Pratique du Shadowing: Turn a Time-of-Flight Sensor into a 3D Scanner - Apprendre l'anglais à l'oral avec la vidéo
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139 phrases
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Today I want to show you a little setup that I've got here on the breadboard.
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These are all parts from Aliexpress so it's a relatively cheap setup.
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The ESP cost me about £4, the time of flight sensor cost me about £5 and this IMU was about £15.
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So it's the most expensive part of the system and if we wanted we could replace it with a cheaper alternative.
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So this whole setup cost about £24, that would be $30 or €28.
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Eros.
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So the reason why this tiny LiDAR is so special is that it is a multi -zone time -of -flight sensor.
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So what that means is that instead of shooting out a single ray
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and measuring the distance at which that ray bounces off an obstacle, it shoots out a 8x8 grid.
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So those are 64 rays coming out of it that will bounce back once they hit an obstacle.
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Now I've connected the breadboard to my computer via a USB cable and the LED is on so we know it's powered.
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Here in the viewer now we can see that we've got roughly the same layout for the two breakout boards.
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We have the IMU in purple and the time -of -flight sensor in green.
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Here on the right we have the status panel showing the live data
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and we can see that the IMU is connected
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and we're getting measurement data from the time -of -flight at about 15 Hz.
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Now you see these blue rays shooting out from the time -of -flight sensor.
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There are 64 of them arranged in an 8x8 grid and each represents one zone that the sensor can measure.
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Notice how they don't start right at the sensor, there's a small gap.
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And they extend outward, but not infinitely.
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If I zoom out, you can see that.
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These line segments span the sensor's measurable range from 2 cm to 4 m.
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Now, this is fundamentally different from how cameras work.
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A camera captures light across a continuous image, but the sensor, it can only measure along these specific rays.
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The points you see here, they're locked to these line segments.
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They cannot appear anywhere else
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and you can see as I slide my hand across the sensor you see the points going left
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and right and also back and forth
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and I can also hold my hand like this
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and just slide my finger underneath it
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and you can see there's a wave changing the points from the from the palm of my hand
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now here's where it gets interesting let me zoom out
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and we will see the points here that are projected onto the ceiling of the room where I'm at.
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And you see in the settings panel this option here for clipping to measurement.
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Let me enable it and let's see what happens.
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Do you see how the rays now stop at the measure points instead of extending to the maximum range?
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This is a much more accurate representation of what's actually physically happening.
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The sensor shoots out infrared laser pulses.
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They travel along these paths, bounce off of whatever obstacle they hit, and reflect back.
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The sensor measures how long that took, that's the time of flight, and calculates the distance.
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So when I hover my hand over the sensor, you can see some rays clip at my hand while others continue to the ceiling behind it.
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And that's exactly what's happening in the real world.
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Some laser pulses are hitting my hand, others are missing it and hitting the ceiling.
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I think this visualization does a much better job of conveying what this sensor does compared to some 2D heatmaps
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that you typically see online.
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And it's a lot of fun to play with.
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Alright, I've zoomed back in because I want to talk a bit about this purple breakout board here.
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It's an IMU.
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And watch what happens in a visualizer when I rotate the breadboard in the real world.
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It also rotates.
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The IMU on the breadboard is tracking the orientation in real time
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and since both the IMU
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and the time -of -flight sensor are stuck to the same breadboard we always know which direction the sensor is pointing.
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Let me zoom back out and you can kind of see how if I point around I
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can measure different points around my room.
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Let's place the breadboard back on the table you may notice
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that the points are a bit jittery
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and that's just sensor noise from radiation coming from the window or noise from the actual sensor measurement.
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Now if I come over here to the side panel
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and enable that filter you can see how the noise kind of smooths out
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and I can control the strength of the filter with this slider.
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What's happening under the hood is an exponential moving average.
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At 0 .5 strength, each new position is calculated as 50 % of the new measurement plus 50 % of the previous position.
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So it's essentially averaging the current and previous readings.
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If I crank up the strength to 0 .9, it gets even smoother.
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But now there's a noticeable lag.
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So when I move this two -point from the ceiling to the wall, you can see that the points are really smooth,
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but there's a noticeable delay.
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At 90 % previous and only 10 % new measurement, the visualization can't keep up with the fast movements.
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So it's a trade -off between smoothness and responsiveness.
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If I move the strength all the way down to 0, that essentially means there is no filter.
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It's the same as if this checkbox was left unchecked.
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And watch what happens if I move all the way to 1.
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That means that the previous measurement gets all the weight and 0 % is assigned to the new measurement.
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So even though I'm rotating the breadboard around the room, you see that no new measurements are coming in.
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Let me move the slider back to 0 .5, which I found to be a good strength for the filter.
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Alright, let's move on to the next section.
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The viewer can also fit the plane to the measured points.
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When I enable plane fitting with the least squares method and point the sensor at a flat surface like the ceiling,
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you can see if it's a nice plane.
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But watch what happens when I point the sensor at both the wall and the ceiling at the same time.
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The fitted plane ends up diagonally, trying to minimize the error across all points, and this is not very useful.
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This is where RANSAC comes in.
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RANSAC stands for Random Sample Consensus.
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When I switch to this method, watch how it behaves differently.
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RANSAC works by randomly picking three of these sampled points, the minimum to define a plane.
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Fitting a plane to those three, then checking how many other points lie close to that plane,
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and it repeats this about a hundred times and keeps the best fit.
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The key difference is, instead of trying to please all the points equally,
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Ransack finds the plane that the majority of points agree on and ignores the outliers.
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So now when I point again at both the ceiling and the wall, it snaps to whichever surface has more points.
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Rather than compromising with a meaningless diagonal.
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And so even if I come in with a pen to disturb the sensor measurements,
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you can see how it still is able to be robust to that and fit the ceiling nicely.
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And if I change to least squares,
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you see how much the disturbance from waving this pen on top of the sensor affects the fitted plane.
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I'm going to change again to RANSACK now.
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If you cover enough points you can see that it still affects the plane fitting algorithm,
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but most of the time it behaves much better than least squares.
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I've changed to least squares again.
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I'm just hovering the pen back and forth and I'm gonna change to RANSACK again.
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It's a really big difference.
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Up until now we've been showing the current snapshot seen by the sensor.
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In other words, the viewer is only showing the points that the sensor sees right now at any given point in time.
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When new measurements come in, the old points disappear and that's why it is so interactive.
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Mapping mode changes that.
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Instead of replacing points, it accumulates them.
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So watch what happens when I hover my hand over the sensor with mapping mode enabled.
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You can see points starting to build up in the shape of my hand's movement,
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and covering most of the sensors point field of view up close almost like a truncated pyramid.
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Okay I've zoomed back out and cleared them up.
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Here's where the magic really happens.
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You remember we have the IMU tracking orientation right?
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So watch what happens when I rotate the breadboard.
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Look at that!
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The accumulated points are building up a map of the room so I can see the walls, the ceiling, my monitor, my desk,
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if I go under the desk I can see the floor
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and if I point at myself you'll even be able to see me
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and I can even put my left arm up
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and then my right arm up and
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because we're no longer just showing the instantaneous points
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that the sensor is measuring we've just accumulated them we essentially have a map of the room we have a mapping device
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Now, the reason why this works is because the IMU knows exactly
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which direction the sensor is pointing at as I rotate it, and each measurement gets placed in the correct position in 3D space,
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and they all accumulate into a coherent point cloud.
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This is really cool!
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With just an ESP32, a time -of -flight sensor, and an IMU, we've essentially built a simple 3D mapping device.
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Now there's one limitation worth mentioning.
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The IMU is excellent at measuring rotation, but it cannot accurately track translations, moving the sensors side to side or forward and back.
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So if I walk around with a breadboard, the map will drift and become inaccurate.
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For best results, I always try to rotate the sensor in place without translating too much, just like this.
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Within that constraint, you get surprisingly good results from such a simple and cheap setup.
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And that's it!
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This concludes the video.
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I think this demo really shows how powerful the combination of a multi -zone time -of -flight sensor
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and an IMU can be.
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And for around $30 in parts, you can build something that gives you a real intuition for what the sensors are actually measuring
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and could be useful for a robotics project.
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Thanks for watching and I'll see you in the next one!
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale s’appuie sur la vidéo « Turn a Time-of-Flight Sensor into a 3D Scanner ». Les mots qui reviennent le plus souvent : sensor, Imu, measurement, plane, breadboard. Cette vidéo contient 42 phrases et 1785 mots à répéter en shadowing. La partie parlée dure 11:19. Le locuteur parle à un rythme naturel d’environ 158 mots par minute, proche d’une conversation courante. Seuls 78 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots de la vidéo à retenir, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| sensor nom | /ˈsɛn.sɚ/ | détecteur, capteur |
| measurement nom | /ˈmɛʒ.ə.mənt/ | mesure |
| ceiling nom | /ˈsilɪŋ/ | plafond |
| rotate verbe | /ˈɹoʊ.teɪt/ | tourner, rotationner |
| essentially adverbe | /ɪˈsɛnʃəli/ | essentiellement, en essence |
| enable verbe | /ɪˈneɪ.bəl/ | autoriser, permettre |
| filter nom | /ˈfɪltɚ/ | filtre |
| smooth adjectif | /smuːð/ | doux, facile |
| bounce verbe | /baʊns/ | rebondir |
| viewer nom | /ˈvju.ɚ/ | spectateur, spectatrice |
| obstacle nom | /ˈɑbstəkəl/ | obstacle |
| desk nom | /dɛsk/ | bureau, pupitre |
| connect verbe | /kəˈnɛkt/ | accoupler, connecter |
| extend verbe | /ɛkˈstɛnd/ | étendre |
| purple nom | /ˈpɝ.pl̩/ | violet, pourpre |
Les verbes à particule que vous entendrez
| Mot | Prononciation | Sens |
|---|---|---|
| hand over verbe | remettre, donner | |
| zoom out verbe | /ˌzuːm ˈaʊt/ | dézoomer |
| build up verbe | s'accumuler, s'entasser | |
| come over verbe | venir | |
| end up verbe | se terminer, se finir | |
| keep up with verbe | aller de pair avec |
Des phrases à répéter
Des phrases courtes et complètes de la vidéo, à réutiliser dans la conversation de tous les jours :
- Let me enable it and let's see what happens.
- Let's place the breadboard back on the table.
- All right, let's move on to the next section.
- I've changed to least squares again.
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Phrases conditionnelles if + proposition, will/would + verbe — une condition et son résultat | if I point at myself you'll even |
| Present perfect have/has + participe passé — une action passée qui compte encore maintenant | I've connected · I've zoomed · I've changed |
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | is connected · are projected · is calculated |
Prononciation à surveiller
Le locuteur utilise 21 contractions et formes réduites, comme I'm, I've, we've. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « th »: smooth /smuːð/, underneath /ˌʌndɚˈniθ/, algorithm /ˈælɡəɹɪðm̩/
- Les sons « sh » et « zh »: measurement /ˈmɛʒ.ə.mənt/, essentially /ɪˈsɛnʃəli/, orientation /ˌɔː.ɹi.ənˈteɪ.ʃən/, capture /ˈkæp.(t)ʃɚ/, translation /tɹænzˈleɪʃən/
- Mots longs — placez bien l’accent: essentially /ɪˈsɛnʃəli/, orientation /ˌɔː.ɹi.ənˈteɪ.ʃən/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, radiation /ˌɹeɪ.diˈeɪ.ʃən/, differently /ˈdɪf.ə.ɹənt.li/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: behave /bɪˈheɪv/, coherent /koʊˈhɛɹ.ənt/, hover /ˈhɒvə/, hertz /hɝts/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: arrange /əˈɹeɪnd͡ʒ/, whichever /wɪt͡ʃˈɛvɚ/, checkbox /ˈt͡ʃɛkbɑks/, exponential /ˌɛk.spəˈnɛn.t͡ʃəl/, jittery /ˈd͡ʒɪt.ə.ɹi/
- /r/ anglais — langue recourbée, sans frotter la gorge: rotate /ˈɹoʊ.teɪt/, grid /ɡɹɪd/, orientation /ˌɔː.ɹi.ənˈteɪ.ʃən/, reflect /ɹɪˈflɛkt/, translation /tɹænzˈleɪʃən/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme sensor, measurement, ceiling.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.