Introduction: USB Rechargeable Eco Friendly Flashlight

About: I love the challenge of building unique things. My goal is to make technology fun and help individuals build the skills and the curiosity to experiment with some of the amazing technologies we have available t…

Help save the environment by building your own USB rechargeable flashlight. No more throwing away cheap batteries every time you want to use a flashlight.

Just plug into a USB port to fully charge and you have a powerful LED torch which lasts for over 2 hours of continuous use.

Step 1: Gather the Materials

  1. TP4056 Lithium Battery Charger Module Charging Board suitable for 18650 batteries
  2. 18650 Rechargeable Battery
  3. Access to 3D printer
  4. Hookup wire
  5. Vero Board - 9 x 5 holes
  6. Power switch Small SPST 6A rated
  7. High Power 3Watt LEDs 3.4V 700mA Cool White X 2
  8. Mini LED Lens 13mm 20 Degree Angle X 2

The high current rating on the power switch is important to pay attention to when purchasing the switch because the LEDs will draw over 1amp when the torch is turned on and most small switches have low current ratings.

Step 2: 3D Print the Case

The torch is printed in three parts

  1. Main Body
  2. Bezel
  3. Base

I used a Creality Ender 3 to print the components using the following settings

Filament: White PLA (Black PLA could be used for the Bezel)

Infil Density: 20%

Supports: For areas touching the build plate only

Speed: 60mm/sec

3D print files can be found here on Thingiverse

Once completed I used water-based black artists paint to paint the top of the base unit to minimise the degree of light shining through the body of the unit.

Step 3: Build the Circuit

Circuit Overview

The circuit uses high power 3W LEDs with 20 Degree Lenses to focus the beam providing a very bright and powerful little torch. The LEDs operate at 3.4-3.7v and the battery voltage will rise to 4.2v when charged. In order to limit overvoltage to the LEDs, I have put a heavy-duty diode in series with the LEDs which drops the LED voltage by 0.6v.

Note: Leave connection of the battery until the last step to avoid accidentally shorting out the battery. If this occurs the battery could overheat and explode.

1. Mount the LEDs

Cut the Vero board to size and check that it fits into the top of the torch body. Solder both of the LEDs on to the Vero Board being careful to ensure that Anode and Cathodes are connected together in parallel as per the circuit diagram. The LED Lenses have a 20 degree light angle which gives the torch better range and focus. Push these over the top of the LEDs as per the picture.

Note: Take care to orient the LEDs the correct way. The Cathode or Negative side of the LED is indicated by the Negative Sign cut out of one leg "-". Incorrect orientation of the LED will result in damaged LEDs.

Use hookup wire to connect the anode and cathodes of the LEDs with approx 10cm of length for later use.

2. Battery Charger

Following the circuit diagram connect approx 10cm lengths of hookup wire to the TP4056 board. Leave connection of the battery until the last step to avoid accidentally shorting out the battery.

3. Power Switch

Attach approx 10cm lengths of hookup wire to the power switch. I used Heat Shrink to insulate the connections to avoid short circuits when the unit was closed.

4. Install the Diode

I have included a 1N4007 diode in line with the LED to reduce the voltage to the LEDs by 0.7v without introducing resistance. Carefully connect this in line with power switch as per the circuit diagram and cover the diode with tape or heat-shrink to avoid shorting out to other components when the unit is closed up.

5. Connect LEDs, Switch & Charger together
Run the LED wires through the holes in the top of the torch body down to the base. Position the power switch and wires, checking that the switch pushes home neatly into the torch. Solder the connections as per the circuit leaving the battery connections to last. Connect the Battery charger output to the switch and the LEDs as per the circuit. Now you are ready to test the circuit. Ensure there is enough hookup wire to accommodate the connection to the Battery from the Charger.

Step 4: Final Testing and Assembly

1. Installing the Battery

Before initial testing ensure the power switch is in the off position. Carefully solder the positive battery connection then cover all exposed wiring with duct tape. Then, carefully solder the negative battery connection then cover all exposed wiring with duct tape.

2. Testing the unit

Now try turning on the torch switch, the residual charge in the battery should light the LEDs. If all is ok then attach a USB charger to the Battery Charger Board and check that the unit is charging correctly. When complete the battery charger light will change from Red to Green.

3. Mount the Battery Charger

Mount the Battery Charger board into the base unit using glue The best approach is to connect a USB cable to hold it in position, as per the pictures, then use hot glue on the underside of the battery charger PCB to fasten into position. Be careful not to overheat the case as PLA will melt easily. Leave to cool and harden before removing the USB plug.

4. Final Assembly.

Push the switch into the body and gently position wires so that the battery can push into the base. Check the unit will close correctly before using hot glue to fasten one side of the battery into the torch body ensuring it will not interfere with the charger PCB or the switch.

4. The Bezel

Push the lenses onto the LED. I recommend you either print the Bezel in Black PLA or paint it as I have to give a more professional finish. Push the Bezel onto the torch and it should fit snuggly without glue.

Now you have your own rechargeable torch, no more wasteful batteries that end up as landfill.