1 00:00:00,720 --> 00:00:07,630 Like in this example, I'm going to show you how to read the state of a button using a hardware timer. 2 00:00:08,010 --> 00:00:14,310 Just remind you that in the previous two variations of the same exercise, you learned how to read the 3 00:00:14,310 --> 00:00:18,870 state of a button using an infinite loop, like in this example right here. 4 00:00:19,230 --> 00:00:23,910 And also how to use a hardware interact as in this example here. 5 00:00:24,600 --> 00:00:32,910 The example in which I'm using the hardware timer is really a variation of the hardware in the example. 6 00:00:33,240 --> 00:00:39,630 And you ought to know how to use the hardware timer from an earlier example with reality, which you 7 00:00:39,630 --> 00:00:46,920 can see here in this script as we have defined the time down here and lines three, four and thirty 8 00:00:46,920 --> 00:00:47,370 five. 9 00:00:47,670 --> 00:00:54,360 So in this lecture, basically taking these scripts and putting them together and creating a hybrid 10 00:00:54,360 --> 00:00:55,510 that looks like this. 11 00:00:56,070 --> 00:01:03,480 So what's happening here is that I've got a timer which has a period of 50 milliseconds and this is 12 00:01:03,480 --> 00:01:04,530 a periodic timer. 13 00:01:04,530 --> 00:01:11,430 So it fires every 50 milliseconds and each time it fires, it will call the interruption of this routine 14 00:01:11,640 --> 00:01:16,710 called button on this compressed and this call ISO, which is right here. 15 00:01:17,130 --> 00:01:20,400 What it does is to check the state of the button. 16 00:01:20,400 --> 00:01:24,540 And if it is pressed, then it will update these variables here. 17 00:01:24,930 --> 00:01:33,330 At the same time, we've got the while loop infinite loop constantly checking for the value stored inside 18 00:01:33,330 --> 00:01:35,700 the global pattern and this compressed variable. 19 00:01:35,700 --> 00:01:41,520 And if it is true, then it will turn on the LCD and wait here for a second. 20 00:01:42,030 --> 00:01:48,270 It's a very it's a very simple way of going about reading the state of a button, taking advantage. 21 00:01:48,270 --> 00:01:55,320 Had we interrupt in terms of efficiency, I'm not quite sure which of these two is more efficient is 22 00:01:55,320 --> 00:01:56,400 hard really to say. 23 00:01:56,580 --> 00:02:02,490 I would say that the hardware interrupted is perhaps more efficient from the point of view that you 24 00:02:02,490 --> 00:02:12,360 don't occupy a hardware timer to keep firing every 15 milliseconds and calling the interrupt service 25 00:02:12,510 --> 00:02:13,170 routine. 26 00:02:13,510 --> 00:02:20,490 In this example here with the hardware interrupt, the ISI is only called when the button is actually 27 00:02:20,490 --> 00:02:21,000 pressed. 28 00:02:21,450 --> 00:02:29,970 But in this example here, I thought that this our way of using the hardware timer is interesting and 29 00:02:29,970 --> 00:02:32,400 worthwhile dedicating a lecture for it. 30 00:02:33,240 --> 00:02:34,980 Let's have a quick look at the beginning. 31 00:02:35,400 --> 00:02:36,840 There's nothing new really here. 32 00:02:36,840 --> 00:02:43,920 We import the appropriate functions from the machine in time modules, define the ality, define the 33 00:02:43,920 --> 00:02:46,020 button with its pull up resistor. 34 00:02:46,380 --> 00:02:54,210 We've got our button pressed variable, the interrupt service routine with a global keyword so that 35 00:02:54,210 --> 00:03:00,300 the button pressed and button event variables are global and then we can make changes to those variables 36 00:03:00,300 --> 00:03:01,800 from inside the ISO. 37 00:03:02,550 --> 00:03:10,080 Then when the ISI is called, we check for the value of the button and if it is down there, meaning 38 00:03:10,080 --> 00:03:16,140 that button is pressed so the value returned by value is going to be false or zero. 39 00:03:16,500 --> 00:03:25,650 Remember that of got this wire here which grounds the button value when it's pressed and therefore GPL 40 00:03:26,070 --> 00:03:32,390 four will read a low value or false value in the python speak. 41 00:03:32,790 --> 00:03:34,080 So Button is pressed. 42 00:03:34,080 --> 00:03:36,330 In this case, you apply the variables. 43 00:03:36,330 --> 00:03:43,020 We also store the event object in the event variable. 44 00:03:43,380 --> 00:03:45,750 Otherwise button is false. 45 00:03:46,560 --> 00:03:55,440 And notice that I have declared the button, pressed the function before I create the end, initialize 46 00:03:55,440 --> 00:04:01,590 the hardware timer because I need to pass it to the timer via this callback parameter. 47 00:04:02,040 --> 00:04:08,670 And if I call the ISO before it's actually declared, you're going to get an error message by the compiler 48 00:04:08,970 --> 00:04:11,820 when you try to compile and run the script. 49 00:04:12,600 --> 00:04:19,080 After that, we've got the while true, which constantly checks for the value stored in the button on 50 00:04:19,080 --> 00:04:25,300 this compressed file and then it just turns on reality and keeps it on for one second. 51 00:04:25,320 --> 00:04:26,400 Otherwise, it will turn it off. 52 00:04:27,600 --> 00:04:28,170 All right. 53 00:04:29,280 --> 00:04:35,880 So I'm going to make a copy of this script onto the device. 54 00:04:35,920 --> 00:04:39,630 I will call it button for time. 55 00:04:39,630 --> 00:04:41,610 I thought he y. 56 00:04:43,810 --> 00:04:45,790 And let's run it. 57 00:04:50,130 --> 00:04:50,600 OK. 58 00:04:53,900 --> 00:05:01,220 And it stays on for one second and you can see the event with it, we're passing and printing out here, 59 00:05:01,580 --> 00:05:07,520 starting the button and it's called event variable, which is created up here. 60 00:05:07,580 --> 00:05:14,960 And it's really its origins are the event parameter that is passed by the time I had with him up to 61 00:05:14,960 --> 00:05:16,090 the ISO. 62 00:05:16,490 --> 00:05:19,100 And when you print out, this is what you get. 63 00:05:20,120 --> 00:05:25,370 Okay, so that's about it with a button, you know, enough now to be able to use buttons in your sketches. 64 00:05:25,910 --> 00:05:31,820 Now there's one more lecture in this section, which is the next one in which I'll show you how to use 65 00:05:31,820 --> 00:05:36,320 a particular mirror and make use of the analog to digital converter.