WEBVTT 00:00.110 --> 00:03.080 Here is the solution for the activity number five. 00:03.080 --> 00:07.940 So I'm first going to do the solution with the code that we have seen previously. 00:07.940 --> 00:11.900 And then I'm going to give you two additional things that are very important. 00:11.930 --> 00:16.370 First is a way to improve the program and make it more efficient. 00:16.370 --> 00:21.920 And the second is well we're going to use a different way to write the program and that we will use 00:21.920 --> 00:24.650 directly for the next activity of this course. 00:24.650 --> 00:26.240 So let's get started. 00:26.240 --> 00:29.690 The first thing we need to do is to import stuff. 00:29.690 --> 00:34.160 So from Gpio zero import. 00:34.190 --> 00:41.660 So we need to import the LED and the button because we're going to use both so LED maybe you have written 00:41.660 --> 00:49.130 this from Gpio zero import like this import button. 00:49.130 --> 00:50.540 And that is correct okay. 00:50.570 --> 00:52.970 It's going to import the LED and the button. 00:52.970 --> 00:56.840 But what we can also do is to add a comma. 00:56.870 --> 01:00.810 So I showed you that before we can add a comma and just do button. 01:00.840 --> 01:01.290 Okay. 01:01.290 --> 01:08.460 So from library import functionality, one comma functionality two comma etc.. 01:08.490 --> 01:08.820 Great. 01:08.820 --> 01:12.900 So now I will initialize my LED just like that. 01:12.900 --> 01:23.340 So LED I put the Gpio number 17 and then button I put button and the Gpio number 26. 01:23.550 --> 01:30.930 So first things first we initialize the Gpio 17 and we initialize the Gpio 26. 01:30.960 --> 01:32.910 And then we want to detect. 01:32.910 --> 01:36.420 So when the button is pressed we power on the LED. 01:36.540 --> 01:39.780 If it's not pressed while the LED is going to be turned off. 01:39.780 --> 01:46.530 And I don't want to just do that one time here when we run the program, I want to do it continuously. 01:46.530 --> 01:50.160 So I'm also going to use this while true loop. 01:50.160 --> 01:51.780 So an infinite loop. 01:51.780 --> 01:59.650 And I'm going to say simply if button dot is pressed I'm going to put a colon. 01:59.650 --> 02:01.240 And if it's true. 02:01.270 --> 02:04.450 Well, we do led dot on. 02:05.350 --> 02:08.680 If it is not true then I'm going to go back here. 02:08.680 --> 02:11.920 So if it's not true it can only be false. 02:11.950 --> 02:17.260 So I'm going to put else and then led dot of okay. 02:17.290 --> 02:19.450 And pay attention to the indentation here. 02:19.480 --> 02:25.480 The whole if is with one indentation because it's inside the while. 02:25.510 --> 02:31.870 But then for example that instruction has one indentation of four spaces plus an extra one. 02:31.870 --> 02:34.150 And now I can test my program. 02:34.150 --> 02:37.300 So let's just run it okay. 02:37.330 --> 02:38.080 It's running. 02:38.080 --> 02:40.360 So there's nothing printed here but it's running. 02:40.360 --> 02:42.760 And I can just press on the push button. 02:42.760 --> 02:47.050 You see the LED is on now I release okay. 02:47.080 --> 02:49.000 And you can see when it pressed it's on. 02:49.000 --> 02:54.760 When it's released it's off on off on off etc.. 02:54.760 --> 02:55.870 So that's working. 02:55.870 --> 03:00.770 And if you have written this code, well you have solved the activity, but now I'm going to show you 03:00.770 --> 03:02.180 something additional. 03:02.180 --> 03:03.560 So actually two things. 03:03.560 --> 03:05.390 Let's start with the first one. 03:05.390 --> 03:09.350 And the first one is about optimizing the program a bit. 03:09.350 --> 03:11.600 And why do I care about optimizing here. 03:11.600 --> 03:13.310 Because I'm going to show you something. 03:13.310 --> 03:22.760 So while the program is running you can go here and search for it's going to be the task manager here. 03:24.830 --> 03:25.490 Okay. 03:25.490 --> 03:29.180 And let's wait that it initializes okay. 03:29.210 --> 03:33.080 And you can see we have here a command Python three. 03:33.080 --> 03:35.120 So that's basically the program that's running. 03:35.270 --> 03:36.530 You can ignore the rest. 03:36.530 --> 03:41.930 And you can see that this Python three command is taking 25% of the CPU. 03:41.930 --> 03:43.160 And what does that mean. 03:43.160 --> 03:48.590 So actually on the Raspberry Pi here on the Raspberry Pi five I have four CPUs. 03:48.590 --> 03:54.740 And when you run a Python script it's going to run using one CPU unless you have a multi-threaded application. 03:54.740 --> 03:56.210 But that's way more complex. 03:56.210 --> 04:03.120 And for now it's just using one CPU, so when you see 25%, it means that the program is actually using 04:03.120 --> 04:04.320 the whole CPU. 04:04.320 --> 04:08.250 So a program as simple as this is using the whole CPU. 04:08.280 --> 04:09.420 Why is that? 04:09.450 --> 04:10.080 Why is that? 04:10.080 --> 04:14.940 Because well, we have an infinite loop that just runs at full speed. 04:14.940 --> 04:22.140 And if it runs at full speed, it's basically going to run as fast as it can and use 100% of the resources 04:22.140 --> 04:24.180 of one CPU. 04:24.180 --> 04:25.440 So we want to avoid that. 04:25.440 --> 04:26.010 For what? 04:26.040 --> 04:26.910 For a few reasons. 04:26.910 --> 04:30.000 First, it's going to make your Raspberry Pi heat more. 04:30.000 --> 04:34.920 So if you don't have any fan or anything to protect from the heat, well, it's going to heat quite 04:34.920 --> 04:35.430 a lot. 04:35.460 --> 04:41.040 Not necessarily a problem, but well, you don't want to have your Raspberry Pi too hot and then while 04:41.040 --> 04:42.780 you are using one full CPU. 04:42.780 --> 04:45.810 So anything else that you run is going to be slower. 04:45.810 --> 04:49.410 And if there is an easy way to solve that, then we're going to do it. 04:49.650 --> 04:53.280 So instead of running this full speed, we don't need to run this full speed. 04:53.310 --> 05:00.130 We could add a small delay actually between each iteration of the while loop. 05:00.160 --> 05:02.890 I'm going to add here I'm going to import time. 05:02.980 --> 05:08.200 And what I can do is after I read the button, I'm going to add. 05:08.200 --> 05:09.850 So I go back to this indentation. 05:09.880 --> 05:10.060 Okay. 05:10.090 --> 05:13.060 After the if time dot sleep. 05:13.060 --> 05:15.910 And let's actually pause the program. 05:15.910 --> 05:21.070 But for a very short time for example 0.01 second. 05:21.070 --> 05:22.660 So that's very very tiny. 05:22.660 --> 05:25.360 That's basically ten milliseconds. 05:25.360 --> 05:27.310 So you will not see that okay. 05:27.340 --> 05:32.830 When you run the program you will not see any difference because we as human, we well, we can't see 05:32.860 --> 05:35.020 a ten millisecond difference in the program. 05:35.020 --> 05:36.910 So it's going to do the exact same thing. 05:36.910 --> 05:44.080 But this loop is going to be running at a much, much slower speed, which is still high enough for 05:44.080 --> 05:44.830 this application. 05:44.830 --> 05:48.310 So now let's stop and let's run this again. 05:48.310 --> 05:51.460 Now you can well, you can press the push button again. 05:51.460 --> 05:54.100 This is going to be exactly the same thing. 05:54.100 --> 05:58.700 But if we have a look at our task manager again. 05:59.270 --> 06:04.370 So let's wait a few seconds for that initialization. 06:04.370 --> 06:06.350 And Python three is here. 06:06.350 --> 06:08.240 And now it's using zero. 06:08.240 --> 06:11.330 So not 0% but zero point something percent. 06:11.330 --> 06:20.390 So you see we went from 100% of one CPU to something that's very very very tiny okay. 06:20.450 --> 06:23.600 So this improvement is actually quite important. 06:23.600 --> 06:30.980 If you run an infinite loop like this for a program that you run on Raspberry Pi, it's better if this 06:30.980 --> 06:33.710 loop is going to run at full speed. 06:33.710 --> 06:41.180 So the full CPU speed is better to slow it down a bit by adding here a time.sleep with a small amount. 06:41.180 --> 06:45.320 And basically this is ten milliseconds, so it's 0.01 second. 06:45.350 --> 06:51.920 That means that you are going to run this at about 100 times per second. 06:51.950 --> 06:52.130 Okay. 06:52.160 --> 06:53.090 So that's still a lot. 06:53.120 --> 06:54.470 And we are talking here about. 06:54.470 --> 06:56.550 So if it's 100 times per second. 06:56.550 --> 07:01.140 We also talk about a loop that runs at 100Hz. 07:01.140 --> 07:03.180 So that's for the technical terms. 07:03.180 --> 07:10.230 And one thing is maybe I'm gonna just put that at the beginning of the loop. 07:10.230 --> 07:12.120 It doesn't really change anything okay. 07:12.150 --> 07:16.620 I just put it at the beginning so that I don't forget it later if I have more code. 07:16.620 --> 07:21.450 And also well, as I add code, maybe I'm going to mess up the indentation for that. 07:21.450 --> 07:26.460 So here I make sure that it's at the beginning of the loop and it's going to slow the loop. 07:26.460 --> 07:29.490 So we run it at 100 times per second. 07:29.520 --> 07:29.880 Great. 07:29.880 --> 07:31.020 Let me stop that. 07:31.020 --> 07:33.720 And now I want to show you something else. 07:33.720 --> 07:36.720 So that's not related to optimization or anything. 07:36.720 --> 07:42.900 It's just that we are going to use another functionality from the Gpio library to do actually the exact 07:42.900 --> 07:47.250 same thing, but the code is going to be much smaller. 07:47.250 --> 07:50.460 And that's the code we are going to use also for the next activity. 07:50.460 --> 07:55.450 So first, that was actually a very good practice for you to work on loops and conditions. 07:55.480 --> 07:57.160 Okay, so that's why I kept it like this. 07:57.160 --> 08:00.040 And now let's see how we can write this code differently. 08:00.070 --> 08:06.280 So what I'm going to do is I'm going to comment that like this comment. 08:06.280 --> 08:07.900 So we don't execute it. 08:07.900 --> 08:12.310 And there is in fact inside this button functionality. 08:12.340 --> 08:14.740 What we can do is just write button. 08:14.740 --> 08:21.400 So using this button here dot when pressed is equal to. 08:21.430 --> 08:24.700 And then just give a function here. 08:24.700 --> 08:27.730 So for example led dot on. 08:27.730 --> 08:31.840 And note that we don't provide any parentheses. 08:31.870 --> 08:34.120 Okay I'm gonna explain that just in one minute. 08:34.120 --> 08:38.950 So we can say that when the button is pressed when pressed we're going to turn the LED on. 08:38.950 --> 08:46.180 And then we can also do button dot when released LED dot off. 08:46.360 --> 08:48.850 And so this line is actually not going to stop. 08:48.850 --> 08:54.380 It's just going to register here this this function and this one as well. 08:54.380 --> 08:59.420 So if we just run the program like this, well it's going to run and then it's going to exit. 08:59.420 --> 09:00.950 So it's not going to do anything. 09:00.950 --> 09:05.270 So we need to somehow pause the program. 09:05.270 --> 09:08.720 We need to find a way to pause the execution of the program. 09:08.720 --> 09:12.830 And for this we can do from signal. 09:12.830 --> 09:16.730 So that's another library you can use import pause. 09:16.760 --> 09:23.360 You have the pause function from the signal library that we can just use at the end of our program here. 09:23.570 --> 09:26.090 Pause like that with parenthesis. 09:26.120 --> 09:26.450 All right. 09:26.450 --> 09:29.090 So what do we do here is we initialize the LED the button. 09:29.090 --> 09:32.660 And then we say that when the button is pressed we're going to turn on the LED. 09:32.660 --> 09:34.880 When the button is released we turn off the LED. 09:34.880 --> 09:36.470 And then we pause the program. 09:36.470 --> 09:43.820 And just to give you more details about this, well, this is what we can call a callback function. 09:43.820 --> 09:50.420 So to use a real life analogy, let's say that you need some information from somebody and they will 09:50.420 --> 09:53.850 tell you, okay, I will call you back when I have this information. 09:53.850 --> 09:57.510 So you give them your, for example, your phone number or your email. 09:57.540 --> 09:57.780 All right. 09:57.810 --> 10:01.170 So you kind of we're going to talk about registering your phone number. 10:01.170 --> 10:07.860 So you register your phone number so that when they have this information they can call you back using 10:07.860 --> 10:08.850 this phone number. 10:08.880 --> 10:09.090 Okay. 10:09.090 --> 10:10.380 So here there are two things. 10:10.380 --> 10:15.330 One is that there is an event that must happen and that is external. 10:15.510 --> 10:17.250 You don't really know when it's going to happen. 10:17.250 --> 10:18.600 It might happen at some point. 10:18.600 --> 10:22.800 And when this event is happening you want to be called back. 10:22.800 --> 10:25.080 So you want to be notified of this. 10:25.080 --> 10:26.970 And that's exactly what's happening here. 10:27.000 --> 10:30.150 You see we have this dot when pressed. 10:30.150 --> 10:33.600 So this is the external event when the button is pressed. 10:33.600 --> 10:36.150 But you don't know when the button is going to be pressed from the program. 10:36.180 --> 10:36.360 Okay. 10:36.390 --> 10:38.370 That's an external event. 10:38.400 --> 10:42.270 And so you register a callback and the callback is led1. 10:42.270 --> 10:47.460 So when the button is pressed here is what to do, what to call. 10:47.460 --> 10:50.520 And we're going to call this function led1. 10:50.520 --> 10:57.730 And just note it's one particular thing about callbacks is that you don't provide the parentheses, 10:57.730 --> 11:00.880 because if you provide a parentheses, you are calling the function right. 11:00.910 --> 11:05.530 Now here you are registering the function so it can be called later. 11:05.530 --> 11:11.890 So basically with this you just register those two functions that they can be called when this event 11:11.890 --> 11:14.530 or that event is happening. 11:14.560 --> 11:16.360 And then you make sure you pause the program. 11:16.360 --> 11:20.920 Because if you don't pause the program well it's just going to exit and nothing is going to happen. 11:20.920 --> 11:25.990 And now you can try to run this and it's going to be the exact same behavior as what we had before. 11:26.020 --> 11:26.530 All right. 11:26.530 --> 11:28.960 And you can see the code is much smaller actually. 11:28.960 --> 11:31.840 We don't even need the time library anymore. 11:31.840 --> 11:37.570 And if you look at if we go back to the task manager here, you will see that. 11:37.600 --> 11:43.210 So this is running and uh, well this is not using much CPU as well. 11:43.240 --> 11:43.420 Okay. 11:43.420 --> 11:46.000 So this code is already pretty much optimized. 11:46.000 --> 11:48.340 We don't need to add any time.sleep here. 11:48.370 --> 11:48.700 All right. 11:48.700 --> 11:51.820 And I will come back to this for the next activity of this course.