May 29, 2009

New addition to the work bench

Thanks to Anthony from Area I.T. & T, I am now a happy owner of a dual channel 40Mhz oscilloscope.

I am happier than a pig in mud!


May 18, 2009

Sketch to calibrate SEN-08663

Got my hands on a ADJD-S371 on a breakout board from Sparkfun. The code below can be used to calibrate it. The most up-to-date version of the code can be found at my git repository under colour_sensor_calibration.

#include <Wire.h>
/* Calibrates the sensor to get white balance. Pin 2 should be connected
* to LED on the breakout board's LED pin. Calibration is done by placing the
* breakout board inside a pin pong ball, and using the built-in LED for
* illumination.
* Amount of light is measured by charging N capacitors for time X then
* reading off the voltage. (Conjecture)
* N is controlled by CAP_XXX
* T is controlled by INT_XXX
* Calibration is done by adjusting the integration time. No real reason.
int _slave_id = 0x74;
int _LED_pin = 2;

uint8_t read_register(uint8_t addr)
i2c_send(_slave_id, &addr, 1);
return i2c_read(_slave_id);

void write_register_int(uint8_t addr, int data)
write_register_multibyte(addr, (uint8_t*)&data, 2);

/* write data[i] = register+i */
void write_register_multibyte(uint8_t addr, uint8_t* data, uint8_t bytes)
for (int i = 0; i < bytes; ++i)
write_register(addr+i, data[i]);

void write_register(uint8_t addr, uint8_t data)
uint8_t bytes[] = {addr, data};
i2c_send(_slave_id, bytes, 2);

uint8_t i2c_read(uint8_t id)
Wire.requestFrom(_slave_id, 1);
for(int i = 0; i<10 && !Wire.available(); ++i, delay(10));
if (!Wire.available())
return 11;
return Wire.receive();


void i2c_send(uint8_t id, uint8_t * data, uint8_t len)
for(int i = 0; i < len; ++i)

#define CTRL 0x00
#define CONFIG 0x01

#define CAP_RED 0x06
#define CAP_GREEN 0x07
#define CAP_BLUE 0x08

#define INT_RED_LO 0x0A
#define INT_RED_HI 0x0B
#define INT_GREEN_LO 0x0C
#define INT_GREEN_HI 0x0D
#define INT_BLUE_LO 0x0E
#define INT_BLUE_HI 0x0F

#define DATA_RED_LO 0x40
#define DATA_RED_HI 0x41
#define DATA_GREEN_LO 0x42
#define DATA_GREEN_HI 0x43
#define DATA_BLUE_LO 0x44
#define DATA_BLUE_HI 0x45

int read_colour(uint8_t low_addr)
int lo = read_register(low_addr);
int hi = read_register(low_addr+1);

return lo|(hi<<8);

int red_integration_time = 2048;
int green_integration_time = 2048;
int blue_integration_time = 2048;

void set_integration_times(int red, int green, int blue)
write_register_int(INT_RED_LO, red);
write_register_int(INT_GREEN_LO, green);
write_register_int(INT_BLUE_LO, blue);

void setup()
pinMode(_LED_pin, OUTPUT);
digitalWrite(_LED_pin, HIGH);

Wire.begin(); // join i2c bus (address optional for master)
Serial.println("Setting up...");

// datasheet says, wait 10us for hardware reset, so lets wait 1000

// gain setup
write_register(CAP_RED, 0x08);
write_register(CAP_GREEN, 0x08);
write_register(CAP_BLUE, 0x08);


// ask for colour data and offset
write_register(CTRL, 0x01);

void loop()
if (read_register(CTRL))

int red, green, blue;
red = read_colour(DATA_RED_LO);
green = read_colour(DATA_GREEN_LO);
blue = read_colour(DATA_BLUE_LO);

Serial.print("red: ");Serial.println(red);
Serial.print("green: ");Serial.println(green);
Serial.print("blue: ");Serial.println(blue);

Serial.print("red_int: ");Serial.println(red_integration_time);
Serial.print("green_int: ");Serial.println(green_integration_time);
Serial.print("blue_int: ");Serial.println(blue_integration_time);

// have to calibrate against blue, because LED has a blue bias otherwise
// it would look like blue has high gain than it does
float P = 1;
int reference = blue;
red_integration_time += (reference - red)*P;
green_integration_time += (reference - green)*P;
blue_integration_time += (reference - blue)*P;

// set the new integration times

// ask for colour data again
write_register(CTRL, 0x01);



May 08, 2009

Facebook python authentication gateway

Edit: it occurred to me what I have below is the basics of a thin facebook api wrapper. I might make it into one at some point in the future.

If you don't know what this does, you don't need it. Hope this helps some one. Written because pyfacebook is broken, always returns error 100.


def get_session(auth_token):

sorted = params.items()
sorted.sort(key=lambda x:x[0])

str_to_hash = ''.join(["%s=%s"%(x[0], x[1]) for x in sorted])
str_to_hash += FB_API_SECRET

md5 = hashlib.md5()

sig = md5.hexdigest()

params["sig"] = sig

encoded_params = urllib.urlencode(params)
headers = {

conn = httplib.HTTPConnection(FB_API_HOST)
conn.request("POST", FB_API_PATH, encoded_params, headers)

response = conn.getresponse()

print response.status, response.reason

This Works For Me when I use it with iphone facebook-connect client:

[FBSession sessionForApplication:myApiKey getSessionProxy:myURL delegate:self];