WEBVTT 00:00.140 --> 00:06.110 In this laboratory lesson, we will develop a simple C plus plus node that listen for messages coming 00:06.110 --> 00:11.720 from the Arduino through the serial port and republish each new message that is received from the Arduino 00:11.720 --> 00:13.850 into a ros2 topic. 00:14.420 --> 00:20.510 So let's go back to Visual Studio Code and let's start by creating a new script within the Arduino board 00:20.540 --> 00:21.590 firmware package. 00:21.590 --> 00:23.120 So within the source folder. 00:23.240 --> 00:32.120 And here let's call this new script Simple serial Receiver Dot CP. 00:33.690 --> 00:38.930 As you see in this script, we are going to develop a simple C plus plus node that publish some messages 00:38.930 --> 00:40.430 within a ros2 topic. 00:40.460 --> 00:47.420 We can copy the code from the simple publisher that we have already created within the Arduino CP examples. 00:47.570 --> 00:48.950 So this one. 00:48.950 --> 00:53.510 So let's copy its content and let's paste it here. 00:53.600 --> 01:03.050 Let's just change the name of the class to be the simple serial receiver. 01:03.410 --> 01:07.340 And so let's change it also into the name of the constructor. 01:07.610 --> 01:14.150 Then here, when we define that, the timer callback function now belongs to the simple serial receiver 01:14.150 --> 01:14.960 function. 01:15.110 --> 01:16.620 And also here. 01:16.640 --> 01:22.940 So now the implementation of the node is an implementation of the simple serial receiver class. 01:23.060 --> 01:25.190 Let's also change here the name of the node. 01:26.040 --> 01:34.350 To be the simple serial receiver and the name of the topic in which we want to publish the message. 01:34.350 --> 01:40.890 So this one is the serial receiver topic. 01:41.820 --> 01:42.980 Also in this topic. 01:42.990 --> 01:49.110 So the serial receiver, we are going to publish string messages so we can keep the message interface. 01:49.110 --> 01:53.100 This one so unchanged to be the standard message string. 01:53.780 --> 01:56.570 We are not going to need any counter variable. 01:56.570 --> 02:04.430 So actually we can remove everything from here and also we can remove the counter variable here. 02:05.060 --> 02:08.060 And also let's change the counter from here. 02:08.330 --> 02:11.810 And furthermore, let's change the frequency of the timer. 02:11.810 --> 02:16.250 So this one for the moment, this is set to one second. 02:16.280 --> 02:19.940 Let's set it to 0.01 seconds. 02:19.940 --> 02:26.990 And so basically this means that the timer callback function will be executed every 0.01 seconds. 02:26.990 --> 02:31.250 So namely, it will be executed with a frequency of 100Hz. 02:31.580 --> 02:34.970 So let's remove also this message here. 02:35.950 --> 02:42.130 And now we can implement the actual logic in order to send all the messages that we receive from the 02:42.130 --> 02:46.720 serial port, from the Arduino into the serial receiver topic. 02:46.930 --> 02:52.720 To do so, let's start by importing the Lib serial library to interact with the serial port. 02:53.260 --> 03:02.800 So let's include from the Lib serial, the module serial port, and here among the private variable, 03:02.800 --> 03:10.630 let's create a new variable from the lib serial namespace and the serial port class. 03:10.630 --> 03:15.850 And let's call this one Arduino to start the serial communication. 03:15.850 --> 03:21.640 And so to start the communication with the Arduino here in the constructor, we can use the function 03:21.640 --> 03:22.270 open. 03:22.600 --> 03:27.640 So on the Arduino object, let's use the function open. 03:27.640 --> 03:30.970 And this function requires as input the port. 03:30.970 --> 03:36.410 So which is the port of our PC to which the Arduino board is connected through the USB cable. 03:36.710 --> 03:43.070 As this port can change from computer to computer and from user to user, instead of hard coding this 03:43.070 --> 03:46.340 port within this script, let's use some parameters. 03:46.340 --> 03:52.010 So some Ros two parameters as we also did for the simple serial transmitter. 03:52.010 --> 03:58.220 So we can copy exactly these lines here that declares the parameter port. 03:58.220 --> 04:02.440 And then they are reading the value of the parameter port. 04:02.450 --> 04:09.980 So let's paste it also within the simple serial receiver and then let's use this parameter here. 04:09.980 --> 04:14.930 So let's use the port and let's pass it to the open function. 04:15.170 --> 04:23.420 Now, after opening the port, let's also set the baud rate with the function set baud rate for the 04:23.420 --> 04:31.280 communication with the Arduino and from the lib serial from the baud rate. 04:31.310 --> 04:35.570 Let's use the baud rate 115 200. 04:36.140 --> 04:42.620 Now, since in the constructor of the simple serial receiver class, we opened the serial communication 04:42.620 --> 04:43.640 with the Arduino. 04:43.790 --> 04:50.780 So here, when the execution of the node ends, we also need to make sure that the communication with 04:50.780 --> 04:55.580 the serial port is closed so that other nodes and other application can use it. 04:56.030 --> 04:58.830 Therefore, we need to define the destructor. 04:58.850 --> 05:08.240 So the destructor of the simple serial receiver class and within it we need simply to close the connection. 05:08.480 --> 05:12.860 So let's use the serial port and then let's use the function close. 05:13.490 --> 05:18.410 So when the node execution ends, we simply call the close function. 05:18.980 --> 05:24.680 At this point, we can finally implement the logic of this node within the timer callback function. 05:24.680 --> 05:30.950 So the one that is executed at regular time intervals by the Ros two timer and that we want to be executed 05:30.950 --> 05:33.350 with a frequency of 100Hz. 05:33.770 --> 05:36.660 So now in this function, let's first verify that. 05:36.660 --> 05:45.120 Ros So the Ros two node is still executing and so let's use the CP okay, function to verify that Ros 05:45.120 --> 05:46.200 is still executing. 05:46.200 --> 05:52.770 And also let's verify that actually the serial communication with the Arduino is still on by using the 05:52.770 --> 05:53.820 Arduino object. 05:53.820 --> 05:58.200 And then let's check if there is any data available. 05:58.560 --> 06:04.740 And so if in this case there is any new data available, there is any new message available that the 06:04.740 --> 06:06.720 Arduino published on the serial port. 06:06.750 --> 06:07.710 Let's read it. 06:07.710 --> 06:13.050 So let's read those messages with the function read line. 06:13.860 --> 06:20.970 So basically here what we are doing is checking the serial port with a frequency of 100Hz to check if 06:20.970 --> 06:23.400 the Arduino has any new messages for us. 06:23.400 --> 06:25.830 And in this case, we are reading it. 06:26.820 --> 06:30.210 And so let's read its content within this message variable. 06:30.210 --> 06:32.370 So within a new string message. 06:32.520 --> 06:35.730 So let's declare this message above. 06:35.760 --> 06:37.830 So before the if statement. 06:37.830 --> 06:42.960 And then let's read any new messages that the Arduino is publishing within this one. 06:42.960 --> 06:46.410 So within the message data. 06:48.070 --> 06:54.100 And then simply we can publish this message so we can use the publisher to publish the message that 06:54.100 --> 06:58.180 we received from the Arduino within the serial receiver topic. 06:58.930 --> 07:05.500 With this, the simple serial receiver class is completed so we can save our node and now we just miss 07:05.500 --> 07:07.200 to install this script. 07:07.210 --> 07:14.680 So within the cmakelists.txt we need to install it as we installed the simple serial transmitter so 07:14.680 --> 07:21.250 we can just copy the lines that we used for installing the serial transmitter and let's change the name 07:21.250 --> 07:25.150 of the executable to be simple serial receiver. 07:26.050 --> 07:30.880 Then the script, which contains the source code, is the simple cellular receiver. 07:31.060 --> 07:31.480 CPP. 07:31.630 --> 07:35.500 Let's change also here the name of the executable. 07:36.160 --> 07:39.220 And then we need also to list this executable here. 07:39.220 --> 07:45.550 So in the install statement, let's save also this file and we don't need for the moment to modify the 07:45.550 --> 07:52.210 package dot XML within the Arduino board firmware since we haven't added any new dependencies compared 07:52.210 --> 07:56.590 to those that we have already declared and used for the simple serial transmitter. 07:56.590 --> 07:59.110 So all the dependencies are correctly declared. 07:59.230 --> 08:05.350 So now to finish this lesson, let's just build our workspace to check that we have not made any mistake. 08:06.100 --> 08:10.480 So let's go to the Arduino board workspace and let's build it. 08:13.870 --> 08:15.810 And so the build is successful. 08:15.820 --> 08:21.010 And so in the next laboratory lesson, we will start this node and we will see how it works. 08:21.010 --> 08:26.560 And so how it receives messages from the Arduino through the serial port and how it republish those 08:26.560 --> 08:29.080 messages into our ros2 topic.