WEBVTT 00:00.260 --> 00:06.290 In this laboratory lesson, we are going to develop a simple python node that listens for messages coming 00:06.290 --> 00:13.100 from the Arduino through the serial port and republish each new message received into our Ros2 topic. 00:13.580 --> 00:18.590 If you are only interested in the plus Cplusplus development, then you can skip to the next lesson 00:18.590 --> 00:23.330 in which we are going to implement the same node with the same functionalities in C plus plus. 00:24.000 --> 00:28.650 So let's go back in Visual Studio code and in the Arduino board firmware package. 00:28.650 --> 00:34.350 And as we are inserting a Python node, let's go to the Arduino board firmware folder. 00:34.560 --> 00:40.200 And here let's create a new file called Simple serial 00:43.380 --> 00:45.450 Receiver Dot Pi. 00:45.630 --> 00:54.690 Let's begin by declaring the directory of the python interpreter And so user bin and the environment 00:54.690 --> 00:56.700 is Python three. 00:57.090 --> 01:02.820 Then since in this script we are going to develop a simple python node that publishes messages within 01:02.820 --> 01:03.870 our Ros two topic. 01:03.900 --> 01:09.430 We can copy the code from the simple publisher which we have already implemented in the Arduino board. 01:09.480 --> 01:10.890 Pi examples. 01:10.890 --> 01:12.780 So the simple publisher. 01:13.170 --> 01:16.800 So let's copy all its content and let's paste it here. 01:17.010 --> 01:20.550 Let's just change the name of the class to be the simple. 01:22.480 --> 01:25.600 Serial receiver. 01:26.380 --> 01:28.630 So let's change it also here. 01:28.630 --> 01:35.410 And let's change the name of the variable that is the simple serial receiver. 01:38.950 --> 01:40.810 And let's change it also here. 01:40.810 --> 01:45.820 And then let's finally change also here, the name of the node that we want to start. 01:46.420 --> 01:51.070 That is the simple serial receiver. 01:51.490 --> 01:56.470 Let's also change the name of the topic in which we want to publish messages that are coming from the 01:56.470 --> 01:57.250 Arduino. 01:57.550 --> 02:03.250 And so let's call this one serial receiver. 02:03.250 --> 02:10.060 And here in this topic, we are still going to publish string messages so we can keep the same interface 02:10.210 --> 02:12.070 from the standard messages. 02:12.750 --> 02:18.540 For the scope of this script, of this note, we are not going to need the counter so we can remove 02:18.540 --> 02:23.610 this variable and also we can remove it from here. 02:24.580 --> 02:28.630 So let's remove the entire message here. 02:28.630 --> 02:32.080 And furthermore, let's also change the variable frequency. 02:32.080 --> 02:36.370 So this one to be 0.01. 02:36.370 --> 02:41.110 So this way the Ros two timer executes the timer callback function. 02:41.110 --> 02:45.430 So this one every 0.01 seconds. 02:45.430 --> 02:48.940 So basically with a frequency of 100Hz. 02:49.860 --> 02:54.990 At this point, we can implement the actual logic to publish any new message that is received from the 02:54.990 --> 02:55.740 serial port. 02:55.740 --> 03:01.530 So from the Arduino into the Ros2 topic that is called serial receiver. 03:02.250 --> 03:06.510 So let's remove also this message here. 03:07.110 --> 03:09.180 And let's start by importing. 03:11.330 --> 03:14.090 The serial library. 03:14.090 --> 03:15.680 So the serial library. 03:15.860 --> 03:20.030 And let's use it to create a new object of the serial class. 03:20.480 --> 03:29.420 So here, let's call this one Arduino And this is an instance of the serial class. 03:29.840 --> 03:34.310 And so from the serial library, let's create an instance of the serial class. 03:34.460 --> 03:40.310 And the constructor of this class requires two inputs the port of our PC to which the Arduino board 03:40.310 --> 03:46.280 is connected via the USB cable and also the baud rate that is used for the communication with the Arduino 03:46.280 --> 03:47.360 through its port. 03:47.840 --> 03:53.840 Instead of hard coding these values, as we also did for the serial transmitter dot pi file, let's 03:53.840 --> 04:00.650 use the Ros two parameters so we can exactly copy the same things that we have done for the simple serial 04:00.650 --> 04:01.490 transmitter. 04:01.880 --> 04:08.810 To declare the parameters port and baud rate and then to read them into two variables that are the port 04:08.810 --> 04:11.190 variable and the baud rate variable. 04:11.370 --> 04:14.490 So let's paste it here. 04:15.360 --> 04:17.490 Let's format it a little bit better. 04:17.940 --> 04:19.260 Okay, now it's fine. 04:19.260 --> 04:26.070 And so now let's use these two parameters so the port and the baud rate to initialize here the serial 04:26.070 --> 04:26.940 communication. 04:27.270 --> 04:37.470 So let's set the port to be the port and the baud rate to be the variable baud rate. 04:38.170 --> 04:43.660 And let's also set the timeout of 0.1. 04:44.810 --> 04:47.140 Now within the timer callback function. 04:47.140 --> 04:52.750 So this one, the one that is executed at regular time intervals by the Ros two timer. 04:52.780 --> 04:59.830 Let's first verify that the Ros two node is still running, so it's still in execution by using the 04:59.990 --> 05:01.330 Rql library. 05:01.450 --> 05:03.450 And let's check the function. 05:03.460 --> 05:05.470 Okay, so let's check that. 05:05.470 --> 05:07.840 Actually, Ros is still in execution. 05:07.840 --> 05:14.140 And also let's check that the serial communication with the Arduino is still open. 05:14.230 --> 05:21.940 So here let's change this variable to Arduino underscore and here let's verify that the communication 05:21.940 --> 05:25.210 is open in this case. 05:25.210 --> 05:31.450 So if both these conditions are met, we can actually start by reading the messages that are coming 05:31.450 --> 05:32.440 from the Arduino. 05:32.560 --> 05:36.820 And so we can use the still Arduino object. 05:36.940 --> 05:41.350 And on this one, let's call the function read line. 05:41.650 --> 05:48.290 So let's use this function to read an entire message, an entire line, and let's store this one into 05:48.290 --> 05:50.840 a new variable called data. 05:52.360 --> 05:56.810 Next, let's try to decode the content of this data variable. 05:56.830 --> 05:58.630 So let's try. 05:59.140 --> 06:08.860 Data decode to decode this one using the UTF eight format and otherwise. 06:08.860 --> 06:10.450 So if we are not able. 06:11.500 --> 06:14.140 Let's simply terminate the execution. 06:14.140 --> 06:16.450 So let's simply terminate this script. 06:16.450 --> 06:17.590 So here it is. 06:17.620 --> 06:18.610 Except. 06:20.530 --> 06:21.220 This one. 06:21.860 --> 06:24.470 Let's adjust the formatting of this script. 06:25.850 --> 06:27.950 So let's remove one tab character. 06:28.490 --> 06:29.900 And also for this one. 06:31.160 --> 06:33.260 So let's verify also. 06:33.260 --> 06:33.980 This one is fine. 06:38.060 --> 06:39.200 Okay now it's fine. 06:40.560 --> 06:43.190 Now here after the try statement. 06:43.190 --> 06:49.190 So if we reached this point, it means that we were able to decode correctly the message that we received 06:49.190 --> 06:50.240 from the Arduino. 06:50.540 --> 06:56.570 Let's publish a new message within the topic that we named Serial receiver. 06:56.570 --> 06:57.620 So this one. 06:57.950 --> 07:00.380 So let's first create a new message. 07:00.380 --> 07:12.620 So this one goes within the if statement, and then let's set the message data to be equal to the content 07:12.650 --> 07:15.830 of the data variable after converting it to a string. 07:15.830 --> 07:17.900 And then let's publish the message. 07:17.900 --> 07:22.010 So with the function publish, let's save this note. 07:22.190 --> 07:29.090 And with this the simple serial receiver class is completed and also our python node is ready to read 07:29.090 --> 07:35.690 messages from the serial port where the Arduino is connected and to republish them to our ros2 topic. 07:36.140 --> 07:41.990 As a final step for this lesson, let's install this node in the cmakelists.txt. 07:42.360 --> 07:49.080 And so in the install section where we installed the simple serial transmitter dot pi, let's add a 07:49.080 --> 07:57.330 new line in which we install the simple serial receiver dot pi. 07:58.140 --> 08:00.120 We don't need to modify for this time. 08:00.120 --> 08:06.150 The package dot XML of the Arduino bot firmware since we haven't added any new dependencies and we are 08:06.150 --> 08:10.140 still using the same ones of the simple serial transmitter. 08:10.320 --> 08:16.920 So now we can directly proceed to rebuild our workspace to see that we don't have made any mistake. 08:17.250 --> 08:22.020 So let's go to the Arduino bot workspace and let's build it. 08:23.740 --> 08:29.440 In the next laboratory lesson after developing the node with the same functionalities in C plus plus, 08:29.440 --> 08:34.750 we are going to start this node and see how it works and see how it establish the communication with 08:34.750 --> 08:38.740 the Arduino and it starts receiving messages from the Arduino board.