WEBVTT 00:00.080 --> 00:05.900 Let's now see how to read data from the push button and more specifically, how to know when we have 00:05.900 --> 00:07.130 pressed on the button. 00:07.130 --> 00:10.160 So the exact moment when we have pressed on the button. 00:10.190 --> 00:14.960 This is something you should already know how to do as per the prerequisites of the course, but I'm 00:14.960 --> 00:16.520 still going to do it quickly. 00:16.520 --> 00:17.480 As a recap. 00:17.480 --> 00:19.880 Also, we will debounce the button. 00:19.880 --> 00:26.600 So first of all, what you're going to do is to create a define here button. 00:27.680 --> 00:30.020 So define a constant int. 00:30.020 --> 00:32.990 And so the pin is number seven. 00:33.650 --> 00:42.170 And then if you want to initialize the push button, you do pin mode with button pin and then input. 00:42.470 --> 00:44.600 So the push button is initialized. 00:44.630 --> 00:53.360 Now if you want to read from the push button, you are going to do digital read button pin and this 00:53.360 --> 00:55.850 is going to return you a byte. 00:55.880 --> 00:58.370 Okay, that is high or that is low. 00:58.370 --> 01:03.710 So for example, bytes state is equal to digital read button pin. 01:04.070 --> 01:09.860 Now if we want to check if we have pressed on the push button, what we need to do is we need to save 01:09.860 --> 01:10.700 the previous state. 01:10.700 --> 01:15.920 So we need to read the state, save the previous state, and then read again and check if we have something 01:15.920 --> 01:16.460 different. 01:16.490 --> 01:16.940 Okay. 01:16.940 --> 01:26.420 So I'm going to add here, byte previous button state, and I'm simply going to initialize that here 01:26.600 --> 01:31.130 to the current state of the button just after we initialize it. 01:31.130 --> 01:33.680 So that will be the first state of the push button. 01:33.680 --> 01:39.110 And so now what we need to do in the for loop is to read the push button again with digital read and 01:39.110 --> 01:43.360 then compare to the previous button state and see if we have something different. 01:43.370 --> 01:49.610 But what I'm also going to do is I'm going to debounce the push button because if we just compare the 01:49.610 --> 01:54.890 previous and the current state, what's going to happen is we're going to have the bounce mechanism. 01:54.890 --> 02:00.260 So the physical bounce of the button and this will give us some wrong measurements. 02:00.350 --> 02:00.750 Okay. 02:00.750 --> 02:07.650 So we need to debounce the button to make sure that when we actually press, we get just one press on 02:07.650 --> 02:11.640 the code and not multiple prices because the button is bouncing. 02:11.640 --> 02:16.440 So to do that, I'm going to create two new variables here. 02:16.740 --> 02:23.430 Unsigned long last time button pressed is equal to. 02:23.460 --> 02:25.500 So let's initialize to millis or to zero. 02:25.500 --> 02:26.460 It doesn't matter. 02:26.460 --> 02:36.060 And then unsigned long let's say button debounce is equal to and let's put 50 milliseconds. 02:36.060 --> 02:41.730 So what we're going to do here, basically we're going to first in the void loop, get the time. 02:41.730 --> 02:47.130 So unsigned long time now is equal to millis. 02:47.430 --> 02:56.430 And then we are going to do if time now minus last time the button has been pressed if this is greater 02:56.430 --> 03:02.280 or equal than the button debounce duration here, then we can enter this. 03:02.310 --> 03:07.770 If so, we will see that when the state of the button changes, we're going to update the last time 03:07.770 --> 03:13.740 the button was pressed to the current time and so that the next time we enter the void loop, we're 03:13.740 --> 03:14.910 going to check the condition. 03:14.910 --> 03:18.090 So time now minus last time the button has been pressed. 03:18.090 --> 03:20.970 And if this is lower than the delay. 03:20.970 --> 03:27.090 So basically, if this is lower than 50 milliseconds, then we are not going to read the state again. 03:27.090 --> 03:32.940 So basically we are going to ignore the button for 50 milliseconds every time the button has been pressed 03:32.940 --> 03:35.910 so we don't read all the bounces of the button. 03:35.910 --> 03:41.370 So now if enough time has passed, what we can do is do bite button state. 03:41.370 --> 03:47.220 So the current one is equal to digital read with button pin. 03:49.200 --> 03:49.980 Like this. 03:50.790 --> 03:59.640 We read the button state and then we do if Button State is different from the previous button state. 03:59.910 --> 04:03.930 In that case, we know that the state has changed. 04:04.080 --> 04:10.110 And what we can do is to now update the last time the button pressed. 04:10.110 --> 04:11.970 So actually let's name it different. 04:11.970 --> 04:14.940 Last time button changed. 04:14.970 --> 04:15.480 Okay. 04:15.990 --> 04:23.100 Because it's not pressed here, it's just changed because if we are here, it could be pressed or released. 04:23.100 --> 04:25.980 So I'm just going to use changed, which is for both. 04:25.980 --> 04:26.190 Okay. 04:26.190 --> 04:29.700 So last time the button has changed is actually time now. 04:29.850 --> 04:30.240 Okay. 04:30.240 --> 04:32.550 Because that's what just happened. 04:32.550 --> 04:39.030 And also I'm going to update the previous button state, which is now the current button state. 04:39.180 --> 04:45.090 And so the next time we enter the void loop, we're going to first check if enough time has passed since 04:45.090 --> 04:46.800 the last time button changed. 04:46.800 --> 04:55.390 And we only going to enter this if again after 50 milliseconds and then well, when we are here in the 04:55.390 --> 04:58.600 code, we know that the button state has changed. 04:58.600 --> 05:03.340 So to know if the button has actually been pressed or released, we do. 05:03.370 --> 05:12.040 If button State is equal to high in our case because we have a pull down resistor, this means that 05:12.040 --> 05:17.500 the button has been pressed and if it's low, it means the button has been released. 05:17.500 --> 05:18.940 So here we could do so. 05:18.940 --> 05:22.120 Let's actually do sale dot begin. 05:22.690 --> 05:30.480 So here we use sale to debug and serial dot print. 05:30.580 --> 05:35.410 Ln let's say button has been pressed. 05:35.830 --> 05:42.280 So when we enter this, if we know that the button has been pressed, so just pressed and we don't have 05:42.280 --> 05:48.460 any bounds because the next time we are going to read the button is 50 milliseconds later. 05:48.460 --> 05:50.920 So let's upload the code. 05:52.270 --> 05:54.140 And actually, we have an error. 05:54.160 --> 05:55.420 Why do I have this error? 05:55.450 --> 06:01.690 You can see can't open device because I have simply not plugged my Arduino to the Raspberry Pi or to 06:01.690 --> 06:02.260 the computer. 06:02.260 --> 06:04.780 If you are using your normal computer. 06:04.780 --> 06:06.580 And now check tools. 06:06.940 --> 06:07.630 Okay. 06:07.630 --> 06:08.560 Upload. 06:10.490 --> 06:11.750 And done uploading. 06:11.750 --> 06:13.580 I'm going to open the serial monitor. 06:13.610 --> 06:17.000 Make sure the border is correct and I'm going to press on. 06:17.000 --> 06:19.400 The push button button has been pressed. 06:19.520 --> 06:19.760 Okay. 06:19.880 --> 06:20.720 Press again. 06:20.720 --> 06:22.820 And you can see every time I price. 06:22.820 --> 06:30.260 So price again button has been pressed one more time and well, the code is working. 06:30.680 --> 06:37.250 So this is the structure that you are going to use often to know when you have pressed or released on 06:37.250 --> 06:40.490 a push button and with the debounce mechanism.