Synchronising 2 AR0134 with Usb3.0 Camera Schield


I’m using two AR0134 with USB3.0 Camera schields and trying to get them synchronised, as I need a series of synchronised frames to determine the posiotion and mean speed of a moving object. Well, using the external trigger mode for camera and continuous mode for usb3.0 camera shield I could get some almost synchronised frames, with a phase difference of 0.02 to 0.05 second. I had to use auto trigger. With a pulsed trigger, the phase differences are way to big, around 1 to 1.5 second.

Is it possible to get the phase difference around zero seconds (i.e synchronised frames)? Any suggestion to solve this problem?

Kind regards


Don’t worry and we will try my best to help you.

Q1: using the external trigger mode for camera and continuous mode for usb3.0 camera shield I could get some almost synchronized frames, with a phase difference of 0.02 to 0.05 second

A1: We want to know How do you estimate this time? What is the basis of the assessment? We think in external mode, the phases should be absolutely in sync. We need to know your hardware connection and the command you are running.

Q2: About auto-trigger you have mentioned, I don’t understand the difference between the external trigger mode. Please tell us the detail information.


Hello there,

thank you for your quick response.

External trigger: usually an external trigger could be a signal that puts the trigger pin in camera module high. So i used an square wave which has a period of 25 millisecond (frequency 40 Hz), whereas it is high for 1 millisecond and low for the rest of time (24 millisecond).

Auto trigger : in auto trigger, it’s not a squre wave but a constant signal. Lets say, it puts the camera trigger pin high at time, t = 0 and stays high for the rest of the time .

I’m using an arduino uno board to produce the above described signal. Trigger pins and Gnd pins of both cameras are parallel connected with an arduino uno. To find out if the frames are synchronised, I use a digital stop watch app from smartphone and save the frames with a time stamp. Every time stamp has 4 consequent frames for each camera.

Description of Code:

Three threads are initialised, two threads for CaptureImage, each one with its own Handle (ArduCamHandle) and one thread for readImage with two Handles. In readImage function a little modification has been done. The “while” loop looks like this:


beginTime = clock(); //time stamp

vector<cv::Mat> Bilder1, Bilder2;


if (ArduCam_avaiableImage(handle) > 0 && ArduCam_availableImage(handle2) > 0) {

rtn_val = Arducam_readImage(handle, frameData);
rtn_val2 = Arducam_readImage(handle2, frameData2);

if (rn_val == USB_CAMERA_NO_ERROR && rn_val2 == USB_CAMERA_NO_ERROR) {

int begin_disp = clock();

rawImage = ConvertImage(frameData); rawImage2 = ConvertImage(frameData2);

if (! || !{

std::cout << “No image data \n”;

Bilder1.push_back(rawImage.clone()); // To append the frames in the vector


if (Bilder1.size()==5){

if (save_flag){

for (int i = 1; i< Bilder1.size(); i++){

… // some other codes for image processing…

//Image name with a time stamp

sprintf(imageName,“Cam1/%ld_%d.jpg”, beginTime, i);

sprintf(imageName2,“Cam2/%ld_%d.jpg”, beginTime, i);

cv::imwrite(imageName, Bilder1[i]);

cv::imwrite(imageName2, Bilder2[i]); }


// To empty the Vectors

vector<cv::Mat>().swap(Bilder1); vector<cv::Mat>().swap(Bilder2); beginTime = clock(); //New time stamp for next image series


ArduCam_del(handle); ArduCam_del(handle2);





The external trigger connection with the camera module can be seen in the following picture.

connection to trigger and gnd in CameraModule



Kind regards

Hello Bin,

I woluld like to thank you for your quick response.

My last post (March 5, 2020) is still awaiting moderation.

Auto trigger is still an external trigger; the differecne is the trigger pin stays always high in auto trigger mode, whereas in pulsed trigger it is an squre wave signal, lets say, it stays for 1 millisecond high and for 24 millisecond low, so that it has a period of 25 millisecond (i.e frequency of 40 hz).

Hardware setting: The trigger and gnd pins of both camera modules has been connected parallel with an arduino uno digital pin (pin 13) and digital gnd pin. Arduino uno produces an output of constant 5 V in auto trigger mode and in pulsed trigger mode a squaure wave signal with a peak of 5 V in 40 Hz frequency as above described.

Code description: Two threads of captureImage with different handles (for 2 cameras) are initialised. The frames from both cameras are appended in two different vectors in readImage thread. Once the size of these vector is 5 and the save_flag (boolean) is true the program saves those frames in JPEG format in instructed path with a time stamp (naming convention: timeStamp_frameNumber) and empties the vectors afterwards (if save_flag is false, it skips the saving part).

Assesment of phase difference: To determine, if the cameras are synchronised or not, a digital stop watch with an accuracy of 0.01 second was hold in front of those cameras and the frames have been saved with time stamp which could be assesed later on.


However, the frames are almost synchronised, from 5 frames with an identical time stamp perhaps 2 or 3 (the number differs in different time stamp) are synchronised and the rests are not. Besides, the frame rates are not constant. The time differences between frame to frame are not always same. And this is in the event of auto trigger mode.

In case of pulsed trigger, the frames are not synchronised at all.


Hopefully, this description helps you to find out the problem.

Thank you again,

Warm regards

The problem has been solved. It had a problem connecting the trigger pin.

Kind regards

Great to hear you have solved your problems.