WEBVTT 00:00.080 --> 00:05.030 This is step number three of the final project of the intercom system. 00:05.030 --> 00:11.240 And now that we have initialized all the hardware components on the Arduino, we're going to write the 00:11.240 --> 00:18.020 code so we can send the output messages to the Raspberry Pi when we have something that happens with 00:18.020 --> 00:18.560 the hardware. 00:18.560 --> 00:23.210 So actually here we have just the button code to write. 00:23.450 --> 00:29.570 So first of all, I'm going to save this as intercom step three. 00:29.780 --> 00:30.410 Okay? 00:31.160 --> 00:31.460 Okay. 00:31.490 --> 00:32.150 Save. 00:32.660 --> 00:36.710 And let's actually open again the protocol that we have written here. 00:36.740 --> 00:39.050 So from it's right there. 00:40.340 --> 00:46.760 So we can see here from Arduino to Raspberry Pi, we just have the button pressed command to send with 00:46.760 --> 00:47.600 backslash n. 00:47.630 --> 00:49.550 So that's what we are going to do. 00:51.560 --> 00:52.100 And so. 00:52.100 --> 00:56.300 Well, this we have already done that before, but I'm still going to do it again. 00:56.630 --> 01:02.060 Right there is to read from the push button and detect when we have pressed on the push button. 01:02.240 --> 01:06.740 So I'm going to create a 2 or 3 new variables here. 01:07.070 --> 01:10.900 Let's do that right there as a global variables. 01:10.910 --> 01:20.360 So unsigned long last time button changed with equal to millis or zero, it doesn't matter. 01:20.360 --> 01:26.090 And unsigned long debounce delay. 01:26.090 --> 01:28.550 Let's put 50 milliseconds. 01:28.580 --> 01:33.350 You can adjust that a bit more, a bit less depending on how it works with your circuit. 01:33.620 --> 01:36.380 So this is going to be for the Debounce mechanism. 01:36.590 --> 01:45.230 And then I'm going to also add byte previous button state and the previous button state. 01:45.230 --> 01:56.600 I initialize it here, previous button state is equal to digital read from the button pin. 01:56.610 --> 02:04.650 And of course I do that after I have put the pin mode with button pin input now in the void loop. 02:06.240 --> 02:12.300 So in the void loop, we can read from the push button, but before we read from the push button, we're 02:12.300 --> 02:15.870 going to do the Debounce mechanism to be sure we can read from the push button. 02:15.870 --> 02:21.420 So unsigned long time now is equal to millis. 02:21.420 --> 02:27.150 So we get the time every well, every time we enter the void loop, which is going to be pretty fast. 02:27.990 --> 02:37.110 If so, if the current time time now minus the last time the button state has changed here is greater 02:37.110 --> 02:41.340 or equal then the debounce delay. 02:42.920 --> 02:49.520 So if we have spent enough time since the button has changed for the last time, then we can read the 02:49.520 --> 02:50.570 button state. 02:51.290 --> 02:58.940 So bite button state is equal to digital read button pin. 02:59.480 --> 03:02.950 And then we can compare the button state. 03:02.960 --> 03:06.110 So the current one we read from the previous one. 03:06.110 --> 03:08.570 So from previous button state. 03:08.600 --> 03:14.360 If those are different, then we have either pressed or released the button. 03:14.360 --> 03:18.920 And in that case, first we can update this. 03:19.130 --> 03:22.160 So the last time the button has changed is actually now. 03:22.160 --> 03:23.330 So we put time. 03:23.330 --> 03:29.180 Now we also say that the previous button state is the current one for the next time we enter the void 03:29.180 --> 03:29.720 loop. 03:31.010 --> 03:38.330 And then we can do an action so we can check if, for example, button State is equal to high, which 03:38.330 --> 03:44.470 means that we have pressed on the button because we have a pull down resistor. 03:44.480 --> 03:47.180 And if it's low, we have just released the button. 03:47.180 --> 03:55.060 But here we want to know when we press on the button and once we have this, we can send to sales. 03:55.060 --> 03:59.240 So send the message to sale and to send the message to sale. 03:59.270 --> 04:01.490 I'm going to initialize sale here. 04:02.210 --> 04:04.250 Serial dot. 04:04.250 --> 04:07.400 Begin with this baud rate. 04:07.400 --> 04:09.530 We're going to use the same in the Raspberry Pi. 04:09.770 --> 04:18.260 Let's do while not serial okay for compatibility with some Arduino boards and here I'm going to add 04:18.260 --> 04:23.810 something else that I didn't do before and we probably won't need it in that project, but that can 04:23.810 --> 04:29.930 be a good best practice to add it to the while serial dot available. 04:31.240 --> 04:33.400 Is greater than zero. 04:34.030 --> 04:38.260 You do serial dot read. 04:38.590 --> 04:41.640 So read is going to read only one byte. 04:41.650 --> 04:43.930 So here we just read it and we don't store it. 04:43.960 --> 04:45.370 We don't do anything with it. 04:45.370 --> 04:49.390 But basically what we do here is we just clear the input buffer. 04:49.630 --> 04:55.900 If you remember with Serial in Python, you have the reset input buffer function. 04:55.900 --> 05:03.280 We don't have one in Arduino, but we can easily implement it by just checking that well, while we 05:03.280 --> 05:08.140 still have bytes on the input buffer, we read them so we clear them from the buffer. 05:08.230 --> 05:13.480 So we are sure that when we start here we don't have anything in the input buffer. 05:13.690 --> 05:17.950 And so I said for this project is not going to be useful because why is that? 05:17.980 --> 05:24.100 Because when we start the Python program and we initialize the communication with the Arduino, well, 05:24.100 --> 05:26.320 the Arduino is going to be ready first. 05:26.320 --> 05:33.770 So by the time that we enter this block of code and that we enter the void loop, the Python program 05:33.770 --> 05:36.980 is still not going to be sending data. 05:37.010 --> 05:37.430 Okay? 05:37.430 --> 05:44.060 So this is should not be called, but that can be a best practice for other projects of your own. 05:44.120 --> 05:44.600 Okay. 05:44.600 --> 05:50.420 If you want to make different boards communicate between each other and now that the cell is initialized, 05:50.420 --> 05:55.520 let's actually do here serial dot print. 05:55.570 --> 06:02.600 Ln okay, because we need the backslash n at the end button pressed exactly like that. 06:02.810 --> 06:04.580 This should be it. 06:04.580 --> 06:05.600 Let's check. 06:06.260 --> 06:09.680 So we have those three variables here. 06:10.100 --> 06:14.210 We correctly initialize the state for the button. 06:14.210 --> 06:15.920 We read the previous state. 06:16.130 --> 06:22.520 We have the serial initialization and then we read from the push button with the debounce mechanism. 06:22.520 --> 06:26.000 And when the button is pressed, we send button pressed. 06:26.010 --> 06:29.600 Let's connect the Arduino. 06:31.340 --> 06:34.690 Okay, let's now so it's good. 06:34.690 --> 06:44.380 Let's now upload the code and well, actually I have forgotten so just made a typo here. 06:47.980 --> 06:50.440 Uploading down, uploading. 06:50.440 --> 06:54.790 Let's open the serial monitor and I'm going to press on the push button. 06:54.790 --> 06:57.310 So starting pressing the push button. 06:57.310 --> 06:59.530 Button pressed button pressed button pressed. 06:59.530 --> 07:05.290 So every time I press, I receive a button pressed message on the serial monitor. 07:05.410 --> 07:07.120 Everything is correct. 07:07.120 --> 07:08.530 And that's the end of this. 07:08.530 --> 07:15.040 Step number three, we can now focus on the input comments that we receive from the Raspberry Pi.