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Rich LeGrand, 02/19/2014 06:45 pm


Hooking up Pixy to a Microcontroller like an Arduino

Pixy is meant to talk to a microcontroller, and Pixy comes out of the box ready to talk to an Arduino. Use the supplied Arduino cable to connect Pixy to your Arduino.

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Download the Arduino library "Pixy.zip" here. Bring up the Arduino IDE and import the Pixy library by selecting Sketch➜Import Library... in the Arduino IDE, and then browsing to the Pixy.zip file that you just downloaded.

Next, load the "hello_world" example by selecting it in File➜Examples➜Pixy. Upload it and bring up the Serial Monitor. You should see messages printed that look similar to this:

Detected 1:
  block 0: sig: 1 x: 159 y: 109 width: 61 height: 61
Detected 1:
  block 0: sig: 1 x: 173 y: 114 width: 60 height: 61
Detected 1:
  block 0: sig: 1 x: 146 y: 111 width: 70 height: 65
... 

Note, the example will only print messages if Pixy is running the "default program" and an object that matches one of its color signatures is visible.

Arduino API

Using Pixy with Arduino is really simple. You simply include the SPI and Pixy headers:

#include <SPI.h>  
#include <Pixy.h>

And instantiate a global instance:

Pixy pixy;

The API consists of one call: getblocks(), which returns the number of objects Pixy has detected. You can then look in the pixy.blocks[] array for information about each detected object (one array member for each detected object.) Each array member (i) contains the following fields:

  • pixy.blocks[i].signature The signature number of the detected object (1-7)
  • pixy.blocks[i].x The x location of the center of the detected object (0 to 319)
  • pixy.blocks[i].y The y location of the center of the detected object (0 to 199)
  • pixy.blocks[i].width The width of the detected object (1 to 320)
  • pixy.blocks[i].height The height of the detected object (1 to 200)
  • pixy.blocks[i].print() A member function that prints the detected object information to the serial port

So it's simple to talk to Pixy with your Arduino! Pixy sends block information to Arduino at 1 Mbits/second which means Pixy can send more than 6000 detected objects per second or 135 detected objects per frame.

Other Microcontrollers or Devices

Pixy will output objects that it detects through one of several interfaces that you choose. It supports SPI, I2C, UART, and analog/digital I/O through its 10-pin I/O connector. Pixy also supports USB 2.0 through its mini-USB connector. You can configure which interface Pixy uses through the configure dialog in PixyMon. The "Data out port" parameter determines the output port.

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If you hover the mouse pointer over the "Data out port" text, a help string will be displayed that describes which value corresponds to which type of port.

  • SPI - this is the default port that uses 3 wires (pins 1, 3, and 4 of the I/O connector) and is used to communicate with Arduino
  • I2C - this is a multi-drop 2-wire port (pins 5 and 9 of the I/O connector) that allows a single master to communicate with up to 127 slaves (up to 127 Pixys).
  • analog/digital x - this will output the x value of the largest detected object as an analog value between 0 and 3.3V (pin 3). It also outputs whether an object is detected or not as a digital signal (pin 1 of the I/O connector).
  • analog/digital y - this will output the y value of the largest detected object as an analog value between 0 and 3.3V (pin 3). It also outputs whether an object is detected or not as a digital signal (pin 1 of the I/O connector).

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