WEBVTT 00:00.080 --> 00:06.320 Now that you have three LEDs and one pushbutton on your circuit, let's make a slightly bigger project. 00:06.350 --> 00:11.510 Note that if you found the previous activities quite simple, well, this one is going to be a bit more 00:11.510 --> 00:12.380 challenging. 00:12.380 --> 00:14.480 If you can't find the solution by yourself. 00:14.480 --> 00:19.460 Don't worry though, you can watch the solution and come back to it later to try again. 00:19.880 --> 00:24.440 So here is the result you should get for this challenge when you start the program. 00:24.440 --> 00:27.380 As you can see here, all the LEDs are powered off. 00:27.410 --> 00:34.190 Then when you press the button here, you can see the first LED is powered on and all the other ones 00:34.190 --> 00:35.570 are powered off. 00:35.600 --> 00:39.140 If I press again now, I switch to the second LED. 00:39.290 --> 00:44.000 So I turn off the first one and all the other ones and I turn on that one. 00:44.000 --> 00:47.780 I press again, we go to the third led and then I press again. 00:47.810 --> 00:50.240 We go back to the first, etc.. 00:50.330 --> 00:50.990 Okay. 00:50.990 --> 00:57.080 And one important thing here is that this action is only when I press on the button, okay? 00:57.110 --> 00:59.480 When I release, it doesn't do anything. 00:59.660 --> 01:03.500 Uh, it doesn't matter how long I press on the button, okay? 01:03.530 --> 01:07.140 It's just when I press on the button that we switch the LED. 01:08.460 --> 01:10.650 So that is your challenge. 01:10.650 --> 01:15.030 Now I'm going to give you a few tips, a few help to get started. 01:15.030 --> 01:22.140 So first of all, if I go back to the previous activity, you see we have this button that when pressed 01:22.170 --> 01:28.830 okay, this is going to register a function to call when the button is actually pressed okay. 01:28.860 --> 01:31.170 So you will follow a similar structure here. 01:31.170 --> 01:33.510 You will need to use the pose to pause the program. 01:33.510 --> 01:38.250 And before that you will register a function to call when the button is pressed. 01:38.250 --> 01:39.900 So for example you will have. 01:39.900 --> 01:42.870 So you will have to create the button and everything. 01:42.870 --> 01:50.400 And then you will do button when pressed is equal to and you will put a function. 01:50.460 --> 01:56.220 So for example here I'm just going to create a function named switch LED. 01:56.850 --> 02:01.140 Just like that I will write code in this later. 02:01.140 --> 02:04.560 And then you can write switch LED okay. 02:04.590 --> 02:06.780 And you don't put any parentheses. 02:06.780 --> 02:11.930 Once again you don't put the parentheses because otherwise this would call the function. 02:11.960 --> 02:15.290 Here you just want to give the name of the function. 02:15.320 --> 02:15.800 All right. 02:15.800 --> 02:22.730 And one more thing is that to keep track of which LED we are actually turning on, and the other ones 02:22.730 --> 02:23.690 will be turned off. 02:23.690 --> 02:30.230 We will add here I'm going to create a variable named LED index okay. 02:30.260 --> 02:32.480 That starts at zero. 02:32.480 --> 02:37.640 So you can use this variable to keep track of which LED is turned on okay. 02:37.670 --> 02:40.190 So for now we start and we start at zero. 02:40.190 --> 02:44.360 Because in Python as you already know, we start to count from zero. 02:44.360 --> 02:48.950 And in this function in the switch LED that's called whenever you press the button. 02:48.950 --> 02:54.590 What you can do is you can turn on whichever LED corresponds to the current index. 02:54.590 --> 02:57.140 And then you can increment this index. 02:57.140 --> 03:02.390 So you can add plus one for example, so that the next time the function is called again you can decide 03:02.390 --> 03:04.220 to turn on the next LED. 03:04.250 --> 03:04.580 All right. 03:04.580 --> 03:08.720 So with this tip you can start thinking about designing a solution. 03:08.720 --> 03:12.110 And just to finish here there's one thing you will need to do. 03:12.110 --> 03:18.150 So previously I have told you that you can use a variable here, a global variable inside a function. 03:18.150 --> 03:24.000 So you can definitely read this variable, meaning that you can print it, you can read it, you can 03:24.000 --> 03:24.510 use it. 03:24.510 --> 03:33.750 But if you want to modify this variable, if I want to do LED index is equal one for example this is 03:33.750 --> 03:39.420 going to give you an error okay when it reaches that line because well when you use a global variable 03:39.420 --> 03:41.160 inside a function you can read it. 03:41.160 --> 03:50.280 But in order to write to it you first have to use this global keyword plus the name of the variable. 03:50.280 --> 03:55.950 So we will start our switch LED function with global LED index. 03:55.950 --> 04:03.000 Because we will not only read this variable, we will not only use it, but we will also modify it. 04:03.030 --> 04:03.390 All right. 04:03.390 --> 04:05.280 So I'm just going to remove that. 04:05.280 --> 04:09.360 And this is basically the code that we will start from. 04:09.360 --> 04:13.860 So of course you need to do all the imports and initialize the LEDs and all that stuff. 04:13.860 --> 04:15.300 And now it's your time to practice. 04:15.300 --> 04:19.740 So make sure you spend enough time on this activity before you go to the solution, and I will see you 04:19.740 --> 04:21.030 in the next lesson.