Experts teach you how to make an LED light-emitting stylus

Publisher:lidong4069Latest update time:2013-11-21 Source: OFweek电子工程网Keywords:DIY Reading articles on mobile phones Scan QR code
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 The main function of a handheld computer stylus is to input handwriting and "point" on the touch screen of the handheld computer. After using it for a few days and researching the original stylus for my handheld computer, I think a suitable stylus should have the following characteristics:

  1. The pen tip should be as small as an ordinary pen, and the pen tip should be hard enough so that it can write smoothly on the small screen of the handheld computer without affecting the user's viewing of the screen content.

  2. The pen tip should be smooth so as not to scratch the delicate handwriting screen. You should know that the handwriting screen is just a layer of plastic film, which is not very hard and strong. It is easy to be scratched by hard objects and leave scratches that are difficult to remove. Too many scratches will eventually seriously affect the clarity of the screen. Moreover, most manufacturers do not provide touch screen replacement services; even if they do, the price is very scary - no less than one-third of the price of the whole machine.

  3. The pen should fit your hand. The input of PDA, especially Chinese character input, basically relies on this small pen. How would it feel if writing on PDA can be as smooth as using pen and paper? Moreover, for most of the friends, they have to use the stylus for a long time every day. Having a stylus that fits your hand can greatly improve the efficiency of using PDA.

  From the above characteristics, we can see that the key to a stylus is the pen tip, which is the part of the stylus that directly contacts the handheld computer. If we can find a suitable pen tip and then directly install the pen tip on the ordinary pen we are used to, we will get a stylus that meets the above three conditions. Of course, since we are doing it, we hope to add some new functions, otherwise I just need to wrap the original stylus with tape, although it looks a bit ugly.

  Although I couldn't think of any suitable new functions for the time being, I still gave up the idea of ​​wrapping tape. It's not that I'm a perfectionist, but for a careless person like me, I will throw away the stylus wrapped with tape within a day, so wouldn't I have no use for the unsuitable one? I'll pay attention to finding materials first.

  First I found a pen that I felt would fit my hand. I usually use a ballpoint pen, and because I have big hands, I feel that a thicker pen is more useful.

  Then I had to find the most critical part - the pen tip substitute. After many days and many places of hard searching, I finally found it, it is - LED! What? Light Emitting Diode? Are you kidding me? Yes! That's it, it can also emit light, cool, right?! The general LED is divided into two specifications: ? 5 mm and ? 3 mm (LED stands for light emitting diode. According to its shape, it is divided into square and round. The round one is divided into 3mm and 5mm according to its diameter, that is, ? 5 mm and ? 3 mm. I used a special-shaped one, so I gave the specific model.), of course, they are too big to be used as pen tips. I used the red high-brightness LED numbered 123ID and the green high-brightness LED numbered 203GD10-001 produced by Taiwan Jiaguang. It should be easy to buy in the local electronic equipment market, only 50 cents.

 

  Light Emitting Diode

  Light Emitting Diode

 

  The small head in the front is only one millimeter in diameter and is particularly smooth. It is made of epoxy resin, which has sufficient hardness and smoothness and is easy to fix. You can fix it directly on the tip of the pen. Leave a lead and connect it to a power source to make it glow!

  Now that we have chosen the pen and the pen tip, let's take a look at how to DIY this cool luminous stylus step by step. First, we need to prepare the other materials needed, including switches, batteries, wires and super glue (an organic adhesive); we also need some production tools such as utility knives, tweezers and electric soldering irons.

 

  1. Study the structure of the pen

 

  Because we need to place batteries, switches and other components in this pen, we need to analyze the structure of the pen first to determine how to place these components. Do you remember the time when you were bored in elementary school and took apart all the detachable pens in your pencil case? Now use your talent and take it apart!

 

  The pen after decomposition

  The pen after decomposition

 

  Among them, the pen barrel is definitely used to install the bulky power supply. From an economic point of view, I choose two No. 7 batteries as the power supply. If the pen barrel you choose is shorter and a little thin, you can also choose a suitable button battery as the power supply. According to my actual measurement, when the light-emitting diode is connected to a 3V power supply, the working current reaches 70mA (without a current limiting resistor). Considering that the brightness of our luminous stylus requires illuminating part of the LCD screen of the handheld computer at night, in order to improve the brightness of the light-emitting diode, we use a connection method that does not connect a current limiting resistor and directly connects it to a 3V power supply. In this case, the light-emitting time of a small button battery is only 30-60 minutes, while the time of a No. 7 alkaline battery is as long as 7-10 hours; the pen tip must be equipped with a light-emitting diode; and the pen cap is just right for installing a switch. In fact, the pen key and the pen core can also come in handy. We will introduce them step by step.   2. Making the pen cap: fixing the switch position and the battery negative pole contact spring

 

  We decided to fix the switch on the pen cap, which is both beautiful and practical. The switch I chose is an ultra-small self-locking push button switch, which has a cross-sectional size of only 7mm X 7mm, just fixed on my pen cap. First, solder the leads of the switch.

 

  First, solder the leads of the switch.

  First, solder the leads of the switch.

 

  The switch also has a beautiful black keycap, which can be seen in the following Figure 11. How to fix it on the pen cap? In fact, it is very easy. You can use something called Super Glue, which is actually epoxy resin glue. The glue contains two kinds of colloidal liquids. When using it, the two colloidal liquids should be mixed evenly in a ratio of 1:1. The contact surface of the objects to be bonded should be coated with the mixed colloidal liquid. After fixing the relative position of the two bonded objects, let it stand for 24 hours. When using this glue, the ratio of the two colloidal liquids must be mastered to be 1:1, and they must be mixed evenly. Otherwise, the glue will be too brittle after solidification or will not solidify for a long time (I have fallen many times here, I hope you don’t learn from me). We will use this glue many times in the following production, including fixing the light-emitting diode on the pen tip. This fixation requires a better bonding effect, otherwise the pen tip will easily tilt or even fall off. So you should read its instructions carefully. After mixing the Super Glue according to the proportion (a little bit is enough, about one drop of each glue), put the switch with the lead soldered in the pen cap, leaving the key part of the switch, and use a toothpick to carefully apply the glue between the switch and the pen cap. Be careful not to get the glue on the key part of the switch, which will cause the key to stick and the switch to fail. After the glue fills the gap between the switch and the pen cap, you can leave it alone for 24 hours.

  Find a battery box for experiment, remove the contact rivet of the positive battery and the spring of the negative battery for later use. Use a utility knife to cut off a part of the pen core (about 3 mm) facing inward, and use a soldering iron to make two small round holes facing each other on the end of the pen core in the direction of cutting. Pass the switch lead fixed on the pen cap through the pen core, and then pass the two leads through the two small round holes on the pen core. Weld one of the leads with the spare spring just now, and then fix it on the pen core. I tried two ways to fix it, one is to use "super glue"; the other is to straighten the tail end of the spring, heat it with a soldering iron, and insert it into the pen core to fix it. Both methods are OK. The other lead passes through the front half of the pen barrel (the pen tip shown in Figure 3) and meets the LED. Finally, we get the finished pen cap.

 

  Finished pen cap

  Finished pen cap

 

  3. Making the pen tip - fixing the positive contact point of the battery and the light-emitting diode

 

  Solder a lead to the rivet removed from the battery box in the previous step. Use a utility knife to cut off the protruding teeth around the pen key as shown in Figure 3. Use a soldering iron to heat the rivet and fix it to the middle of the pen key.

 

  Use a soldering iron to heat the rivet and fix it in the middle of the pen key

  Use a soldering iron to heat the rivet and fix it in the middle of the pen key

 

  The bottom of the LED used as the pen tip is still relatively large, so we need to process the pen tip, mainly by using a utility knife to cut off a little bit of the pen tip, so that the size of the pen tip is basically the same as the bottom size of the LED used as the pen tip, so that it is easier and more firmly to bond the LED of the pen tip to the pen tip of an ordinary pen. Because the glue we use is completely transparent, it will not affect our luminous pen tip. As for whether to bond a red LED or a green LED, you can choose at will. I personally think that the green effect is better, mainly because the green light feels brighter than the red light in the dark, and the general Palm uses a green backlight panel.

  Pass the leads of our pen cap through the pen body and the leads of the pen keys through the pen tip together, where the leads of the pen cap are welded to the negative pole of the light-emitting diode, and the leads of the pen keys are welded to the positive pole of the light-emitting diode.

 

  The lead wire of the pen cap passes through the pen barrel and the lead wire of the pen key passes through the pen tip together

  The lead wire of the pen cap passes through the pen barrel and the lead wire of the pen key passes through the pen tip together

 

  

  The whole pen

 

  Use Super Glue to glue the pen keys and LED to the pen tip, and we have basically completed the main work  of the luminous stylus .

 

  After completing the previous step, we can proceed to the final assembly of the luminous stylus. First, carefully rotate the pen cap onto the pen barrel, and insert two No. 7 batteries from the pen tip direction, with the pen cap direction as the negative pole. Then rotate the pen tip onto the pen barrel, and put the switch keycap onto the switch, and we are done.

 

  

  The final light-emitting stylus

 

  When I press the switch on the top of the pen in a dark environment, there is no eerie green light. How scary! The following picture shows the light pen and my HC-2000 in a dark night (because it is completely dark and my digital camera can't take a picture, I used a little light, but there is no light in actual use.), from the picture we can clearly see the brightness of the pen tip.

 

  Brightness of the pen tip

  Brightness of the pen tip

 

  In my actual use, I feel that the pen is a bit heavy because of the battery, which may not be suitable for some weak friends. I suggest these friends to remove the battery when using it normally, and install the battery in the dark at night. After I assembled this luminous pen, one of my friends (palm owner) knew about it and insisted that I give him one. I asked why. It turned out that the backlight of the palm handheld computer only illuminates the screen area, not the writing area. It is difficult to input at night or when the light is dim. Some people disassemble the machine and replace it with a transparent handwriting area film, and then add a backlight circuit behind the handwriting area, which is too difficult. A luminous stylus completely solves this problem. So I borrowed his palm V and took Figure 13 in the same dark night. We can clearly see the text in the handwriting area. Later, according to my information, palm V has a built-in lithium battery. We can redesign a luminous stylus that uses the battery of the handheld computer itself. The pen body can be smaller and the shape can be more flexible, but it just needs to have a small braid. I am currently experimenting with this, and if the results are good I will write them down for everyone to share.

Keywords:DIY Reference address:Experts teach you how to make an LED light-emitting stylus

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