Created on: 10 March 2023
How to build an electronic flashlight kit or electronic torch kit for beginners in electronics. This tutorial shows how to solder an electronic flashlight kit. In addition it shows how to assemble the kit in a plastic enclosure. An electronic flashlight kit is also known as an electronic torch kit.
The electronic flashlight kit used in this tutorial has the markings EQKIT, 18122F-Y76-200214, FLA-1, and 161007 on the circuit board, or printed circuit board (PCB) as shown in the following image.
Various product codes and descriptions are used for the same kit, depending on where it is sold. For example, the kit may be sold under the product ID 1167834, and description: EQKIT DIY FLA-1 Simple Flashlight Circuit Board Electronic Kit. On another website the kit description is: Simple Flashlight DIY Kit Module for Soldering Electronics Practice. Another example description is: FLA-1 1.5V Simple Flashlight DIY Kit Integrated Circuit Board Soldering Practice Suite Electronic Components Welding Training.
The electronic flashlight kit or torch kit consists of a printed circuit board (PCB), electronic components, and a plastic enclosure. The only additional item needed to operate the kit once built is a single 1.5V AAA cell or AAA battery. A 1.2V AAA rechargeable cell or battery also works.
All of the parts from the electronic flashlight kit are shown in the following image.
The table below lists the parts from the above image.
|1||Plastic Enclosure||Plastic enclosure that is cut out to fit the finished PCB and battery. Cut-outs are on either end of the enclosure for the switch and LED.||Enclosure|
|1||Flashlight Circuit Board||Flashlight printed circuit board.||PCB|
|1||YX8115||LED driver IC or integrated circuit in a TO-92 package.||Integrated Circuits|
|4||47Ω||47 ohm resistor. Value and number of resistors may vary per kit. Only one 47Ω resistor is used to build the flashlight. Others are for soldering practice.||Resistors|
|1||Switch and Button||A switch with separate plastic button that clips to the top of the switch.||Switches|
|2||Spring Terminals||One positive and one negative spring terminal that form the battery holder when soldered to the PCB.||Battery Spring Terminals|
|1||8mm White LED||White LED (Light Emitting Diode) that produces the light from the flashlight or torch.||LEDs|
|1||47µH||47µH inductor or coil.||Inductors|
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The idea of this kit is to learn soldering and then have a useful product after building the kit – that is, a miniature flashlight. Some extra resistors are provided in the kit that can be soldered to a practice area on the circuit board for beginners to practice soldering. Afterwards, solder the kit to build the flashlight or torch.
Use a soldering iron, solder wire and a helping hands magnifier to build the kit, as well as a pair of side-cutters, and small long-nose pliers. A helping hands magnifier or similar clamping tool is essential for this project in order to solder the battery spring terminals to the board.
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Step-by-step instructions on how to assemble the electronic flashlight kit follows below on this tutorial page. The following image shows the completed kit, fully assembled, but with the top of the enclosure removed.
Ordinarily a 1.5V cell can not light up an LED, as the voltage is too low. The components in the flashlight circuit boost the voltage to a higher value. As a result, the circuit is able to switch the LED on.
Before soldering the electronic flashlight kit, beginners can solder some of the spare resistors to the Practice part of the circuit board.
Follow the instructions below for soldering the resistor to the board, but solder a resistor to the practice area instead if you are new to soldering. The practice area is marked 'Practice' on the circuit board and consists of an array of evenly spaced holes, as the previous image shows.
A general rule when soldering an electronic kit is to solder the lowest profile components to the board first. If taller components are soldered first, then it can be difficult to fit the lower profile components to the board afterwards.
In this electronic flashlight kit, the resistor is the lowest profile component, so it is soldered first. Before soldering the resistor, it must be properly identified. Some kits come with four 47 ohm resistors, while others may come with two 47 ohm resistors and two resistors of a different value. Be sure to have one 47 ohm resistor left over after practicing to use in the actual flashlight circuit.
The value of a resistor is read from the colored bands on the resistor. A 47 ohm or 47Ω 5% tolerance resistor has the color bands Yellow – Violet – Black – Gold as shown in the resistor color chart. Yellow has the value 4, violet has the value 7 and black has the value 0. Gold shows that the resistor has a 5% tolerance, which means that the actual value of the resistor is between 47 ohms plus 5% and 47 ohms minus 5% for a 47 ohm resistor.
On a 5% tolerance resistor, the first band represents the first number of the resistor value. Similarly, the second band represents the second number of the resistor value. The third band, however, represents the number of zeros in the resistor value. This means that a 47 ohm resistor's color bands that have the value 470 when looked up on the resistor color chart consists of 4, 7 and no zeros. This means that the value is 47 ohms and not 470 ohms.
The following image shows the 47 ohm resistors from the kit. There are four resistors joined by paper tape. However, only one of these resistors is needed in the torch circuit. The other resistors can be used for soldering practice on the Practice area of the circuit board.
Before heating up the soldering iron, make sure that it is in a safe place, for example in a soldering iron stand. This is to ensure that it does not burn anything when it gets hot. Only pick up the soldering iron by its handle. Never touch the shaft or tip as they will burn you when hot.
To solder a resistor to the circuit board, first plug the soldering iron into a wall socket and switch it on. This allows the soldering iron to heat up. Take the sponge out of the soldering iron stand and wet it under a tap. Squeeze out the excess water and then place it back in the soldering iron stand. The damp sponge is for cleaning the soldering iron tip.
An explanation of how to solder a resistor to a circuit board below is followed by a video that shows the steps.
Resistors are usually attached to paper tape, as the previous image shows. Cut a resistor from the paper tape using side-cutters. Cut through the lead or leg of the resistor near the paper tape on each end of the resistor.
Bend both leads of the resistor down so that the leads can be pushed through the holes in the circuit board. Either insert the resistor into the Practice area of the circuit board, or if building the final circuit, insert the resistor into the place marked R1 on the top of the circuit board.
Push the resistor all the way down so that the leads pass through the holes in the board and the resistor body lies flat on the board. Bend the resistor legs or leads out slightly so that it does not fall out of the board.
Turn the board over and place it on a flat surface that is suitable for soldering on. Afterwards, solder one lead or leg of the resistor at a time. It may help to wipe the soldering iron tip on the damp sponge. Melt some solder wire on the tip of the iron to see that it is hot enough. Wipe the tip on the sponge again to clean the tip.
To solder, touch the tip of the iron on the circuit board pad to be soldered so that it also touches the lead of the resistor being soldered. Feed some solder wire into the area where the pad, resistor leg and soldering iron meet. The solder should melt and form a nice joint. Don't leave the soldering iron tip on the joint for too long, 3 to 5 seconds is usually enough. Heating up a component too much may damage it.
Once the solder joint has formed, remove the solder wire and the soldering iron. Clean the soldering iron tip on the sponge and solder the second resistor lead. Allow the solder joint to cool for a few seconds.
After both joints are soldered, cut the excess length of the resistor leads or legs off using side-cutters.
If you are not confident about soldering yet, first see the article on soldering irons and the article on soldering for beginners before proceeding. In fact, be sure to read the article on soldering for beginners as it contains additional safety tips. In addition, watch the video below.
This video shows the above steps performed.
After practicing soldering, and after soldering the resistor, proceed to solder the remaining components to the board as follows.
The cylinder shaped inductor must lie flat on the circuit board, but the legs of the inductor protrude from the end of the cylinder shape. This means that the leads of the inductor must be bent down 90 degrees each before soldering. Use a small pair of long-nose or similar pliers to bend the leads, as shown in the following video. Afterwards, insert the leads into the board at the shape marked L1 and 47µH. Bend the leads out slightly to prevent the inductor dropping out of the board.
Use a 'helping hands' magnifier to hold the board while soldering. Turn the board over and solder the two leads as shown in the video. Finally cut the excess length of the legs of the inductor off on the bottom of the circuit board as the video shows.
The TO-92 package that the YX8115 IC is housed in has a flat surface and curved back. This shape is found marked on the top of the circuit board. In addition, the shape is marked U1.
Insert the leads or legs of the YX8115 into the three holes where marked on the board. Make sure that this part is oriented the correct way around. Check that the flat surface of the part matches up with the flat marking on the board. Likewise with the curved surface.
Clamp the board upside down in the helping hands clip. Solder each pin on the board. Finally clip the excess length of the legs from the component using side-cutters. The following video shows all of the steps to solder the YX8115.
Push the button cap onto the top of the switch. The switch is a component that must lie on its side, but has legs or leads protruding from the bottom. As with the inductor, the switch leads must be bent 90 degrees before soldering.
Use small long-nose or similar pliers to bend the leads 90 degrees as the following video shows. Afterwards, insert the three bent pins of the switch into the holes at the shape marked S1 at the end of the circuit board. Finally clamp the boards in the helping hands clip and solder as the video shows. It may be necessary to solder one pin, then hold the board in a hand and push down on the switch. Then melt the solder joint to make sure that the switch is positioned and soldered flat on the board. After this, solder the other pins as the following video shows.
The LED must lie on its side, so the pins or leads of the LED must be bent 90 degrees. Before bending the pins, it is important to note that the LED has one longer lead and one shorter lead. The correct LED lead must be inserted into the correct hole of the electronic flashlight kit circuit board. This means that it matters which way the leads are bent. If the wrong lead is soldered into the wrong hole, then the flashlight won't work. See the beginner's article on LEDs for the LED symbol and polarity.
Another important thing to note before soldering the LED is that the main body or bulb of the LED does not fit through the hole in the plastic enclosure. Only the top of the LED slightly protrudes through the hole. This means that most of the body of the LED is inside the enclosure. In addition it means that the leads must be bent at 90 degrees where they enter the body of the LED.
Bend the LED pins or legs 90 degrees down so that, when looking at the bottom of the LED with the bent pins pointing down, the longer lead is at the left. The following image shows the correct position of the LED with the long lead at the bottom of the image. In this position the leads are bent 90 degrees down, into the image as it were, for the correct LED polarity when inserted into the circuit board.
After bending the LED pins 90 degrees at the body of the LED, check again that the long lead is at the left when looking at the bottom of the LED where the pins come out, with the pins pointing down.
Insert the LED pins into the holes near the end of the circuit board in the shape marked D1. An image of the assembled kit from the top of this page is included again below for reference. The long lead of the LED is at the bottom of this image, although does not appear to be long with the LED fitted and leads cut.
With the LED in the correct position, solder the leads of the LED in the circuit board. Once again, it is helpful to first solder one pin. Afterwards, push the LED flat onto the circuit board and heat the solder joint again so that the LED is put in the correct position on the board, as it may have shifted when soldering the first joint. Finally, solder the other pin or lead of the LED. Cut the excess length of the LED leads off when finished. Test fit the circuit board in the plastic enclosure when done.
The following video shows how to bend the LED pins and solder the LED to the electronic flashlight kit.
A helping hands magnifier, or similar clamping tool, is essential when soldering the battery spring terminals to the electronic flashlight kit board. This is because each spring must be held in place flat on the board. Never hold the spring by hand when doing this soldering job, as the spring heats up quickly and will burn fingers.
The image below shows where the battery spring terminals are placed. With the electronic flashlight kit circuit board positioned with the LED at the left, the taller spring is placed at the left. This is the negative battery spring terminal. Place the flat spring at the right of the board, near the on/off switch. This is the positive battery terminal.
To solder the battery spring terminals, start with the flat positive battery spring terminal. Clamp it in one of the helping hands magnifier jaws. Place the circuit board in the other jaw. Adjust the jaws so that the pin of the spring terminal is placed in the correct position on the bottom of the circuit board. That is, the pin lies flat across the four pads marked with a plus (+) sign. Solder the pin to the board, as shown in the following video. Run the solder and iron down the pin so it covers all four pads.
After soldering the positive terminal, do the same for the negative terminal. Make sure that the spring of this terminal points inwards and not to the outside of the end of the board. Solder the pin of this spring terminal to the four pads marked negative (-) on the board. See the following video for details.
Finally we look at how to assemble an electronic flashlight kit. This is the easiest step in building the flashlight, as it consists of fitting the circuit board into the plastic enclosure and inserting the AAA cell or battery. Assuming that the LED and switch were soldered in the correct positions on the circuit board, the board should easily fit into the plastic enclosure.
Place the completed electronic flashlight kit circuit board into the deeper half of the plastic enclosure. Insert a 1.5V AAA cell into the enclosure. Do this by pushing the negative end of the cell against the tall spring near the LED. Finally push the 1.5V cell down so that the positive terminal makes contact with the flat spring at the switch end of the flashlight.
Push the top half of the plastic enclosure onto the bottom half. The kit is now complete. Push the on/off switch at the end of the enclosure to switch the flashlight on and off. The following video shows how to assemble and test the electronic flashlight kit. A 1.2V rechargeable AAA cell is used in the video.