WEBVTT 00:00.230 --> 00:06.130 In this laboratory lesson, we are going to develop a simple python node that subscribes to our ros2 00:06.140 --> 00:11.930 topic and republish every new message it receives on the Arduino serial port. 00:12.320 --> 00:17.330 If you are interested only in the Cplusplus development, then as always, you can skip to the next 00:17.330 --> 00:22.820 lesson in which we are going to implement the same node with the same functionalities in C plus plus. 00:24.540 --> 00:29.400 Making Visual Studio code in the newly created Arduino board firmware package. 00:29.430 --> 00:34.190 Let's create a new folder that is called as the Package itself. 00:34.200 --> 00:38.520 So Arduino boot firmware. 00:39.480 --> 00:47.760 And in order to create a new Python node, let's add a new file within this folder called init dot pi 00:47.760 --> 00:49.050 that we leave empty. 00:49.260 --> 00:54.030 And then let's also add one more file that will actually contain the logic of our node. 00:54.030 --> 01:02.880 And let's call this one simple serial transmitter dot pi. 01:03.330 --> 01:07.410 Here, let's start by declaring the python interpreter directory. 01:07.800 --> 01:17.250 So this is in the user bin and the environment is the Python three that we are going to use. 01:17.490 --> 01:23.430 And then since in this script we are going to develop a simple python node that subscribes to our ros2 01:23.460 --> 01:24.160 topic. 01:24.160 --> 01:31.690 We can copy the content of the simple subscriber python node that we created in the Arduino Pi examples. 01:31.870 --> 01:34.690 So the simple subscriber here. 01:34.870 --> 01:38.710 So let's copy all its contents and let's paste it here. 01:38.710 --> 01:41.830 So we have already a node that implements a subscriber. 01:42.130 --> 01:44.290 Let's just change the name of the class. 01:44.290 --> 01:51.970 So this one to be simple serial transmitter. 01:52.060 --> 01:55.330 And also we need to change it within the main function. 01:55.330 --> 02:03.940 So here let's also change the name of the variable to simple serial transmitter. 02:04.180 --> 02:11.980 So the Pi will spin this node and when we press control C, we are going to destroy this simple serial 02:11.980 --> 02:13.120 transmitter node. 02:13.360 --> 02:15.550 Next, let's also change the name of the node. 02:15.550 --> 02:23.260 So this one, let's call it simple serial transmitter. 02:23.260 --> 02:25.030 And this is subscribed. 02:25.030 --> 02:34.150 So the subscription is to the topic serial transmitter, in which we are still assuming that string 02:34.150 --> 02:35.560 messages are published. 02:35.560 --> 02:40.420 And so we can leave the type of the message of the interface as a string. 02:40.450 --> 02:46.840 Now within the message callback function, which is executed when we receive a new string message within 02:46.840 --> 02:52.750 the serial transmitter topic, we can implement the actual logic that sends each new message that was 02:52.750 --> 02:57.010 received within this topic to the serial port and so to the Arduino. 02:57.490 --> 02:58.240 To do so. 02:58.240 --> 03:03.670 In Python, there is a library that we have already installed in one of the first lessons of this course 03:03.670 --> 03:05.560 that is called Pyserial. 03:05.860 --> 03:13.390 So let's start by importing this serial library and now let's use it to create a new object of this 03:13.390 --> 03:13.720 class. 03:13.720 --> 03:15.550 So of the serial class. 03:16.420 --> 03:24.700 And so from the cereal library, let's create a new instance of the cereal class and let's save it to 03:24.700 --> 03:25.720 a new variable. 03:27.280 --> 03:30.070 That is called Arduino. 03:30.070 --> 03:33.640 And so this is an implementation of the serial class. 03:33.730 --> 03:37.280 And the constructor of this class requires two inputs. 03:37.300 --> 03:43.660 The first one is the port of our PC, to which the Arduino board is connected through the USB cable. 03:43.660 --> 03:49.180 And also the second parameter is the baud rate that we need to use for the communication with the Arduino 03:49.180 --> 03:50.470 through the serial port. 03:51.030 --> 03:54.030 Instead of hard coding these values into the script. 03:54.060 --> 03:58.860 As for example, different users may connect the Arduino to a different port or their PC. 03:59.340 --> 04:04.340 We are going to use the two parameters to configure these serial class. 04:04.380 --> 04:07.320 So let's start by declaring two parameters. 04:07.470 --> 04:14.550 So here, after the initialization of the base class, let's declare two parameters with the function 04:15.720 --> 04:21.510 declare parameter, and the first one is the port. 04:21.750 --> 04:30.420 And by default, I set this one to the port dev ty and in my case is the ACM zero port. 04:30.420 --> 04:40.710 And then the second parameter still with the declared parameter is the boot rate that by default I set 04:40.710 --> 04:43.980 to 115 200. 04:44.620 --> 04:50.770 So, you know the startup, whenever we execute the constructor of the simple serial transmitter class, 04:50.800 --> 04:53.110 these two parameters will be declared. 04:53.110 --> 04:58.510 And then also we are going to read the values that are assigned to these parameters, and we can do 04:58.510 --> 05:01.270 so with the get parameter function. 05:01.900 --> 05:11.560 So still from the node class, let's use the get parameter function that we have inherited from the 05:11.560 --> 05:16.990 node class and let's read the content of the port value. 05:17.170 --> 05:25.450 So let's read this content and let's store this one into a new variable called, for example, port. 05:25.810 --> 05:27.280 Let's do the same. 05:27.940 --> 05:31.060 Also for the second parameter that we have declared for this node. 05:31.330 --> 05:32.440 So the. 05:34.500 --> 05:41.160 Boundary parameter and let's read the content of the boundary parameter. 05:41.790 --> 05:48.780 Now we can use these two variables so the port and the baud rate to initialize the serial communication. 05:48.780 --> 05:52.020 So to initialize this serial object. 05:52.020 --> 06:01.320 And so we need to provide a port that is in the variable port and also we need to provide a baud rate 06:01.650 --> 06:04.770 that is in the variable baud rate. 06:04.890 --> 06:11.220 Finally, let's also set a timeout for this communication to be equal to zero 0.1. 06:12.110 --> 06:18.200 At this point in the message callback function, which is executed upon receiving a new message in the 06:18.200 --> 06:24.980 serial transmitter topic, we can send the received message to the Arduino using the serial object. 06:24.980 --> 06:27.470 So this one that we have just created. 06:27.590 --> 06:33.980 So let's first change here the message that we are going to print in the terminal and let's print the 06:33.980 --> 06:34.800 message. 06:34.820 --> 06:38.690 New message received. 06:39.760 --> 06:47.650 And then publishing on Serial and then followed by the port. 06:47.800 --> 06:52.720 So let's take the port from the serial object. 06:53.290 --> 06:54.830 And let's take the name. 06:54.850 --> 07:02.680 Now, in order to send this message through the serial port, let's use the Arduino object and let's 07:02.680 --> 07:05.260 use the write function. 07:05.260 --> 07:11.490 And so we can write the content of the ros2 message that we have just received. 07:11.500 --> 07:19.600 And let's ensure that it is encoded properly following the UTF eight encoding. 07:20.500 --> 07:25.870 With this, our node is completed, so now we can move on to installing and launching it. 07:25.900 --> 07:27.190 To see how it works. 07:27.640 --> 07:30.850 So in the file cmake list dot txt. 07:31.510 --> 07:37.720 Let's remove all the commented rows to have a better visualization of this file. 07:38.500 --> 07:47.560 And now let's add a new dependency from the amend cmake python in order to compile our python node. 07:47.570 --> 07:54.420 And then let's also add another one from the PY library which we used in our node. 07:54.440 --> 08:09.890 Then let's also use the instruction almond python install package to install the python script within 08:09.890 --> 08:10.940 the current package. 08:10.940 --> 08:13.580 So within the Arduino board firmware package. 08:13.610 --> 08:19.400 Then let's also use an install instruction to install our python node. 08:19.400 --> 08:21.110 And so to install a new program. 08:22.400 --> 08:28.310 And this program that we want to install is within the Arduino board firmware folder. 08:28.490 --> 08:31.160 So the folder that has the same name of the package. 08:31.460 --> 08:38.450 So we refer to this one with the variable project name and then the script that contains the source 08:38.450 --> 08:47.500 code is the simple serial transmitter dot pi and the destination. 08:47.500 --> 08:55.600 So we want to install this one within the lib folder and within the sub folder that has the same name 08:55.600 --> 08:56.680 as the package. 08:56.950 --> 09:01.930 And so again, let's use the project name variable. 09:02.780 --> 09:03.350 Next. 09:03.350 --> 09:07.220 We also need to modify the package dot XML. 09:07.340 --> 09:16.070 And so here we need to add a new build tool dependency from the CMake Python in order to compile our 09:16.080 --> 09:16.610 node. 09:16.700 --> 09:18.860 And then also we need a dependency 09:22.250 --> 09:33.200 from the SQL Pi and also we need an execution dependency from the Python three 09:35.900 --> 09:40.310 serial library that we have used for the communication with the Arduino. 09:40.340 --> 09:41.090 That's it. 09:41.120 --> 09:46.220 Now everything is done and so we can build our workspace and see how it works. 09:46.790 --> 09:48.980 So let's open a new terminal. 09:50.270 --> 09:55.280 Let's go to the workspace and let's build it. 09:55.830 --> 10:01.260 In the next laboratory lesson after developing the node with the same functionalities in Cplusplus, 10:01.260 --> 10:06.540 we are going to start this node and so we are going to see how it works and how it communicates with 10:06.540 --> 10:07.650 the Arduino board.