WEBVTT 00:00.080 --> 00:01.820 In this new activity. 00:01.820 --> 00:08.180 And just before we go to check the Raspberry Pi functionalities, we are going to use the servo motor 00:08.180 --> 00:09.800 and also the push button. 00:09.800 --> 00:16.310 So basically, the Raspberry Pi here will be responsible to do a sweep of the servo. 00:16.310 --> 00:18.140 So you can check one of the previous lesson. 00:18.140 --> 00:21.020 When did the code for the servo motor? 00:21.050 --> 00:28.730 And basically the sweep is that you're going to go from the angle zero to angle 180 on the servo motor 00:28.730 --> 00:34.370 and then come back from 182 zero with a small delay in between. 00:34.370 --> 00:34.550 Okay. 00:34.580 --> 00:36.680 For example, ten milliseconds. 00:36.680 --> 00:38.510 That was our example. 00:38.510 --> 00:43.910 And so you will see the servo going from the minimum position to the maximum coming back to the minimum. 00:43.910 --> 00:44.540 ET cetera. 00:44.570 --> 00:46.580 ET cetera, in an infinite loop. 00:46.790 --> 00:50.630 But this time we are not going to do the sweep on the Arduino. 00:50.660 --> 00:54.080 We are going to do the sweep on the Raspberry Pi with Python code. 00:54.200 --> 00:54.590 Okay. 00:54.590 --> 00:58.370 So on the Arduino side, the code is going to be actually quite simple. 00:58.430 --> 00:58.760 Okay. 00:58.760 --> 01:05.200 So you're going to read from Serial and receive a servo command, which contains an angle between 0 01:05.200 --> 01:06.390 and 180. 01:06.420 --> 01:13.110 So for this, I don't give you the protocol, but you can get some inspiration from what we did with 01:13.110 --> 01:16.860 the RGB led to send a servo command and a number. 01:16.890 --> 01:17.130 Okay. 01:17.130 --> 01:19.500 So you can do something similar for the servo. 01:19.530 --> 01:23.640 You're also going to read from the push button like we did before. 01:23.640 --> 01:27.750 And when it's pressed, you send a message to the Raspberry Pi and on the Raspberry Pi. 01:27.780 --> 01:30.720 So that is where actually we will have the most code here. 01:30.720 --> 01:35.670 So I have given you some few code examples to help you get started. 01:35.670 --> 01:37.200 So you're going to do a sweep here. 01:37.200 --> 01:39.540 We have, for example, five milliseconds. 01:39.540 --> 01:39.780 Okay. 01:39.780 --> 01:41.610 So here we use seconds. 01:41.610 --> 01:41.820 Okay. 01:41.820 --> 01:50.430 So five milliseconds is 0.005 second in your kind of void loop here in the while true, what you're 01:50.430 --> 01:56.670 going to do is so I have first a timeslip with 0.001. 01:56.670 --> 02:00.090 So again we don't want to make the while true. 02:00.120 --> 02:01.800 Go at full speed. 02:01.800 --> 02:06.990 We want to reduce the speed a bit, which is going to reduce a lot the CPU usage. 02:07.290 --> 02:15.240 And so here before we use 0.01, which is going to make the while loop go at 100Hz here, I'm going 02:15.240 --> 02:18.480 to use 0.001. 02:18.480 --> 02:22.080 So the loop is going to run at 1000Hz, okay? 02:22.080 --> 02:24.150 Because we're going to use that kind of time. 02:24.150 --> 02:24.600 Okay. 02:24.600 --> 02:26.010 Five millisecond. 02:26.010 --> 02:30.390 So we need a loop that runs faster than the delay, actually. 02:30.390 --> 02:30.900 Okay. 02:31.080 --> 02:38.610 And why do this here is because well, we are not going to use time to wait between two changes in the 02:38.610 --> 02:38.970 angle. 02:39.000 --> 02:39.600 Okay. 02:39.630 --> 02:40.380 Why is that? 02:40.380 --> 02:44.280 Because we will also need to read from the sale. 02:44.280 --> 02:48.240 So we don't want to use time slip to block the program. 02:48.240 --> 02:55.170 And so the only time that slip is going to be the one that reduces a bit the speed of the loop here. 02:55.230 --> 02:57.030 And basically we are going to do the same. 02:57.030 --> 02:58.170 As for the Arduino. 02:58.170 --> 03:05.480 So in the Arduino, when we wanted to do an action every X amount of time without using the delay, 03:05.510 --> 03:10.790 we use a structure where we compare the previous time with the current time, and that's what we do 03:10.790 --> 03:11.570 here also. 03:11.570 --> 03:17.330 So what you can do is import the time module and then with time, dot time, you get the current time 03:17.330 --> 03:18.650 in seconds, okay? 03:18.650 --> 03:25.370 And so you can initiate a last time action down to the current time and put an action delay in second 03:25.880 --> 03:27.710 and then in the loop. 03:27.710 --> 03:35.060 Every time simply you get the time and you do the current time minus the last time, the previous time, 03:35.060 --> 03:37.250 which gives you a duration. 03:37.250 --> 03:43.310 And if this duration is greater than the delay, then you do your action and you of course update the 03:43.310 --> 03:46.400 time when the action was done to the current time. 03:46.640 --> 03:46.970 Okay. 03:46.970 --> 03:52.280 And after that, if our before that, if you can also check if you have received something from Serial 03:52.640 --> 03:58.130 and then well, to make the servo sweep, what you can do is you can add a variable that is going to 03:58.130 --> 04:00.440 be, for example, let's say. 04:01.210 --> 04:06.840 Servo going up, like, for example, a Boolean. 04:06.850 --> 04:07.090 Okay. 04:07.090 --> 04:14.110 So if it's going up every time you're going to add plus one to the angle and send plus one from the 04:14.110 --> 04:21.790 current angle until you reach 180 and then you put that to false. 04:21.790 --> 04:23.980 And if you have false, you're going to go down. 04:23.980 --> 04:26.620 So from 180 to 0. 04:26.620 --> 04:31.750 And when you reach zero, you put that to true so you can go up again. 04:31.750 --> 04:33.520 Okay, so that's how you do the sweep. 04:33.520 --> 04:39.460 And I have added another functionality that actually when you press the push button on the Arduino, 04:39.490 --> 04:41.740 you're going to send the message to the Raspberry Pi. 04:41.740 --> 04:45.970 Here, you receive the message and you're going to change the speed. 04:45.970 --> 04:49.210 So the speed is basically the delay. 04:49.570 --> 04:53.080 So the shorter the delay, of course, the higher the speed. 04:53.080 --> 04:58.150 And so here to make it simple, you can just create a list with different speeds. 04:58.150 --> 05:01.520 So five milliseconds, ten, 15, 20. 05:01.520 --> 05:08.480 And when you receive a message that the button has been pressed, you just go to the next speed, okay? 05:08.480 --> 05:10.850 And when you reach that one, you go back to the beginning. 05:10.850 --> 05:17.780 And so when you update actually the delay, well, that's going to also update this code because now 05:17.780 --> 05:21.770 you're going to check with the new action delay and you don't need to do anything else. 05:22.190 --> 05:22.670 All right. 05:22.670 --> 05:29.690 So to recap here, you do a sweep with Python, you send the servo command to the Arduino. 05:30.380 --> 05:30.790 Okay? 05:30.800 --> 05:38.930 And for that, you use a non-blocking structure and you also read from cell so that when you press on 05:38.930 --> 05:42.740 the push button, you send the message from Arduino to Raspberry Pi. 05:42.740 --> 05:49.640 And when you receive that message, you change the delay with one of the delay that is in that list. 05:49.730 --> 05:53.750 And I will see you in the next lesson for the solution.