Bouncing virtual ball with Arduino (and Blender)

UPDATED 20.4.2009

I'm quite new on this Arduino stuff and I may have misunderstood something. But anyway, here are some observations of using Arduino and Blender's game engine.

It's easy!

It is really easy to get values from Arduino to Blender. Here is a simple setup for reading photo-resistor's values from Blender:

from Blender.Mathutils import Vector import serial 
port = '/dev/ttyUSB0' 
pin = 0 
try: 
    GameLogic.SerialPort 
except: 
    GameLogic.SerialPort = serial.Serial(port,9600) 

# read data 
valo = GameLogic.SerialPort.readline() 
val = float(valo)/200 

# BLENDER stuff 

objs = GameLogic.getCurrentScene().getObjectList() 
cube = objs["OBbox"] 
cube.setPosition([1.0,1.0,val])

Here I'm reading photoresistor values and then tell Blender's game-engine to change "box" object's position according that value. The arduino code looks like this:

/* Arduino reading photo resistor to serial * * */ 
int analogPin=0; 
int analogVal=0; 
void setup() { Serial.begin(9600); } 
void loop() { 
    // get the value from photoresistor 
    analogVal = analogRead(analogPin); 
    Serial.println(analogVal); 
    //delay(100);
}

Not so fast!

There is a one catch when reading data from Arduino to Blender. And that's the fact that python scripts are executed on every frame and that mean that you'll read data from serial port approx. 60 times per second.

However, Arduino is sending data much faster. As a result, you'll see a horrible delay in Blender. That's because the data arduino sent is buffered and you are actually reading from buffer. So you'll get "historical" values from serial port, not the current values. And for interactive application that is not wanted.

There are couple of ways to fix this:

The simplest way is to program Arduino to send data more rarely. You could use delay function if there is nothing else that Arduino should do (delay halts everything in Arduino).

Request/response model

Better and more predictable way is to tell Arduino when we want to get a value. So when we want a value, we send a signal to arduino to send data and then we read the value. This way we'll always get the current values no matter of how high or low our frame rates are.

(I *think* that it would be also possible to run a separate python thread for Arduino input and just read values from that thread)

port = '/dev/Arduino' 
pin = 0 
 
try: 
    GameLogic.SerialPort 
except: 
    try: 
        GameLogic.SerialPort = serial.Serial(port,9600,timeout=1)  
        print 'Port ' + port + 'found!' 
         
        #ok, we have a port. Let's test if we can write to it 
        try: 
            GameLogic.SerialPort.write('x') 
            GameLogic.serialRead = False 
            GameLogic.serialOk = True 
              
        except: 
            GameLogic.serialOk = False 
            print 'could not write to port ' + port + '!' 
         
         
    except: 
        GameLogic.serialOk = False 
        print 'no port ' + port + ' found!' 
     
 
 
# do stuff if serial port is OK 
if GameLogic.serialOk: 
    if GameLogic.serialRead: 
        valo = GameLogic.SerialPort.readline() 
        val = float(valo)/100 
        GameLogic.serialRead = False     
    else: 
        GameLogic.SerialPort.write('a') 
        GameLogic.serialRead = True     
     
 
    # BLENDER stuff 
    if GameLogic.serialRead == False: 
        objs = GameLogic.getCurrentScene().getObjectList() 
        cube = objs["OBbox"] 
        cube.setPosition([1.0,1.0,val])

When Blender is ready to receive a value from Arduino, it send character "a" to the Arduino. Arduino sent one value and that is read next round. Arduino code is very simple:

int analogPin=0;
int analogVal=0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  if ( Serial.available()) {
    char ch = Serial.read();
    if ('a'==ch) {
      analogVal = analogRead(analogPin);
      Serial.println(analogVal);
    }
  }
}

Here is a very simple demo using photoresistor to control a box's position. A top of box there is a ball so you can bounce the ball with adjusting the amount of light.





That's it!