LED luminous stylus DIY

The main function of the stylus pen on a PDA is to input handwriting and "point" on the touch screen of the PDA. The general LED is divided into two specifications: 5 mm and 3 mm. Of course, they are too big to be used as pen tips. I use the red high-brightness LED numbered 123ID and the green high-brightness LED numbered 203GD10-001 produced by Taiwan Jiaguang. They should be easy to buy in the local electronic equipment market, only 50 cents.

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 wire 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 still 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 them apart!

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 pen core can also come in handy. We will introduce them step by step.

2. Production of pen cap: fixed switch position and 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.

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 in 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 switch button part, 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 switch button part, which will cause the button 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 spare 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 fixing methods, 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

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

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 the pen cap through the pen body and the leads of the pen keys through the pen tip, where the leads of the pen cap are welded to the negative pole of the LED, and the leads of the pen keys are welded to the positive pole of the LED.

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

By gluing the pen keys and LEDs to the pen tip with Super Glue, we have basically completed the main work of the luminous stylus.

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