
}

char * resetXport(){ //Handles the regular reset of the Xport, returns reset errors
        ret = xport.reset();
       switch (ret) {
          case  ERROR_TIMEDOUT: {
           Serial.println("Timed out on reset!");
           errorBlink();
         return 0;
      }
      case ERROR_BADRESP:  {
         Serial.println("Bad response on reset!");
         errorBlink();
         return 0;
    }
  case ERROR_NONE: {
     Serial.println("Reset OK!");
     break;
    }
    default:
      Serial.println("Unknown error");
      errorBlink();
      return 0;
       }
  delay(250);
}


char * ConnectToggle(){ //This function turns the connection on or off
  
  if (ledState == 1){ //if the LED is off, then the client is not connected.
  resetXport(); //run the reset function
  ret = xport.connect(IPADDR, PORT);
  switch (ret) { //swtich case handles various error states
    case  ERROR_TIMEDOUT: {
     Serial.println("Timed out on connect");
      ConnectState = false;
      errorBlink();
     return 0;
  }
  case ERROR_BADRESP:  {
     Serial.println("Failed to connect");
      ConnectState = false;
      loopCount++;
      Serial.print("Loop count =");
      Serial.println(loopCount);
      ConnectToggle();
      if (loopCount >  2){  //For reasons I have not been able to figure out, it usually takes two tries to connect    
         errorBlink();
         ConnectState = false;
         break;
  }
  }
  case ERROR_NONE: {
    Serial.println("Connected..."); 
    ConnectState = true;
    Serial.println(ConnectState);
    digitalWrite(ledPin, HIGH);
    ledState = 0;
    loopCount = 0;
    break;
  }
  default:
    Serial.println("Unknown error");
     ConnectState = false;
     errorBlink();
    return 0;
 }
 }
  else { //Toggle off connection
    ledState = 1;
    digitalWrite(ledPin, LOW); //turn OFF the LED
    xport.println("x"); //Send the x command that kills the session.
    delay(100); 
    xport.disconnect(); 
    Serial.println("Disconnected.");
    ConnectState = false;
  }
}

void fetchStuff() { //Gets the linebuffer
   xport.flush(100);
   xport.println("g"); 
   ret=xport.readline_timeout(linebuffer, 16, 200); // get first line
   while(ret!=0){
     ret=xport.readline_timeout(linebuffer,16,200);
  }
}

void moveServos(){ //Note that the server sends out the X, Y & Z values, but Z is not used. It could be.
   Xval = (((linebuffer[1] - 48) * 100) + ((linebuffer[2] - 48) * 10) + (linebuffer[3] - 48)); //Extract X value & convert the ASCII to integers
//  Serial.print("Xval:  ");
//  Serial.println(Xval, DEC); 
  
  Xservo = map(Xval, 275, 425, 0, 180); //Map the range of X values from the server to the servos
   Serial.print("Xservo:  ");
  Serial.println(Xservo, DEC);
  Xservobj.write(Xservo);
  delay(15);  
   
   Yval = (((linebuffer[5] - 48) * 100) + ((linebuffer[6] - 48) * 10) + (linebuffer[7] - 48));//Extract Y value & convert the ASCII to integers
//   Serial.print("Yval:  ");
//   Serial.println(Yval, DEC); 

  Yservo = map(Yval, 275, 425, 0, 180); //Map the range of Y values from the server to the servos
   Serial.print("Yservo:  ");
  Serial.println(Yservo, DEC);
  Yservobj.write(Yservo);
  delay(15);     
}
  
//==============Main loop==================//

void loop()   { // run over and over again

getButton(); //Run to check if button has been pressed.

if((buttonIs == 1) && (buttonWas == 0)){
  ConnectToggle(); //If there is a change in the button state, toggle the connection on or off.
}

if (ConnectState == true){ //If the client is connected, do some work!!
  fetchStuff();
  moveServos();
  }
}

Further work
The system needs a way to detect dropped connections - possibly using "millis()" to determine if a response or query has taken too long. As well, I really should smooth out those analog readings so the servos don't jitter! As well, I might just build a motion ase of some sort to hook up to the servos so they can do something slightly more cool that just flap their arms.
So, that's my first Arduino project in a few months! Thanks for the comments and questions. The site has apparently had over 11,000 hits, which completely amazes me. Please keep the comments and suggestions coming. I think next up will be another Chinese knock-off phone review.


12 comments:

  1. Hi, congratulations on the job, I would like, if you can rewrite the client code, but with the library ,
    thank you very much.
    Regards, Diego.

    ReplyDelete
  2. Hi Diego - Do you mean rewriting the client to use the Arduino Ethernet library instead of the AF_xport library? Good idea, but I don't have time right now and I don't have two of the Arduino Ethernet shields! :-)

    I've got a couple of other projects I'm working on right now that I will right up in a few weeks.

    ReplyDelete
  3. Yes, that was my idea, but do not worry if you feel like when you have time would be nice if you did, a greeting.

    ReplyDelete
  4. Hi, as you say "Conceptually [...] with the right networking setup, the client could be in New York and the server in Instanbul."

    To enable such a setup despite firewalls, NATs and the lack of public IPv4 addresses, we are developing a simple, open source relay server based on HTTP. For more info please visit http://yaler.org/

    Regards,
    Thomas

    ReplyDelete
  5. Hi Tamberg - Thanks for the info! I don't usually publish comments with links in them, but since this isn't spam and it looks very interesting, I will post this!!

    I will try to get to testing this out in a while. I was also looking at possible using the Twilio (www.twilio.com) to allow control via dial-in voice at some point as well.

    regards,

    Torchris

    ReplyDelete
  6. Cool, thanks for documenting! I've done something somewhat similar: http://www.tnhsmith.net/Other/Orbduino/index.htm

    Temperature is the only real "read" I have right now, but looking to add more monitoring...
    Thanks again!

    ReplyDelete
  7. Hi,

    I was trying to get your code to work on two arduino ethernet shields and was wondering how you would empliment the client code. b/c i am not having any luck.

    ReplyDelete
  8. Hi Thomas - That would take quite a bit of study to figure out and I did this almost one year ago! Maybe look at some of my other projects where I have used the Ethernet Shield and see if you can figure it out. As usual, look at the examples in the Ethernet library documentation on www.arduino.cc.

    ReplyDelete
  9. Hi I realize its been a while since you posted this project but its exactly wha I am looking for and was wondering if you have made any changes or improvements since the post in 2010?
    BTW great work!!!

    ReplyDelete
    Replies
    1. Thanks very much, fxmech! Sorry, no, I had brave intentions of doing more with this, but so far no. It would be cooler if the networking was over wifi! Best of luck with your project.

      Delete