WEBVTT 00:00.180 --> 00:05.940 Now that you have added ultrasonics insult to your in a secret, let's understand a few things about 00:05.940 --> 00:12.630 it and how it works so we can better understand then how to control it in the original code. 00:12.870 --> 00:15.240 So what does the ultrasonic sensor do? 00:15.510 --> 00:21.120 Well, it will measure a distance from an object on a wall that is in front of the sensor. 00:21.330 --> 00:31.080 OK, so here we are using the HTC as our four sensor and here are the practical characteristics of the 00:31.080 --> 00:31.550 sensor. 00:31.570 --> 00:36.530 So the characteristic you need to know in order to use it correctly. 00:36.960 --> 00:43.710 So the range of the sensor is between two centimetre and 400 centimeter, which means that, as you 00:43.710 --> 00:51.540 can see here on this diagram, you can start measuring objects and obstacles from two centimeters away 00:51.540 --> 01:00.810 from the sensor up to about four meter here, which is about one hundred and fifty something inches. 01:00.900 --> 01:09.930 If you need the conversion to whatever is to close from the sensor, less than two centimeter will not 01:09.930 --> 01:14.260 be measured and whatever is too far will not be measured either. 01:14.530 --> 01:18.630 OK, then you have the measuring angle, which is 15 degrees. 01:18.670 --> 01:22.340 OK, so on this diagram, it's not exactly 15 degrees. 01:22.370 --> 01:26.280 OK, just so you can understand, but you can see the angle. 01:26.280 --> 01:32.590 So everything which is below that angle or above that angle will not be measured. 01:32.970 --> 01:37.830 So the sensor, as you can see, will measure mostly what is in front of it. 01:37.860 --> 01:44.500 OK, you don't need to remember 15 degrees, just that the sensor will measure what is in front of it. 01:44.520 --> 01:46.420 OK, not on the side of the sensor. 01:46.500 --> 01:52.050 OK, mostly what's in front and from two centimeter to four meters. 01:52.350 --> 01:59.400 And so it's not uncommon in a robot, for example, a mobile robot to have multiple of those sensors. 01:59.580 --> 02:04.950 OK, we can have different sensors for different angles of the robots and different positions. 02:05.420 --> 02:07.680 Now, how does it work? 02:07.680 --> 02:08.460 Very quickly. 02:09.060 --> 02:12.160 So you don't need to understand everything that is written here. 02:12.930 --> 02:16.430 This is just the diagram from the sensor data sheet. 02:16.800 --> 02:19.110 So here, what are you going to do first? 02:19.130 --> 02:23.860 You have seen that we have a trigger in your trigger digital. 02:24.610 --> 02:31.500 What you are going to do to start measuring the distance is you're going to send so the signal will 02:31.510 --> 02:32.580 be low by default. 02:32.940 --> 02:41.880 You are going to send a high signal or 10 microseconds and then look after the ultrasonic sensor will 02:41.880 --> 02:45.060 be triggered and thus will start to measure the distance. 02:45.270 --> 02:48.710 OK, this is an active measurement, not a passive one. 02:49.050 --> 02:56.040 So because this is active, what the ultrasonic sensor will do, it will send burst, OK, with some 02:56.040 --> 02:57.540 wave or some pulse. 02:57.780 --> 03:07.200 It will send it in front of its OK to the range that is in front of it and then it will just wait until 03:07.200 --> 03:09.570 it receives some pulse back. 03:09.670 --> 03:16.530 OK, so if there is an object in front of the sensor, the wave will bounce on the object and will be 03:16.530 --> 03:17.760 returned to the sensor. 03:18.120 --> 03:25.460 OK, so the sensor will measure the duration of how long the wave takes to come back to the sensor. 03:25.860 --> 03:33.110 And then once it has measured this, then you will get some data on the echo pin. 03:33.270 --> 03:40.770 OK, so you have the training and equipping so the equipment will be low by default and then the ultrasonic 03:40.770 --> 03:44.730 sensor will simply but this thing. 03:44.740 --> 03:46.800 So you will read this as an input. 03:47.040 --> 03:53.130 It will put this being high for a certain duration and then low and these duration will be proportional 03:53.130 --> 03:55.050 to the distance of the object. 03:55.260 --> 04:02.190 OK, so if the waves from the sensor comes back very quickly, then the time is quite quick and this 04:02.190 --> 04:04.140 pulse would be quite quick. 04:04.170 --> 04:13.740 Also, if the object is very far at the maximum distance, then these bursts will be longer and the 04:13.740 --> 04:19.710 exact computation for how to measure the distance from the duration here we are going to see that in 04:19.710 --> 04:20.090 the code. 04:20.730 --> 04:21.810 So to quickly, a record. 04:22.440 --> 04:25.920 As a practical recap, you only need to do two things. 04:25.920 --> 04:33.690 First, to send a 10 microsecond high signal on the trigger pin that we are going to do with data. 04:33.690 --> 04:34.020 Right. 04:34.650 --> 04:41.720 And then so this you just need to know it exists, but then you need to simply monitor the echo pin, 04:41.760 --> 04:49.020 OK, and measure the duration of that puts so that ECOFIN will be digital being set as input. 04:49.320 --> 04:52.110 But then how can we measure the duration of that. 04:52.110 --> 04:56.670 But this we are going to use the pulse in function. 04:57.070 --> 04:59.430 OK, and I'm just going to describe quickly. 04:59.690 --> 05:07.940 How does the policing function works so here, this signal here is that one, OK, so it is low and 05:07.940 --> 05:09.740 then it is high and then it is low. 05:10.040 --> 05:11.130 This is a pulse. 05:11.560 --> 05:15.760 Now, what do we want to do is to measure the duration of the outputs. 05:15.830 --> 05:17.570 OK, how do we do that? 05:17.780 --> 05:23.390 Because, well, with digital radio we can know if the signal is low or high, but then how do we measure 05:23.810 --> 05:26.660 the exact duration for the pulse? 05:26.990 --> 05:29.750 Well, we're going to use then the pulse in function. 05:30.110 --> 05:37.310 So when you call the pulse and function the four steps, first one, so you call it, it will start 05:37.550 --> 05:39.160 and then it will wait. 05:39.470 --> 05:42.590 OK, as long as the signal is low, it will wait. 05:42.750 --> 05:50.540 OK, then when the signal rises, so when the signal goes from low to high, the function we start to 05:50.540 --> 05:52.840 measure the duration. 05:53.300 --> 06:00.890 And when the signal goes back to low, the pulse in function will then be able to measure that direction 06:01.130 --> 06:05.510 and it will react in the pulse duration in microseconds. 06:05.780 --> 06:11.720 So you just need to use pulse in function and you can see how it works basically here and you will get 06:11.720 --> 06:14.510 the duration of the pulse. 06:14.880 --> 06:21.380 Also note that this is the high mode, which means that the signal will be first low and then you are 06:21.380 --> 06:25.690 going to measure the bones that is high, but you can also have the opposite. 06:25.710 --> 06:32.480 OK, imagine that the signal is always high and then the pulse is simply the signal going low like this 06:33.110 --> 06:34.790 and then going higher again. 06:35.120 --> 06:40.850 Then you can measure the pulse also with pulse in, but not with the high mode, but with the low mode. 06:41.360 --> 06:46.410 But of course here, because the sensor works like this, we're going to use the high mode.