Electronics: Lesson 013 - Experiment 14: Wearable pulsed luminaries

experiment 14： Wearable pulse illuminant

up to now , I have been encouraging you to connect various devices together , But there are not many theories or plans .“ Discover learning methods ” this is it , There are plans to take you step by step to achieve your goals .

Items needed

• Connecting line 、 Wire nippers 、 Wire stripper 、 A multimeter 、15W Soldering iron 、 Auxiliary tool
• 9 V Batteries and connectors , or 9 V communication — DC adapter
• Fine wire （0.6mm）
• Ordinary perforated plate
• resistor ：470 Ω 2 individual 、100 kΩ 1 individual 、4.7 kΩ 2 individual 、470 kΩ 2 individual
• Capacitor ：3.3 μF 2 individual 、220 μF 1 individual
• 2N2222 The transistor 3 individual
• Universal LED 1 individual

Review oscillations

Please turn back to the picture 2-116, Recall the memory of this circuit . Now? , Your task is to make it as small as possible , So you can wear it on your body .

chart 3-66 It shows one of my most successful attempts to reduce the circuit size , The circuit is built in one piece 0.9×1.3 Inch ordinary perforated plate . Here are some ways .

• Use rated power 1/8 W A small resistor , Instead of 1/4 W The resistor .
• Install the resistor vertically .
• If the hole in the perforated plate is large enough , Put two leads through the same hole .

Where are the connecting wires between components ？ Under the board . In the figure 3-67 in , I painted the components grey , The board is omitted , So you can see the wiring method .

If you compare this circuit diagram with figure very carefully 2-116 Compare the circuit diagrams in , You'll find that , The connection mode between components is exactly the same

chart 3-68 Shows another view , This time the components are omitted , Only the circuit board is displayed , In this way, you can see how the connecting wire fits on the circuit board 0.1×0.1 Inch mesh .

Last , chart 3-69 Shows the circuit board flipped to the right , So you can see the back of it . This diagram will help you connect circuit components . You will try , Right ？

Bend the pins and weld

So how should you make all the connections ？

It's not difficult . resistor 、 The pins of capacitors and transistors are usually at least... Long 1/2 Inch . therefore , You can insert them into the holes in the perforated plate , Then bend the pins , Make them touch each other , And then weld them together . Cut off the extra pins , Connect the battery , The work is done .

You need to pay attention to three main issues .

• It requires a certain amount of caution and patience to keep the circuit board stable during operation . It is necessary to use auxiliary tools .
• The distance between the component and the weld will be very close , Please use copper spring clip to provide heat dissipation protection .
• It is troublesome to turn the circuit board over and over , It's easy for you to connect the wires in the wrong position . I think this is the most difficult part .

Perhaps you have seen such a perforated plate ： A ring of copper is added around each hole . Is such a porous plate suitable for this experiment ？ The advantage of the copper ring is that it can firmly fix the components , But they can also create short circuits between wires that are very close . I think bare circuit board is easier for such a small project . chart 3-22 An example is shown . Some perforated plates have larger holes , But there is not much difference .

Step by step

The following are the specific steps to build the circuit .
Cut an ordinary perforated plate , The size is 0.9×1.3 Inch .（ There is no need to use a graduated ruler , Just count the rows of holes on the board .）

Get all the components ready , Carefully insert threeorfour elements into the holes , Count the number of holes , Make sure that the components are positioned correctly .

Turn the board over , Bend the pins of the components , Fix them on the board , Make it as shown in the figure 3-69 Connection shown . If any pins
Not long enough , You have to use a paragraph 22 Wire gauge to supplement . Remove the insulation from the conductor , Because the insulation layer has a blocking effect .

Roughly trim the wire with wire cutters .

Weld with a soldering iron .
Now is the most important part ： Inspect each weld with a close-up magnifying glass , Twist the wire with pointed nose pliers . If there is not enough solder , Cannot form a solid weld , Just reheat , Add a little more solder . If the solder forms the wrong connection position , You can use the art knife to cut two parallel cuts on the solder , Scrape off the middle part .

Usually , I only weld threeorfour components at a time , Because if there are too many , I get confused easily . If I solder a component in the wrong position , It is not too difficult to correct mistakes —— Unless I have welded more components when I find the error .

Be careful ： Flying wire segment

The jaws of the thread cutting pliers are very powerful , When cutting wires , Power will reach its peak , Then suddenly release . This force will be transformed into the kinetic energy of the cut wire segment . Some wires are soft , No threat , But transistors and LED The pins of are hard , There may be danger . A small piece of wire will fly out at a high speed at an unpredictable angle , When you are working closely , Very dangerous to eyes .

Ordinary glasses can protect your eyes when trimming wires . If you don't wear glasses , Using plastic goggles is also a very good way .

Finish the work

I usually use bright lights . This is not luxury , But necessary . If you don't have a lamp , Just buy one . Desk lamps don't have to be expensive , The cheaper one is OK .

I use the sunlight spectrum LED Desk lamp , Because it can help me identify the color band on the resistor more reliably . I used to use a fluorescent lamp , When I found that any small flaw in the coating of the lamp tube would let the ultraviolet light leak out , I won't use it anymore . When working under the lamp at close range , Ultraviolet radiation poses a threat .

No matter how good your eyesight is , You should use a magnifying glass to inspect each weld . You will be impressed by the imperfection of some welds . Put the magnifying glass as close to your eyes as possible , Then pick up the circuit board , Slowly approach the magnifying glass , Until the weld you observe becomes clear .

Last , The circuit you make should send out pulses like a heartbeat . Is it right? ？ If the circuit does not work , Please go back and check each connection point , Compare it with the circuit diagram . If no problems are found , Just add power to the circuit , Connect the black probe of the multimeter to the negative pole , Check the voltage at each point of the circuit with a red probe . When the circuit is working , Each part should have at least a certain voltage . If you find that the voltage at some connection point is zero , It may be because the weld joint is broken , Or no welding at all .

After finishing the circuit , What should we do ？ Now you can change from an electronics enthusiast to a craft enthusiast . You can try to think of a way , Make the circuit wearable .

The first thing to consider is the power supply . Due to the requirements of the components used , Circuit needs 9 V The power supply can work normally . How to carry a huge 9 V In the case of batteries, this circuit can be transformed into wearable devices ？

I think of three ways .

• You can put the battery in your pocket , Install the flash device outside the pocket , A thin wire goes through the pocket .
• The battery can be installed inside the top of the baseball cap , The flashing device is mounted on the front .
• You can put three sections 3 V Button batteries are stacked together , Put it in a plastic clip , But I'm not sure how long they will last .

I must explain , In this experiment 2N2222 Transistors are not ideal , Because they use more power than field effect transistors （ also
It's called MOSFET） more . however , I decided to use only one class of transistors in this book , And bipolar NPN T-type transistor is the most basic type .

Say it again LED The choice of . Transparent LED Will produce a well-defined beam , It may not be suitable for this experiment , And the diffuse beam is more attractive . In order to spread LED Beam of light , You can take LED Installed in a piece with a thickness of at least 1/4 Inch clear acrylic plastic
in , Pictured 3-70 Shown . Grind the surface of acrylic plastic with fine sandpaper , It is best to use a rotary sander , It doesn't grind out obvious patterns . such , Acrylic plastic becomes translucent .

Drill a hole in the back of the acrylic plastic LED Slightly larger hole , But don't drill through . Blow some compressed air into the hole , Remove debris and dust from the hole . If you don't have an air compressor , Washing with water is also OK .

After the borehole is completely dry , Use some transparent silicone or mix some transparent epoxy , Drop by drop at the bottom of the hole .

And then put LED Push into the hole , Fill with epoxy LED Around , Form a tight seal .

Lighten up LED, If necessary , Continue sanding acrylic plastic . Last , You can decide to install the circuit on the back of acrylic plastic , Or lead out a wire to connect to another place .
You can choose the resistance of the resistor in the oscillator circuit , send LED The flickering frequency of is close to that of the heart when the human body is still .

So the whole device looks like it's measuring your pulse , If you place the device in the center of your chest or strap it around your wrist , That's more like . If you like pranks , You can claim that your health is simply too good , Even when you do strenuous exercise , The pulse can be kept constant .

In order to make a beautiful shell for the device , I considered several options , From mounting the whole device in transparent epoxy resin to looking for Victorian style small boxes , wait . Leave the other options to yourself , Because this is an electronics textbook , Instead of handicraft teaching materials . however , I would also like to explain a problem related to handicrafts , Now is a good opportunity .

Background knowledge ： Crazy metrics

In this book , I mainly use inches as the unit of measurement , But sometimes I risk using metric units of measurement , for example “5 mm
LED”. It's not because I didn't achieve unity , This reflects the current situation of contradictions in the electronic industry ： Inches and millimeters are commonly used in daily life , It often appears on the same data sheet . for example , The pin spacing of surface mount chips is usually expressed in mm , However, the pin spacing of the through-hole chip is still expressed as 0.1 Inch , And it may keep going .

What makes things more complicated is , Where inches are used , There are two different ways to express fractional inches . for example , The size of the drill bit is
1/64 Multiples of inches indicate . The metal gasket is made of 1/1000 Multiples of inches （0.001 Inch 、0.002 Inch , wait ） rank . What's more puzzling is , The thickness of a sheet metal is usually measured in “ Wire gauge ” Express , for example 16 The thickness of wire gauge steel sheet is about 1/16 Britain .

Why doesn't the United States use the metric system ？ The metric system seems more reasonable ！

We can discuss its rationality . The public metric system is applied to 1875 When it was formally proposed in ,“ rice ” Is defined as following a line through Paris , The distance from the north pole to the equator 1/10 000 000. Why Paris ？ Because this concept was put forward by the French . after that , After a series of efforts to improve the accuracy of scientific applications ,“ rice ” It has been redefined three times .

Speaking of the practicality of the decimal system , Moving a decimal point is certainly better than calculating an inch 1/64 It's simpler , But the only reason we use the decimal system is that we happen to be used to counting with ten fingers . The dodecal system is really more convenient , Because numbers can be 2 and 3 to be divisible by .

All the above are conjectures . The fact is that , We can't get rid of the contradiction of length measurement , So I drew four tables , Help you with the conversion between systems . You can see from the table that , If necessary for 5 mm Of LED Drill a hole ,3/16 Inch drill bit is suitable .（ actually , This kongbi is really 5 mm The drilled hole is smaller .）

chart 3-71 Will help you in 1/64 Inches and 1/100 Conversion between multiples of inches . The gray column is divided into 64 Share , The blue column is divided into 32 Share , The green column is divided into 16 Share , The orange column is divided into 8 Share . Usually , If a value can be expressed exactly in larger units , We use this representation ; So we don't say an inch 8/64, And say an inch 1/8. When you try to compare the two measurements, which is the greater , This representation can cause confusion —— for example ,11/32 Inch ratio 5/8 Inches big ？

Please check the chart to confirm your guess .

Because datasheets often use decimal decimals in inches to represent dimensions , So figure 3-72 The second table in has decimal and 64 Conversion between bases . You're likely to see 0.375 Measurements like inches , Know that it is equal to 3/8 Inch , Class knowledge is very useful .

Many data sheets provide both millimeter and inch measurements , But some data are expressed in millimeters only . If you're still used to thinking in inches , Or want to know if the element is suitable for bread board or perforated board 1/10 Inch hole spacing , Then remember 1/10 Inches equals 2.54 mm Will be very useful . If the element is very small , that 2.5 mm Multiple pin spacing is acceptable . however , Not less than 25 mm The pin spacing of may not adapt to the spacing of 25.4 mm（ That is, one inch or more ） The hole of .

chart 3-73 Mm is shown 、1/100 Multiples of inches and 1/64 Conversion relationship between multiples of inches .

chart 3-74 The picture is 3-73 Enlarged edition , It shows 0.1 mm Multiple of and 1/1000 Conversion relationship between multiples of inches .

For the past 40 years , The United States has made some progress in adopting the metric measurement system , But it will take decades for the conversion to be completed . in the meantime , Anyone using parts or tools manufactured or sold in the United States should be familiar with these two measurement systems , There is no other way .