How to make a flashlight from a used battery?

Flashlight from an old battery

Do not throw away your used batteries, because they can still serve. The new alkaline battery has a voltage of 1.5 volts, which decreases as it is used. Eventually, the voltage becomes too small for most devices to work. However, the remaining 15% of the charge can be “pulled out” of the battery with a special device called “Joule thief.” This is enough to light a white LED flashlight, which we will try to make.

The “joule thief” scheme raises the battery’s depleted voltage, but does this in the form of fast pulses. As a result, we will see a constant glow, although in fact the LED will quickly turn on and off.

So, what we need:

Required Tools

  • soldering iron;
  • tool for stripping wires;
  • scissors;
  • Double-sided tape.

Necessary materials

  • battery holder with contacts;
  • 10 mm super bright white LED;
  • a piece of wire from an old network cable;
  • core toroidal transformer (2 cm);
  • button;
  • 1 kΩ resistor;
  • round prototyping board (diameter 2-3 cm);
  • transistor 2N2222 NPN or similar;
  • used alkaline battery AAA, AA, C or D type.

We proceed to build a flashlight:

1. Prepare the battery holder

Step 1

Our battery holder model has a negative (with spring contact and black wire) and positive (red wire) contacts. Route the wires through the holes in the housing so that they come out, as shown in the picture. Note how the negative wire passes from the spring contact.

2. Attach the button

Step 2

Take a double-sided adhesive tape and attach the button to the battery holder from the negative contact side.

3. Solder the button

Step 3

We cut the negative wire of the battery holder near the button, we clean the ends of the wires and solder them to the contacts of the button.

4. Insert the LED

Step 4

Take the circuit board and insert the LED in its center so that its legs pass through the board.

5. Bend and solder the LED feet

Step 5

Bend the ends of the LED, as shown in the figure, and solder them to the adapter holes of the board.

6. Install the transistor

Step 6

Look at the packaging of the transistor or find on the Internet which legs of the element correspond to the emitter, the base and the collector. Install and solder it to the prototyping board above the LED so that the emitter of the transistor is connected to the end of the LED bent upward, and the collector – with the end curved sideways (see figure).

7. Install the resistor

Step 7

Install the resistor on the board directly under the LED. Connect one end of the resistor to the base of the transistor, and bend the second and pull it aside.

8. Prepare the battery holder wires

Step 8

Shorten the wires coming from the battery holder, so that they stick out 3-4 cm from the housing. Then clean and tin their ends.

9. Attach the development board to the battery holder

Step 9

Skip the wires from the previous step through the prototyping board, as shown in the figure. Note that the plus wire must go to the right side of the LED, and the negative wire to the left.

10. Solder the battery holder wires

Step 10

Bend and solder the black wire to the leg of the LED, bent sideways (see photo).

11. Insert the wires

Step 11

Cut two 50-centimeter wires, peel and tin them on one side. Connect the wires to the breadboard. One – to the red wire from the battery (passing through the transfer hole). The second – to the collector of the transistor.

12. Solder the wires of the toroid

Step 12

Solder the wires from the previous step. They will be needed to hold the core of the toroidal transformer.

13. Pass the wires through the core

Step 13

Thread the free ends of the wire through the core. Attach the core to the prototyping board so that the LED and other components are inside it.

14. Wind the core with wires

Step 14

Use the wire coming from the collector of the transistor to “sew” the toroid to the prototyping board. To do this, pass the wire through the vias until you complete the complete circle.

15. Wind the core with a second wire

Step 15

Repeat the previous step for the remaining wire coming from the positive battery positive terminal. Place the wires so that they do not crisscross.

16. Thread the wires from the toroid through the board

Step 16

The ends of the wires with which we wound the core pass through the free holes of the prototyping board, as shown in the photo.

17. Solder the wires of the toroid

Step 17

Solder the first wire to the red wire coming from the battery holder, and the second to the resistor.

18. Check the circuit

Step 18

Check the circuit by inserting the battery into the holder and pressing the button.

19. Attach the card to the battery holder

Step 19

After making sure that the circuit is working, remove the battery and attach the development board to the battery holder on the double-sided tape.

20. Done

Step 20

“Joule thief” is ready to use!

Leave a Reply