WEBVTT 00:00.140 --> 00:06.410 In this laboratory lesson, we are going to develop a simple cplusplus node that subscribes to our ros2 00:06.440 --> 00:11.990 topic and republishes every new message it receives on the Arduino serial port. 00:12.590 --> 00:18.110 So back in Visual Studio code, in the Arduino board firmware package that we have just created. 00:18.140 --> 00:20.190 Let's insert the new node. 00:20.210 --> 00:23.200 As always within the source folder. 00:23.210 --> 00:32.630 So here let's create a new file called Simple Serial Transmitter dot CP. 00:33.580 --> 00:39.850 Since we are going to develop a simple C plus plus node that subscribes to our ros2 topic, we can copy 00:39.850 --> 00:46.660 the code from the simple subscriber node that we have already created within the Arduino bot CP examples 00:46.900 --> 00:50.530 and we called simple subscriber dot CP. 00:50.800 --> 00:55.480 So let's copy its content and let's paste it here. 00:56.000 --> 00:56.510 Here. 00:56.510 --> 00:58.550 We just need to change the name of the class. 00:58.940 --> 01:04.640 So let's call it simple serial transmitter. 01:04.760 --> 01:06.830 And also, we need to change it. 01:07.930 --> 01:09.790 In the name of the constructor. 01:10.450 --> 01:16.600 And also here when we create the node and finally here, when we declare the message callback function 01:16.600 --> 01:20.320 that now belongs to the simple serial transmitter class. 01:20.620 --> 01:22.400 Let's also change the name of the node. 01:22.420 --> 01:31.690 So here this is the simple serial transmitter and let's change the name of the subscriber. 01:31.810 --> 01:36.310 So this one now is subscribed to the topic serial 01:38.830 --> 01:39.850 transmitter. 01:40.420 --> 01:47.590 Still in this topic, we are going to publish string messages so we can leave the type of the message. 01:47.590 --> 01:51.970 So the interface that is used for the communication within this topic unchanged. 01:51.970 --> 01:58.690 So we can leave this one to be string messages and now we can implement the actual logic that sends 01:58.720 --> 02:05.350 each of the messages received on the serial transmitter topic to the Arduino through the serial port. 02:06.050 --> 02:12.380 For this, we can use the lib serial library that is available in C plus plus and that we have downloaded 02:12.380 --> 02:15.110 in the first setup lessons of this course. 02:15.290 --> 02:17.840 So let's start by including this library. 02:18.080 --> 02:22.730 So let's include the lib serial library. 02:22.730 --> 02:26.720 And from this one, let's take the definition of the serial port. 02:27.280 --> 02:33.880 Then here, among the private variables of the simple serial transmitter class, let's add a new private 02:33.880 --> 02:34.600 member. 02:34.600 --> 02:41.080 So from the lib serial, let's create a new object of type serial port. 02:41.080 --> 02:44.410 And let's call this one Arduino. 02:45.850 --> 02:48.730 Now to start the communication with the serial port. 02:48.760 --> 02:56.200 We can use the open function so we can take this object and here within the constructor we can call 02:56.200 --> 03:00.190 the function open on the serial object. 03:00.640 --> 03:06.820 And this function requires as input the port of our PC to which the Arduino board is connected through 03:06.820 --> 03:13.180 the USB cable instead of hard coding these values in the script, as of course it might change from 03:13.180 --> 03:15.400 user to user and from PC to PC. 03:15.820 --> 03:20.530 We can use the ros2 parameters to dynamically configure these values. 03:20.620 --> 03:27.580 So here, let's start by declaring a new parameter for this node with the declare parameter function 03:27.580 --> 03:30.430 which we are inheriting from the node class. 03:30.640 --> 03:33.310 And this first one is a string. 03:34.360 --> 03:43.120 So we want the type of this parameter to be a string and let's name it port and by default, in my case, 03:43.120 --> 03:49.040 I'm going to set it to the port dev 80 ACM zero. 03:49.040 --> 03:51.710 So to the port ACM zero of my PC. 03:52.880 --> 03:54.200 It did not start up. 03:54.200 --> 03:58.700 So when actually the node starts, we want to read this parameter. 03:58.700 --> 04:04.310 So with this instruction we are declaring this parameter and now we want also to read it in order to 04:04.310 --> 04:12.710 use it to open the communication with the correct port so we can use the function get parameter which 04:12.710 --> 04:15.470 still we are inheriting from the node class. 04:15.650 --> 04:24.290 And let's read the content of the parameter port and let's save it as a string. 04:24.320 --> 04:29.600 Since we have declared this to be a string and let's store it within a new variable. 04:30.950 --> 04:34.430 So within a new string variable that we call port. 04:34.580 --> 04:38.810 And so it contains the output of this get parameter function. 04:39.650 --> 04:45.860 Now we can use this variable here so the port and we can pass it to the open function so that it will 04:45.860 --> 04:49.460 start opening the serial communication with the requested port. 04:49.460 --> 04:51.110 So with the defined port. 04:52.010 --> 04:58.370 After opening and initializing the communication, we also need to define the baud rate at which the 04:58.370 --> 04:59.930 communication should occur. 05:00.380 --> 05:06.230 So again, on the Arduino object, let's use the function set baud rate. 05:06.500 --> 05:08.100 And let's set this one. 05:08.120 --> 05:14.330 So from the lib serial, let's set the baud rate to be this one. 05:14.330 --> 05:17.990 So 1115 200. 05:18.230 --> 05:24.140 Since we opened the serial communication with the Arduino in the constructor of the simple serial transmitter 05:24.140 --> 05:28.640 class, we also need to close it when the nodes ends its execution. 05:28.640 --> 05:31.100 And so this way we need to prevent that. 05:31.100 --> 05:33.350 The connection remains open forever. 05:33.980 --> 05:41.960 To do so, we can create the destructor so the simple serial transmitter destructor. 05:41.960 --> 05:47.060 And within this function, let's simply close the connection. 05:47.060 --> 05:53.760 So if it was open, so if the connection was still open with the Arduino, so with the serial port, 05:53.790 --> 06:00.120 this destructor that is called when we Destroy the node will automatically close the connection so that 06:00.120 --> 06:04.050 other nodes and other application can use the serial communication. 06:04.940 --> 06:07.970 Now at this point in the message callback function. 06:07.970 --> 06:14.810 So here, which is executed upon receiving a new message in the serial transmitter topic, we just want 06:14.810 --> 06:20.060 to send the message that was just received to the Arduino using the serial port. 06:20.330 --> 06:24.590 So let's first change the message that we are going to print in the terminal. 06:24.590 --> 06:38.690 So the informative message here and let's print new message received and then publishing on serial port 06:38.870 --> 06:42.530 and followed by the message data. 06:42.860 --> 06:48.020 So this one is the message that we are going to publish to the serial port. 06:48.470 --> 06:55.910 Now in order to publish this message to the serial port, so in order to write this message to the Arduino, 06:56.390 --> 06:59.870 let's use the function, right? 07:00.590 --> 07:06.390 And so this function takes as input the message that we want to publish so that we want to transmit 07:06.390 --> 07:07.680 through the serial port. 07:07.860 --> 07:13.050 And this is the content of the message that we just received within the topic. 07:13.050 --> 07:14.780 So message data. 07:15.470 --> 07:20.690 Let's just remove the cost statement of this function. 07:20.690 --> 07:27.500 And so now is fine because otherwise it won't be able to modify any object of the class. 07:27.830 --> 07:33.710 With this, our node is completed and so now we can move on to install and launching it to see how it 07:33.710 --> 07:34.330 works. 07:34.340 --> 07:39.170 So let's start by installing it within the file Cmakelists.txt. 07:39.890 --> 07:51.530 And here let's add the dependency from the Rql CPP library and also another one from the standard messages. 07:54.950 --> 07:58.430 From which we have used the definition of the string message. 07:58.730 --> 08:02.660 Then also we need to declare the dependency from the serial library. 08:03.320 --> 08:07.070 So let's use the package. 08:09.000 --> 08:21.990 Config and let's use this one for the instruction package, check modules and check the serial module 08:22.770 --> 08:26.340 and so the lib serial library. 08:26.550 --> 08:32.910 Now to compile and make our node executable, let's add a new instruction. 08:33.180 --> 08:36.830 Add executable. 08:36.840 --> 08:48.390 Let's call our executable simple serial transmitter and the source code is in the source folder and 08:48.390 --> 08:54.570 is in the simple serial transmitter dot cpp. 08:55.460 --> 09:02.780 Then also let's specify the dependencies that this node needs with the aim and target 09:05.000 --> 09:06.090 dependencies. 09:06.140 --> 09:09.950 So the node is the simple serial transmitter. 09:11.360 --> 09:19.490 And it needs the dependency from the CPP library, from the standard messages, and also in order to 09:19.490 --> 09:29.030 add the dependency from the Lib serial library, let's use another instruction of type target include. 09:31.340 --> 09:32.890 A directories. 09:33.070 --> 09:36.760 So still for the simple serial transmitter node. 09:37.000 --> 09:39.760 Let's declare the usage of the library. 09:40.450 --> 09:49.550 So let's declare the serial include dears. 09:50.230 --> 09:51.610 Here is dears. 09:51.970 --> 09:59.460 Finally, we need one more instruction that is target link libraries. 09:59.470 --> 10:07.690 Still, for the simple serial transmitter node, this is public, and for the simple serial transmitter 10:07.690 --> 10:12.880 node, we need to add the serial. 10:14.560 --> 10:17.340 And this goes into the double quotes. 10:17.350 --> 10:22.870 So this one and also this variable here goes into the double quotes. 10:23.500 --> 10:28.450 Now to install the executable, let's add a new install instruction. 10:30.070 --> 10:40.930 So here and let's install the target that we want to install is the simple serial transmitter node. 10:41.440 --> 10:49.660 So this one and the archive destination is the lib folder. 10:49.930 --> 10:52.420 Then the library 10:55.360 --> 11:06.160 destination is again the lib folder and the runtime destination is the bin folder. 11:06.580 --> 11:15.250 And the destination of the executable is the lib folder and the sub folder that has the same name of 11:15.250 --> 11:16.150 the package. 11:16.270 --> 11:21.400 And so we access with the project name variable. 11:22.300 --> 11:24.980 Also let's modify the package dot XML. 11:25.000 --> 11:32.860 Since we added some more dependencies to this email list and here let's add the dependency from the 11:34.600 --> 11:36.730 RCL cpp library. 11:37.090 --> 11:45.100 Then another one from the standard messages library and then another one. 11:45.930 --> 11:51.480 From the lib serial dev library. 11:52.260 --> 11:54.750 With this change, everything is set. 11:54.780 --> 12:00.390 So now we can conclude this lesson by building our workspace in order to see that everything compiles 12:00.390 --> 12:02.220 and so that we have no errors. 12:02.610 --> 12:06.210 So let's go to the workspace and let's build it. 12:08.920 --> 12:16.560 We can see indeed that there is an error in our list as this is runtime space destination. 12:16.570 --> 12:21.280 So let's save and let's build the workspace again. 12:21.460 --> 12:24.460 There is also another similar issue. 12:25.180 --> 12:27.130 So with the archive destination. 12:27.130 --> 12:27.940 Correct. 12:28.060 --> 12:32.350 So let's use this space and let's give it one more try. 12:36.140 --> 12:37.940 Now everything compiles. 12:37.940 --> 12:43.130 And in the next laboratory lesson, we are going to start this node and see how it works and so how 12:43.130 --> 12:45.020 it communicates with the Arduino.