Jetson TX1 & OpenCV & Servos

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX1
1

Dear all,

Just about a small investigation from my part.
How the Jetson TX1 could pilot pan & tilt servos through OpenCV.
If you are interested, this work is based on the lib made by Jetsonhacks:

https://www.jetsonhacks.com/2015/10/14/pwm-servo-driver-board-nvidia-jetson-tk1/

This soft permit to a mouse to pilot servos through the video flow of an USB webcam connected to the Jetson TX1.

First, check you have the PCA9685 breakout board:

https://www.adafruit.com/product/815

Second, connect the PCA9685 as follow on the J21 Header connector:

PCA9685 → TX1 (J21 header)

+Vcc → J21: pin 2 (+5V)
GND → J21: pin 3
SDA → J21: pin 27
SCL → J21: pin 28

Third, connect the servo on the PCA9685 breakout board

Servo 1 → Pan → row 0
Servo 2 → Tilt → row 1

Then download the lib from JestonHack as mentioned below.
Download also the lib I2C like this:

sudo apt-get install libi2c-dev

Once it’s done, create on the Jetson TX1 a folder named: testOpeCV
Paste the 2 sources files and the example file of the Jetsonhacks lib.
You will have this :

Directory: testOpenCV
Files within the directory:
JHPWMPCA9685.cpp
JHPWMPCA9685.h
servoExample.cpp

Then modify the servoExample as follow:

#include <iostream>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui.hpp>
#include <JHPWMPCA9685.h>

using namespace std;
using namespace cv;

/* global variables - MouseHandler */
int pan = 90; //row 0 PCA breakout board
int tilt = 90; //row 1 PCA brekout board
Mat frame;

int mapping(int, int, int, int, int);
void moveMouse(int, int, int, int, void*);

int main() 
{
    /* values set for a common servo */
    int servoMin = 140 ;
    int servoMax = 590 ;

    VideoCapture cap(CAP_ANY); // just for USB cam

    PCA9685 *pca9685 = new PCA9685() ;
    pca9685->openPCA9685();

    pca9685->setAllPWM(0,0) ;
    pca9685->reset() ;
    pca9685->setPWMFrequency(60) ;

    while(true)
    {
        cap >> frame;

        setMouseCallback("Frame", moveMouse, NULL);

        /* mapping to follow the screen resolution (640x480) */
        pca9685->setPWM(0,0,map(pan,0,640,servoMin, servoMax));
        pca9685->setPWM(1,0,map(tilt,0,480,servoMin, servoMax));

        imshow("Frame", frame);
        waitKey(30);
    }
    destroyAllWindows();
    pca9685->closePCA9685();
    return 0;
}

int mapping(int x, int in_min, int in_max, int out_min, int out_max) 
{
    int toReturn =  (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min ;
    return toReturn ;
}

void moveMouse(int event, int x, int y, int flags, void* userdata)
{
    if(event == EVENT_MOUSEMOVE)
    {
	pan = x;
	tilt = y;
    }
}

Save the code, and compile like this (Always on the Jetson TX1):

g++ servoExample.cpp JHPWMPCA9685.cpp - o servoExample `pkg-config --cflags --libs opencv` -lopencv_core -lopencv_highgui -lopencv_video -lopencv_videoio -lopencv_imgproc

Don’t forget to plug the power to the breakout board (6Vcc) ;-)
then, launch the soft with the root access:

sudo ./servoExample

Now you can pilot the webcam with the mouse…enjoy !

Christophe

2

Great! Thanks for sharing!!

3

Could anyone please help me in finding a python library for servo motor controlling with PCA9685?