シャドーイング練習: Turn a Time-of-Flight Sensor into a 3D Scanner - 動画で英語スピーキングを学ぶ

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Today I want to show you a little setup that I've got here on the breadboard.

These are all parts from Aliexpress so it's a relatively cheap setup.

The ESP cost me about £4, the time of flight sensor cost me about £5 and this IMU was about £15.

So it's the most expensive part of the system and if we wanted we could replace it with a cheaper alternative.

So this whole setup cost about £24, that would be $30 or €28.

Eros.

So the reason why this tiny LiDAR is so special is that it is a multi -zone time -of -flight sensor.

So what that means is that instead of shooting out a single ray

and measuring the distance at which that ray bounces off an obstacle, it shoots out a 8x8 grid.

So those are 64 rays coming out of it that will bounce back once they hit an obstacle.

Now I've connected the breadboard to my computer via a USB cable and the LED is on so we know it's powered.

Here in the viewer now we can see that we've got roughly the same layout for the two breakout boards.

We have the IMU in purple and the time -of -flight sensor in green.

Here on the right we have the status panel showing the live data

and we can see that the IMU is connected

and we're getting measurement data from the time -of -flight at about 15 Hz.

Now you see these blue rays shooting out from the time -of -flight sensor.

There are 64 of them arranged in an 8x8 grid and each represents one zone that the sensor can measure.

Notice how they don't start right at the sensor, there's a small gap.

And they extend outward, but not infinitely.

If I zoom out, you can see that.

These line segments span the sensor's measurable range from 2 cm to 4 m.

Now, this is fundamentally different from how cameras work.

A camera captures light across a continuous image, but the sensor, it can only measure along these specific rays.

The points you see here, they're locked to these line segments.

They cannot appear anywhere else

and you can see as I slide my hand across the sensor you see the points going left

and right and also back and forth

and I can also hold my hand like this

and just slide my finger underneath it

and you can see there's a wave changing the points from the from the palm of my hand

now here's where it gets interesting let me zoom out

and we will see the points here that are projected onto the ceiling of the room where I'm at.

And you see in the settings panel this option here for clipping to measurement.

Let me enable it and let's see what happens.

Do you see how the rays now stop at the measure points instead of extending to the maximum range?

This is a much more accurate representation of what's actually physically happening.

The sensor shoots out infrared laser pulses.

They travel along these paths, bounce off of whatever obstacle they hit, and reflect back.

The sensor measures how long that took, that's the time of flight, and calculates the distance.

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.

And that's exactly what's happening in the real world.

Some laser pulses are hitting my hand, others are missing it and hitting the ceiling.

I think this visualization does a much better job of conveying what this sensor does compared to some 2D heatmaps

that you typically see online.

And it's a lot of fun to play with.

Alright, I've zoomed back in because I want to talk a bit about this purple breakout board here.

It's an IMU.

And watch what happens in a visualizer when I rotate the breadboard in the real world.

It also rotates.

The IMU on the breadboard is tracking the orientation in real time

and since both the IMU

and the time -of -flight sensor are stuck to the same breadboard we always know which direction the sensor is pointing.

Let me zoom back out and you can kind of see how if I point around I

can measure different points around my room.

Let's place the breadboard back on the table you may notice

that the points are a bit jittery

and that's just sensor noise from radiation coming from the window or noise from the actual sensor measurement.

Now if I come over here to the side panel

and enable that filter you can see how the noise kind of smooths out

and I can control the strength of the filter with this slider.

What's happening under the hood is an exponential moving average.

At 0 .5 strength, each new position is calculated as 50 % of the new measurement plus 50 % of the previous position.

So it's essentially averaging the current and previous readings.

If I crank up the strength to 0 .9, it gets even smoother.

But now there's a noticeable lag.

So when I move this two -point from the ceiling to the wall, you can see that the points are really smooth,

but there's a noticeable delay.

At 90 % previous and only 10 % new measurement, the visualization can't keep up with the fast movements.

So it's a trade -off between smoothness and responsiveness.

If I move the strength all the way down to 0, that essentially means there is no filter.

It's the same as if this checkbox was left unchecked.

And watch what happens if I move all the way to 1.

That means that the previous measurement gets all the weight and 0 % is assigned to the new measurement.

So even though I'm rotating the breadboard around the room, you see that no new measurements are coming in.

Let me move the slider back to 0 .5, which I found to be a good strength for the filter.

Alright, let's move on to the next section.

The viewer can also fit the plane to the measured points.

When I enable plane fitting with the least squares method and point the sensor at a flat surface like the ceiling,

you can see if it's a nice plane.

But watch what happens when I point the sensor at both the wall and the ceiling at the same time.

The fitted plane ends up diagonally, trying to minimize the error across all points, and this is not very useful.

This is where RANSAC comes in.

RANSAC stands for Random Sample Consensus.

When I switch to this method, watch how it behaves differently.

RANSAC works by randomly picking three of these sampled points, the minimum to define a plane.

Fitting a plane to those three, then checking how many other points lie close to that plane,

and it repeats this about a hundred times and keeps the best fit.

The key difference is, instead of trying to please all the points equally,

Ransack finds the plane that the majority of points agree on and ignores the outliers.

So now when I point again at both the ceiling and the wall, it snaps to whichever surface has more points.

Rather than compromising with a meaningless diagonal.

And so even if I come in with a pen to disturb the sensor measurements,

you can see how it still is able to be robust to that and fit the ceiling nicely.

And if I change to least squares,

you see how much the disturbance from waving this pen on top of the sensor affects the fitted plane.

I'm going to change again to RANSACK now.

If you cover enough points you can see that it still affects the plane fitting algorithm,

but most of the time it behaves much better than least squares.

100

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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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「Turn a Time-of-Flight Sensor into a 3D Scanner」を教材にしています。繰り返し出てくる語は次のとおりです：sensor, Imu, measurement, plane, breadboard。この動画には、シャドーイング用の文が42文、単語が1785語あります。音声の長さは11:19です。話す速さは1分あたり約158語で、日常会話に近い自然なペースです。英語の頻出3,000語に含まれる単語は78%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
sensor 名詞	/ˈsɛn.sɚ/	センサー, センサ
measurement 名詞	/ˈmɛʒ.ə.mənt/	測定
ceiling 名詞	/ˈsilɪŋ/	天井
rotate 動詞	/ˈɹoʊ.teɪt/	回る
zoom 動詞	/zuːm/	猛スピードで進む
filter 名詞	/ˈfɪltɚ/	濾過器, フィルター
smooth 形容詞	/smuːð/	スムース
viewer 名詞	/ˈvju.ɚ/	視聴者
obstacle 名詞	/ˈɑbstəkəl/	障害, 邪魔
desk 名詞	/dɛsk/	机
connect 動詞	/kəˈnɛkt/	繋げる
purple 名詞	/ˈpɝ.pl̩/	紫
slide 名詞	/ˈslaɪ̯d/	滑り台
segment 名詞	/ˈsɛɡmɛnt/	切片
laser 名詞	/ˈleɪzɚ/	レーザー

動画に出てくる句動詞

単語	発音	意味
hand over 動詞		引き渡す, 手渡す
zoom out 動詞	/ˌzuːm ˈaʊt/	ズームアウトする, 縮小する
come over 動詞		遣って来る

繰り返し練習したい文

動画に出てくる短く完結した文です。日常会話でそのまま使えます。

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.

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
条件文 if + 節, will/would + 動詞 — 条件とその結果	if I point at myself you'll even
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	I've connected · I've zoomed · I've changed
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	is connected · are projected · is calculated

注意したい発音

話し手はI'm, I've, we'veなど、短縮形や弱形を21回使っています。聞こえたとおりの短い形で発音しましょう。

「th」の音: smooth /smuːð/, underneath /ˌʌndɚˈniθ/, algorithm /ˈælɡəɹɪðm̩/
「sh」と「zh」の音: measurement /ˈmɛʒ.ə.mənt/, essentially /ɪˈsɛnʃəli/, orientation /ˌɔː.ɹi.ənˈteɪ.ʃən/, capture /ˈkæp.(t)ʃɚ/, translation /tɹænzˈleɪʃən/
長い単語（アクセントの位置に注意）: essentially /ɪˈsɛnʃəli/, orientation /ˌɔː.ɹi.ənˈteɪ.ʃən/, representation /ˌɹɛp.ɹə.zɛnˈteɪ.ʃən/, radiation /ˌɹeɪ.diˈeɪ.ʃən/, differently /ˈdɪf.ə.ɹənt.li/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: reflect /ɹɪˈflɛkt/, translation /tɹænzˈleɪʃən/, roughly /ˈɹʌf.li/, differently /ˈdɪf.ə.ɹənt.li/, surprisingly /səˈpɹaɪzɪŋli/
/v/ — /b/ にならないように、上の歯を下唇に当てる: viewer /ˈvju.ɚ/, behave /bɪˈheɪv/, interactive /ˌɪn.tɚˈæk.tɪv/, convey /kənˈveɪ/, whichever /wɪt͡ʃˈɛvɚ/
/f/ — 「フ」ではなく、上の歯と下唇で出す: filter /ˈfɪltɚ/, finger /ˈfɪŋɡɚ/, reflect /ɹɪˈflɛkt/, roughly /ˈɹʌf.li/, physically /ˈfɪz.ɪ.kli/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。sensor, measurement, ceilingなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: Turn a Time-of-Flight Sensor into a 3D Scanner - 動画で英語スピーキングを学ぶ

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