Lightning Detector Design Competition
閃電探測器設計比賽

Introduction
概論

The goal of this workshop is to show the principle of lightning detection and to introduce a simple circuit for detection of strong electromagnetic signals or light flashes, which are produced by electric sparks, lightning included. The reader should note that while the principle applies to lightning detection in general, the circuit introduced is by no means the only circuit for lightning detection.

When there is lightning, strong but transient electromagnetic waves are produced. On an oscilloscope, the waveform looks like that shown in Figure 1, where the current induced by an electric arc generated by a manual electric arc lighter is shown. Note the time scale on the horizontal axis of the graph. The electromagnetic disturbance only last for a few milliseconds, and so even if we can capture the disturbance, we need to convert it into some longer-lasting signal so it can be seen by an observer far from the detector.

在這工作坊，我們會解釋探測閃電方法的原理，並介紹一個電路，能探測電弧放電或閃電所產生的強力電磁波或閃光。 讀者須注意，雖然此工作坊所介紹的原理能在不同範疇使用，但電路則有不同變化，所介紹的只是其中一例。

閃電會產生強力但短暫的電磁波，波形類似圖一。 該圖顯示了電感一手動電弧放電點火器所產生的電流。 請注意橫軸時間軸的尺度，波形顯示電磁波只有數毫秒。 故此，我們需將訊號延長，以便遠離探測器的觀察員觀察。

The reader is also reminded that real lightning often consists of multiple electric arc discharges happening at different times during different stages of lightning. Interested parties can refer to books such as [1] for more information.

So, a lightning detector needs to do two things:

1. Capture the electromagnetic disturbance
2. Convert the millisecond-long signal to a longer signal for display or recording

In the following sections, we will introduce how these can be done in the lab setting. Since the capturing circuit has more variations, let's introduce the conversion circuit first.

實際上，在一組閃電的不同階段，有多於一次的電弧放電。想了解更多，請參考書籍，如[1]。

因此，一個閃電探測器需要做兩件事：

1. 捕捉閃電所引致的電磁波干擾，
2. 將以毫秒計的訊號轉換成一個長訊號，以便顯示或記錄。

以下幾節，我們會介紹如何在實驗室做到以上兩點。因為捕捉電磁波干擾有多種方法，我們先介紹將訊號轉換的方法。

From a flash to a second — the monostable
將一瞬變成一秒 — 單穩態電路

A circuit that converts a short pulse to a longer one is called a monostable circuit. It is called "monostable" because it only has one stable state, which, in our case, signals non-detection of the pulse. A monostable circuit can be triggered into the other state by an input pulse. In our case, it is the pulse from a detected electric arc.

There are many ways a monostable circuit can be constructed. One relatively simple way is to use the timer integrated circuit (IC) NE555. The IC is shown in Figure 2, and the circuit is shown in Figure 3. In this circuit, a when the input to pin 2 of NE555 has a voltage higher than 2/3 of the supply voltage V_s, the output at pin 3 of NE555 will go high (i.e., near to supply voltage) for a while, determined by the resistor R_t and capacitor C_t. The formula for the time that the output will go high is t ≈ 1.1 R_t C_t.

輸入一個短脈衝，輸出狀態會改變一段時間的電路，叫做單穩態電路。 顧名思義，單穩態電路只有一個穩定的狀態。 在我們的應用來說，代表了沒有閃電。 當有脈衝輸入，電路就會離開穩定狀態一會兒，那就代表了偵測到有電弧放電。

製作單穩態電路有很多方法。 想對容易的，就是用一個名為NE555的集成電路(IC)。 圖二為該集成電路的外觀，圖三則為單穩態電路的電路圖。 當NE555的第二腳的電壓高於其供電電壓V_s之2/3時，第三腳輸出就會變高一陣子，時間取決於電阻R_t和電容C_t，公式為時間 t ≈ 1.1 R_t C_t.

Capturing the flash
抓住那一瞬

With the monostable circuit in place, what we need to do next is to generate the pulse that triggers it when lightning is detected. We can do it in a number of ways, some of which are listed as follows:

1. Use an inductor to pick up electromagnetic disturbances (Figure 4)
2. Construct a electronic inductor—capacitor resonator similar to that in AM radio, and tune it to a frequency of a few hundred kilohertz (Figure 5)
3. Construct a fast-reacting light sensor circuit that detects changes in light intensity (Figure 6)

We are going to give brief explanation of these circuits.

有了單穩態電路，下一步要做的，就是在有閃電時產生觸發電路的脈衝。這有很多方法，以下是其中幾種：

1. 利用電感器感應電磁波干擾（圖四）
2. 如調幅(AM)收音機般，利用電感電容諧振器調至數百千赫的範圍。（圖五）
3. 利用高速光電感應器偵測光度的轉變（圖六）

以下，我們會簡單地介紹這幾個電路。

Inductor-based electromagnetic disturbance detector
利用電感器感應電磁波干擾

The idea for the design of this electromagnetic disturbance detector is very simple: electromagnetic waves caused by lightning or electric arc are able to induce currents in an inductor. These current can be AC-coupled (alternating current-coupled), to trigger the monostable. In this circuit, a coil is used as an inductor. A capacitor is used to block direct currents, and couple only the induced current to the monostable.

Note that since the induced current can flow in both ways along the inductor, the induced current spike have both a positive and a negative part. Also, the current spike can be very large in amplitude. To avoid damage to the monostable circuit, sufficient protection should be in place. For example, a current limiter circuit can be used to limit the amplitude of the current spike.

電感器感應電磁波干擾基於一個簡單的原理：閃電或電弧放電的電磁波會在電感器裏產生感應電流。 這電流可以利用交流電耦合去觸發單穩態電路。 在這電路中，一個線圈可以用作電感器。 電容則用來阻擋直流電，以作交流電耦合。

要注意的是，電感器會感應到正方向的電流，亦會感應到反方向的電流。 同時，瞬間電流值可以很大。 要單穩態電路免受傷害，要有適當的保護。 例如限流器可限制電流的幅度。

Tuned resonator
諧振器調諧

An inductor stores energy as magnetic field, and a capacitor stores energy as electric field. Because there is a 180˚ phase difference between these forms of energy storage, coupling an inductor and a capacitor together forms the basis of an electronic resonator. Given an inductor with inductance L and a capacitor with capacitance C, the resonant frequency f is 1/(2π√L̅C̅).

A lightning generates signal in many frequency bands, but it would be convenient to tune the LC resonator to the carrier frequency of an AM radio, from about 400kHz to 1000kHz.

Since only a particular frequency is picked up by the LC resonator, the signal would be relatively weak when compared with the one picked up by just an inductor. However, since the spectral characteristics of lightning varies across type and stage of lighting, tuned resonators are often used in advanced lightning detection and analysis systems. To use this kind of resonator effectively, some kind of amplification of the resonator output is often needed.

電感器利用磁場儲存能量，而電容器則利用電場來儲存能量。 因為它們儲存能量的方法有180˚的相位差，電感器耦合電容器可以造出一個諧振器。 若電感器的電感量為L,電容器的電容值為C,諧振器的諧振頻率 f 為 1/(2π√L̅C̅).

閃電會產生很多不同頻率的訊號。 我們可以很方便地將電感電容諧振器的頻率調至調幅(AM)收音機的頻率，即400kHz至1000kHz.

因為電感電容諧振器只取其諧振頻率的訊號，訊號強度很多時會比只用電感器感測弱。 然而，因為不同閃電不同階段的諧波頻率不同，不少較專業的系統會用類似的方法分析閃電。 要有效地使用諧振器來分析閃電，通常需要放大階振器的輸出。

Detect light intensity changes
偵測光度的轉變

To detect sudden changes in light intensity, we can use some fast-responding components such as the light sensing elements used in a web camera, or a photo diode. Since a web camera is designed to interface with a computer and the processing of its image has been covered in a previous workshop, here we focus on the use of a photo diode.

A photo diode, like a normal diode, allows current to flow in one direction only. Yet, different from a normal diode, the amount of current flow is controlled by light intensity that falls upon the photo diode. More currents can flow when the incident light intensity is high, Hence, a simple current-limiting circuit is enough to capture light intensity.

To capture the change of light intensity, a capacitor is used to block the direct current (DC) part of the signal. In general, quick changes of light intensity would cause sudden change of voltage on the diode end of the capacitor, which generates a voltage spike on the load end.

要偵測光度的突然轉變，我們可以用些對光度轉變反應快的元件，例如網絡攝影機的感光元件，或是光敏二極管。 因為網絡攝影機主要設計來與電腦連接，而上個工作坊己討論和示範如何用網絡攝影機分析其所頡取的畫面，這次我們主要討論光敏二極管。

光敏二極管如普通的二極管，只容許電流單向流動。 和普通的二極管不同，光敏二極管容許的電流量取決於落於那光敏二極管的光照量。 光照量大，容許的電流量會高。 因此，簡單的限流電路就可以用來感光。

要偵測光度的轉變，可用電容器來阻擋光度訊號的直流部分。 光度的轉變越快，光敏二極管那邊的急速的電壓轉變耦合到電容器，產生電壓尖峰。

Lab work
工作坊實驗

This section guides you through the lab work for the construction of a simple electric arc detector.

在本節，我們會帶大家製作一個簡單的電弧探測器。

Understanding the circuit diagram and components
認識電路圖和電子零件

Our first step is to construct the monostable circuit whose schematic diagram is shown on Figure 3. Afterwards, a detector will be constructed to trigger the monostable circuit. Before we start constructing the monostable circuit, let's take some time to understand the diagram and the components needed to construct the circuit.

All upward pointing arrows in the circuit diagram connect to the positive side of the power supply, and all symbols with three lines going downwards forming a triangle are grounded to the negative side of the power supply.

The largest piece of component on the circuit diagram, is a rectangle that corresponds to the IC NE555, and the numbers are the pin numbers of the IC. In the workshop, the IC used is in Dual In-line Package (DIP), and looks like that in Figure 2. Note that there is a notch on the DIP IC. If we put the notch at the top, we can number the pins from 1 on by counting counterclockwise from the top left hand corner, as shown in Figure 7.

首先，我們會造一個單穩態電路，電路圖如圖三。 然後，我們會造一個用以觸發它的電弧探測器。 在製造單穩態電路前，讓我們先了解電路圖中的符號，與及它們所代表的電子零件的樣子。

在電路圖中，所有向上的箭咀代表連接電源的正極，而所有有越來越短三橫劃的，都代表要「接地」，即是電源的負極。

電路圖中題大的方塊，代表集成電路(IC) NE555,而方塊裏面的號碼，就是它的引腳編號。 本工作坊所用的，是雙列直插封裝(DIP)的集成電路，樣子如圖二。 留意該IC有個凹位，用來判別引腳編號。 當凹位向上，其右上角的腳是第一腳，逆時針數便是第二腳，如此類推，如圖七。

In the circuit diagram, the zig-zag symbol correspond to resistors. Resistors limit current flow and its values are measures in ohms, with the greek letter Ω as symbol. The larger the value the resistor, the smaller will be the current flow given the same voltage. With a resistor value of R and a voltage of V, the current I=V/R. This can be remembered as V=IR.

Resistors look like those in Figure 8, and are nonpolar. That is, unlike batteries, installing a resistor one way of another does not matter. Resistor values are colour-coded, and the table for the code for commonly-used resistors can be found in Figure 9. The resistance is read as follows. First, identify the tolerance band. If there is a gold or silver band at the end of the resistor, it must be the tolerance band. Otherwise, probably your resistor has five colour bands, and a brown band at one end, which could be a bit separated from other bands or very much near the end of the resistor, is the tolerance band. The colour band besides the tolerance band is the multiplier band. Other colour bands are value bands.

From the opposite side of the tolerance band, start reading the value bands. This would form a two- or three-digit number. The value of the resistor is the number, multiplied by the multiplier indicated by the multiplier band, in ohms. Two examples are shown in Figure 10.

電路圖上鋸齒形的符號代表電阻。 電阻減低電流，單位為「歐姆」Ohm,利用希臘字母Ω代表。 電阻值越大，施加同樣電壓時電流越小。 若電壓為V,電阻值為R,電流I就等於V/R。 此公式亦可以V=IR記之。

電阻的外觀如圖八，是無極性元件。 即是說，不像電池，正反來安裝也沒所謂。 電阻值利用色碼表示，圖九為常用電阻色碼表。 要知一電阻的阻值，首先要確定哪個是誤差色環。 如其一尾端之色環是金色或銀色，那肯定是誤差色環。 如沒有，那電阻很可能是有五個色環，而其中一尾環會是啡色的誤差色環。 它通常會距離其他色環較遠，或該環較近尾部。 誤差色環旁的，就是倍數色環。 其他的，就是代表數值的色環。

要讀電阻值，先由不是誤差色環的那面開始，讀數值色環的數值。 這會得出一個兩位或三位數。 將此數乘以倍數色環所代表的值，便會得出電阻值，單位為歐姆。 圖十為兩個例子。

The component whose sign has two parallel lines are capacitors. Capacitors store energy in form of electric field across its adjacent but insulated plates. The amount of charge q stored in a capacitor whose plates are applied a voltage V is related to the capacitor's capacitance C by the formula q=CV. Capacitance has the unit of Farads. Practical capacitors usually have capacitance in the range from a few picofarads pF, or 10^-12F, to a few thousand microfarads µF, that is 10^-6F.

In the workshop, two kinds of capacitors are used. Monolithic capacitors, or mono caps (Figure 11), are used for capacitors with smaller capacitance. Mono caps are nonpolar. Its capacitance can be read from the markings on the capacitor. Usually, there are three numbers, and the capcaitance is the first two numbers, added with as many 0s as specified in the third number (i.e., multiply by 10 raised to the power of the third number), in pF. For example, a capacitor marked "274" has a capacitance of 27 x 10⁴ pF = 270000 pF = 270nF = 0.27µF. What are the capacitances of the capacitors in Figure 11?

In a circuit diagram, nonpolar capacitors are usually marked without anything in the middle of the two parallel lines.

Another kind of capacitors used is called electrolytic capacitor. They got their names because electrolytes are used in constructing them. Electrolytic capacitor are polarized, that is, they have positive (+) and a negative (-) connections which cannot be reversed. Their capacitance are usually larger, from a few µF to thousands of µF. Because of their larger physical size, their capacitances are usually marked directly on the component. The polarity of the leads are also marked, usually by marking the negative terminal with a band of - signs, though some of them would mark only the positive terminal or both.

In a circuit diagram, polarized capacitors such as electrolytic capactiros are usually marked with slanted lines in the middle of the two parallel lines. The polarity are also marked, typically by marking the + terminal, though sometimes both + and - terminals are marked. Also, the lead for the + terminal of a new capacitor are usually longer than that for the - terminal. Yet, the marking on the component should be treated as definitive.

電路圖中，有兩條平行線的符號代表電容器。 電容器可以儲存能量於它兩片相鄰但絕緣的導體的電場中。 如電容兩端的電荷為q,兩端電壓為V,而電容量為C,則q=CV. 電容量的單位為「法拉」Farad,或簡為「法」，利用英文字母F代表。 常用的電容值由數皮法picofarads pF (10^-12F)至數千微法microfarads µF (10^-6F).

在此工作坊，我們會用兩種電容器。 電容值較小的，我們會用積層陶瓷電容器mono cap（圖十一）。 Mono cap 無極性，其電容值可從其表面的數字解讀。 通常，mono cap 的表面有一組三個數字。 電容值為首兩個數字，後加第三個數字那麼多個零（即乘以十的第三個數字那麼多的次方），單位為pF. 舉例來說，一個標示"274"的電容，其值為 27 x 10⁴ pF = 270000 pF = 270nF = 0.27µF. 圖十一那幾個電容的電容值是多少？

在電路圖中，無極性的電容器的符號中，兩線中間留空。

我們在工作坊會用的另一款電容，為電解電容器。 顧名思義，電解電容器內有電解質。 電解電容器有極性，有正極(+)和負極(-)，安裝時不能調轉。 它們通常有較大的電容量，幾微法µF至幾千微法都有。 因為它們體積較大，它們的容量通常都直接印在元件上。 它們的極性亦會有標示，如以一條有負號的帶來表示負極，亦有只標示正極或正負皆標。

電路圖中，有極性的電容器如電解電容的符號的兩平行線中用斜線表示，並以+號表示正極，又或+極-極皆表。 新的電解電容，正極引腳通常長些，但辨認極性，我們應以元件上的標示為準。

Now the only unexplained component in the circuit diagram has the symbol of a big triangle pointing to a thick line, with two small arrows near it. It is the light emitting diode, or LED. Like ICs, LEDs are semiconductor components. LED is a special kind of diode, which is a component that allows one-way flow of current only. What makes LED different from a normal diode is that when there is current flow, it lights up. Thus, they are ideal in being indicators voltage levels. Usually, a resistor is needed to limit the current flow through an LED so it would not be burnt.

Since an LED allows unidirectional current flow only, it is polarized. The direction of current flow is along the triangle in the circuit diagram. The side current enters is marked as positive (+), and the other side negative (-). Similar to capacitors, the lead on the positive side of a new LED is often longer.

You can also determine the polarity by looking at the transparent or translucent LED itself (Figure 13). Inside an LED, one side is larger in size than the other. The larger side connects to the negative (-) terminal. For other types of diodes including the Zener diode (Figure 14), the negative terminal is marked by a bar on the component package.

現在，唯一一個未介紹的元件的符號，是一個指向一條粗線的大三角。 它代表發光二極管。 像集成電路，發光二極管是半導體元件。 發光二極管是一種特別的二極管。 在二極管內，電流只能單向流動。 發光二極管特別的是，電流通過時，它會發光。 故此，它們可用作顯示電流有沒有通過。 通常，發光二極管要用電阻以限流，以免被燒壞。

正因發光二極管只能讓電流單向流動，它是有極性的元件。 電流由符號中三角形那邊的正極流往粗線那邊的負極。 一如電容器，新的發光二極管正極腳會長些。

其實，我們可以從透明或半透明的發光二極管的結構，得知其引線的極性（圖十三）。 發光二極管中，金屬大些的那邊為負極。 至於其他種類的二極管，包括圖十四中的然納二極管，負極引線那邊有一粗線以作標記。

Now that we understand the schematic diagram of the circuit and can identify the components, it's time to construct the monostable circuit.

現在明白了如何閱讀電路圖和辨認電子元件，是時間製造單穩態電路了。

Constructing the monostable circuit
製作單穩態電路

One easy way of constructing a circuit temporarily for experiment is to use a breadboard. A breadboard is a board with internal connections and holes for placing components. Usually, there are connected holes on the two sides for power supply connections (black for ground, red for positive voltage), and those in the middle are connected every row, though rows and rows are not connected. Figure 15 shows the breadboard used in the workshop and Figure 16 shows its internal connections.

To use the breadboard to construct the circuit, some planning is needed to make sure the circuit connections are equivalent to that shown in the circuit schematic. Figure 17 shows our plan. Jumper wires are used to connect some of the middle bars to the power supply bars as required in the circuit schematic, and the two power supply bars on the two sides have to be connected as well. Note that an extra capacitor is added to the lower right hand side of our plan which is used to smooth the voltage supplied to the IC when it changes state. The value of this capacitor does not matter much as long as it is reasonably large; 47µF or 100µF should be good enough. The choice of values for R_t and C_t and the calculation of the time constant are also shown in the plan.

The power is supplied by the battery case with a power switch, shown in Figure 18. The red wire correspond to the positive power supply, and the black wire the ground. With four AA batteries, the supply voltage would be 4 x 1.5V = 6V.

Before connecting the battery case and testing the circuit, check very carefully that the connections on the breadboard, the orientation of the IC, and polarity of the LED and capacitors are correct. After checking, switch off the power on the battery case, and connect it to the circuit. Make sure the polarity of the power supply connections are correct. Wrong connections may burn out the IC or cause fire if the battery is short circuited.

Since the circuit is small, if you follow the breadboard plan, the monostable circuit takes up only a few rows of space on the breadboard, as shown in Figure 19.

製作小型的電子電路，其中一種簡易的方法就是用麵包版。 麵包版上有孔洞以安插電子電件，而內部有電氣椄各洞。 通常，麵包版兩邊的洞用來作電源（紅正黑負），電中間的洞就每行相椄，但行與行之間並不相連。 圖十五為工作坊所用的麵包版，而 圖十六顯示其內裏的連接圖。

利用麵包版砌電路，我們需要計劃如何安放零件。 圖十七是這個單穩態電路安放零件的草圖。 我們會利用跳線連接電源往一些在中間的排洞，與及將兩邊的電源排連接起來。 要留意我們在右下角加了一個電容，以作當IC轉變其輸出時，平穩電壓之用。 只要數值足夠大，這電容用甚麼數值不太重要。 47µF 或 100µF 也可以。 圖中我們也顯示了 R_t 和 C_t 的選擇和計算。

我們用圖十八的有開關制的電池盒來供應電源。 紅線是電源正極，黑線為負極地線。 電源用四顆1.5V電池，故電源電壓為 4 x 1.5 = 6V.

接電源及測試電路前，我們須小心核對麵包版上的連線、集成電路的方向、與及發光二極管和電容的極性。 核對後，關上電池盒的電源，將其連接往麵包版。 請肯定電源極性正確，否則小則燒壞IC，大則電池短路，引致火災。

因這是個十分小型的電路，如果跟從草圖安放零件，只會用到麵包版上的幾行，如圖十九。

Testing the monostable circuit
測試單穩態電路

Since a low voltage pulse to the Trigger pin (pin 2) of NE555 monostable circuit would cause it to spring into action, and that its pin 1 is the ground pin, the easiest way to test is to temporarily short circuit pins 1 and 2 of the NE555 using a wire or something metal. Of course, remember to turn on the power before testing. After triggering, the LED should stay on for about 0.3 second, then go off. If the test fails, turn off the power and check the connection and polarity of components one by one.

此單穩態電路只需用一個在NE555第二腳的低電壓觸發。 因為第一腳是電源地線，要測試電路，只需用電線或金屬物將第一二腳短暫短路。 測試前當然要開電源。 電路觸發後，發光二極管會發亮大約0.3秒，然後熄滅。 若測試不成功，便要電源再核對有甚麼弄錯了。

Constructing the electric arc detector
製造電弧探測器

In this workshop, we use inductor detector to trigger the monostable circuit. The simplest inductor detector is just a coil in series with a coupling capacitor, shown earlier in Figure 4. Because a capacitor is used to block DC signals, the output of the inductor detector can be directly used as the trigger input of the monostable circuit.

Theoretically, we can calculate the best capacitance and inductance for optimal detection of electric arc discharges. Yet, because the calculation can be quite complicated, let us experiment a bit. Since capacitance values cannot be changed easily, let us fix it so that C = 0.1µF. On our breadboard, one of the leads of the 0.1µF capacitor should be connected to pin 2 of the NE555 IC, and another lead should be seated on one of the holes whose connection bar does not connect to anything else.

Now let us construct the inductor by making a coil. Wind about 6 to 8 turns of a piece of wire on a water bottle, take the bottle out afterwards, and this is our inductor. When winding, make sure that the ends of the coil are long enough for connecting to the breadboard. Connecting one end of the coil to the capacitor, and the other end to the ground bar, and the circuit is complete. The finished circuit would look like the one in Figure 20.

It's time to test the circuit using a electric arc lighter! Switch on the circuit, and generate electric arc using the electric arc lighter near the coil, and the LED should light up for a while. Figure 21 shows the circuit being tested and the LED lighting up. (The circuit in the photo is slightly different from the one introduced but the difference is inconsequential)

在此工作坊，我們會利用電感器感應電磁波干擾，以觸發單穩態電路。 最簡單的電感探測器，用一個線圈串聯一個電容，如圖四。 因為電容器不容直流電通過，這電路可以用來直接觸發單穩態電路。

理論上，我們可以計算出能檢測電弧放電的最佳的電感量和耦合電容量。 然而，因為此計算可以甚為複雜，我們就來做些實驗吧。 因電容量不易改變，我們先將之定為 C = 0.1µF. 我們可以放一只0.1µF電容在麵包版上，一腳連接NE555的第二腳的洞，另一腳連接一個暫未接其他零件的洞。

現在是製造電感器的時候了。 將六至八圈的電線繞着一個水樽，然後取出水樽，這便是我們的電感器了。 繞線圈時，要多留一點線尾，以便將線圈接往麵包版。 將線圈的一端接往電源地端（負極），另一端接往剛才那電容，那便大功告成。 完成品將如圖二十。

是利用電弧點火槍測試的時間了！ 開電源，然後用火槍在線圈附近製造電弧閃電，電路上的發光二極管會亮着一會。 圖二十一顯示測試中的情況。 （圖中電路與剛才所介紹的有輕微而不重的不同。）

Time to experiment!
實驗時間！

Since the inductor is just a coil that can be wound and unwound easily, it would be interesting to experiment to see the effect of construction of the coil on the sensitivity of the detector circuit. Here are some ways for the interested to explore:

1. Is the electric arc detection directional?
2. How does sensitivity change with the number of turns of the coil?
3. How does sensitivity change with the size of the coil?
4. Would an 8-shaped coil be more sensitive or less?
5. Does the sensitivity change if we put some magnetic materials (e.g., iron) inside the coil?

因為電感器其實是一個易於裝拆的線圈，我們可以做些實驗，看看線圈的結構如何影響電路的靈敏度。 這裏有一些方法，讓有興趣的探索一下：

1. 線圈有方向性嗎？
2. 靈敏度與線圈有多少圈有何關係？
3. 靈敏度與線圈的話大小有何關係？
4. 8字形的線圈會靈敏些還是沒那麼靈敏？
5. 線圈中如有些受磁的東西（如鐵），電路的靈敏度會被影響嗎？

Some points to note
要注意的幾點

Electric arc discharge induces current that flow in both directions in the inductor. When coupled to the monostable, the large induced current may cause a high voltage that would damage the IC. Hence, practically, we should protect the input of the monostable from seeing high voltages. One way is to put a Zener diode with a voltage rating similar to the supply voltage from the ground to the input pin of the iC. The disadvantage is that this would desensitizes the detector. Though with the disadvantage, protection circuit should be in place for out-of-lab use.

電弧放電會使電感器感應到正方向和反方向的電流。 當與單穩態電路耦合後，強大的電感電流引致的高壓可能會燒燬IC. 故此，實際使用時，我們須保護單穩態電路的輸入，免受高壓的破壞。 一個簡單的方法，就是加一個與電源電壓值相若的然納二極管，由電源地端往IC的輸入腳。 這方法的壞處，就是會令電路靈敏度減低。 雖然有壞處，如電路要於實驗室外用，必須有保護電路。

While the LC resonator circuit may need components to amplify the signal for coupling to the monostable circuit, similar to the inductor-based electromagnetic disturbance detector, the light intensity change detector introduced in Figure 6 can be coupled directly to the monostable circuit. Figure 22 shows the coupled circuit.

雖然電感電容諧振器可能要一些零件去放大訊號及耦合單穩態電路， 像利用電感器感應電磁波干擾般，圖六所介紹的光度轉變偵測器可以直接耦合單穩態電路。 圖二十二為耦合了的電路。

References
參考資料

1. Lightning: Physics and Effects Vladimir A. Rakov, Martin A. Uman Cambridge University Press March 2007 ISBN:9780521035415
2. NE555 Single Precision Timer Data sheet Texas Instruments SLFS022H 1973—2010
3. NE555 General purpose single bipolar timer Data sheet STMicroelectronics Doc ID 2182 Rev 6 2012