Introduction: Old Toothbrush Becomes Rechargeable Flashlight

By
About: There are some things you should just NEVER do.....

Turn that Old Toothbrush into a Rechargeable Flashlight

Getting a new electric toothbrush and wondering what to do with the old one?

Don't dispose of it. Turn it into a rechargeable flashlight that is always charged and ready to go!

The size and shape of an electric toothbrush handle perfectly matches that of a hand-held flashlight.

This instructable will walk you through the transformation from toothbrush to flashlight.

It's not as easy as it might appear. Besides the mechanical challenges, this project includes circuit board modifications, addition of an electronic switch and voltage booster - all to reuse an old toothbrush!

.

This instructable will marry an old Sonicare rechargeable toothbrush with an LED flashlight from the Dollar Tree store. Let's all hope it's not a shotgun wedding!

.

A note on the flashlight: The LED flashlight being disassembled for this instructable is one of the best flashlights I have seen at a Dollar Tree store. It has a 100 lumen main light utilizing a parabolic reflector and also a 50 lumen wide-area side light. It runs on 3 AA batteries, which gives it more energy capacity than flashlights running on the smaller AAA batteries. The main LED is on a 'star' aluminum heatsink circuit board and runs at 1.5 watts. The only gripe I have is that the power switch is ON-OFF-ON making it too easy to turn on the side light when trying to turn off the flashlight.

This flashlight will be cannibalized, but get another one to have on hand as this is a great flashlight. And at $1.25 this is a bargain. [I did not receive any compensation for this endorsement ;-)] (Note: Dollar Tree now charges $1.25 for items - a victim of inflation and tariffs on Chinese imports).

Let's go upcycle this toothbrush into a rechargeable flashlight!


P.S. If you find the Instructables I post interesting please click the "Follow" button above. Thanks!

Supplies

  • Old Sonicare toothbrush (Model HX5250, but many of the similar Sonicare models may work). The toothbrush should be in working order. If you are replacing it because of poor performance or if it will not hold a charge you should not consider using it, unless you want to also replace the rechargeable batteries during the modification (Battery replacement is not covered here).
  • Charging Stand for Toothbrush, No point in doing this if you don't have the charger.


  • LED Flashlight,provides the LED, Reflector, Bezel. Model 317638 from Dollar Tree (UPC 639277928177 Greenbrier International). ---> UNFORTUNATLEY it looks like Dollar Tree discontinued this flashlight. They replaced it with one the looks somewhat similar, but has a smaller diameter reflector and a lower output LED. I'm saddened by this development. Dollar Tree should have kept it as part of their $5 offerings<---


  • Mini Pushbutton Power Switch Board, Push-on Push-off Electronic Switch circuit board from Pololu, Item #2808 This little board turns a momentary button push into a latched Push-ON, Push-OFF.
  • DC-DC Boost 5V USB Converter Board (Amazon) This board converts the 2.5V of the batteries up to 5V for the LED. It also current limits the LED.
  • Block of wood (approx 7/8" x 3/4" x 5/16")
  • Hook-up Wire
  • Hot Glue
  • Super Glue
  • Clear Thin Plastic Sheet (from a retail package)
  • White Spray Paint
  • White Silicone Caulk
  • Soldering iron, solder and hand tools

Step 1: Break Open Case

This is the most difficult part of the whole upcycle.

In order to modify the toothbrush you have to get inside it. This is not easy as the handle is entirely sealed around its perimeter.

To open it the two halves must be pried apart. This can be done with a couple of flat-head screw drivers. There is a notch at the top of the handle that will allow a small screwdriver to be inserted. Start there prying the halves apart.

As a gap is created insert the larger screwdriver to hold the gap open and work the smaller screwdriver around the perimeter of the handle. Eventually the halves will pop apart.

Step 2: Check Batteries and LED

No point in turning a poorly functioning toothbrush into a poorly functioning flashlight. The toothbrush should only be modified if it was operating acceptably.

It is a good idea to check the voltage of the two rechargeable nickel-metal-hydride (NiMH) batteries. Charged cells should measure 1.25V each. The voltage across the two cells in series should be 2.5 volts or very close. I saw 2.6V after charging, but it settled down to 2.5V after some time passed. I also saw 2.4 volts, but that should be OK also. Lower voltages may also be acceptable, particularly if a long time has passed since the toothbrush was recharged and it was operating properly when retired. Lower voltages can be a result of self-discharge of the batteries over time.

I also wanted to check the LED in the flashlight to verify its operating parameters. I connected a voltmeter across the LED and measured 3.56V with the LED operating. I also connected an ammeter in series with the LED and measured 0.43 amps (430 mA) with the LED operating. This means the LED is drawing 1.53 watts (VxA=W). Not a shabby flashlight. Because the LED needs a voltage drop across it of 3.56V (note the supply voltage is actually 4.5V [1.5V x 3 AA cells]) and our NiMH batteries in series only put out 2.5V the voltage will need to be boosted to power the LED. This will be done with a voltage booster circuit board, explained in a later step.

Step 3: Remove Circuit Board

We want to keep the circuit board as we need the charging circuit and charge status indicating LED. I also wanted to continue to use the toothbrush's existing on-off push button which has the charge status LED shine through it. To do this the circuit board needs to be removed and modified.

There are 4 solder connections to the drive motor winding at the top of the board (near where the brush head would be) and 2 solder connection at the bottom of the board where the charging coil is.

These 6 solder connections need to be desoldered. I suggest using a 'solder sucker' in order to remove as much solder as possible in order to remove the board.

Step 4: Modify Handle to Accept LED Assembly

The body of the toothbrush also needs to be modified.

The top threaded portion of the handle is cut off in order to shorten the distance from the lip of the opening to the 'bulkhead' flat surface inside the top of the handle where the LED will be mounted.

After cutting off the threaded portion of the handle the interior needed to be cleaned up and smoothed with a Dremel tool to remove all obstructions so that the wall thickness was uniform.

Step 5: Modify Toothbrush Circuit Board

As noted earlier I wanted to retain use of the existing ON/OFF button and charge indicator LED since it looks nice and has the charge status light shine through it. The LED is left as-is but the switch is more of a challenge.

Using the button to turn the flashlight on and off is another matter as it needs to be removed electrically from the existing toothbrush circuit. To do this the circuit board traces that go to the button need to be identified and cut to disconnect the button from the rest of the existing toothbrush circuit.

Taking a close look at the button one can see circuit board vias (holes in the circuit board that take circuit trace connections from one side of the board to the other). These vias take the buttons contact connections from the top (front) of the board to the bottom (back) of the board.

Cut the copper traces where indicated in the photos. You can do this with making several passes with a razor knife or with a Dremel tool.

After the cuts are complete the switch is isolated from the rest of the circuit.

The switch wires to the Pololu switch board will be soldered to one via on the bottom (back) of the board and another wire to another via pad, also on the bottom (back) of the circuit board.

The Pololu switch takes that momentary button push of the existing button and turns it into a latching switch; Push-ON, Push-OFF. It's a great little board and I could not have used the existing toothbrush button without it.

Step 6: Remove Drive Coil

We need space where we can locate the electronic pushbutton printed circuit board and also the boost printed circuit board. The drive coil, which is no longer used, is taking up a lot of space so I decided to removed it to make space for the circuit boards.

I originally thought that I would have to disassemble the coil as it was glued into the case with what appeared to be epoxy. I started cutting the coil windings in order to pull them out bit by bit and to my surprise when I grabbed the windings and pulled the whole coil came out in one piece.

Now we have a nice relatively large clean space for the added-on circuit boards.

Step 7: Modify the USB Boost Board

In order to have the boost board (low volt to USB, 5V) fit better in the available space the board has to be modified. The USB receptacle (connector) is bulky so lets remove it. Use a screwdriver and wire cutters to pry and cut the metal shell of the USB connector off of the circuit board along with the internal insulator. The part of the circuit board located under where the USB connector had been serves no purpose. So let's cut off the excess board so it we more easily fit into the space where the motor drive coil was located.

Four of the original circuit contact fingers of the USB connector will be left. Only the two outer connectors will be used. They are the positive and negative power. Cut the two inner contact 'fingers' flush with the circuit board. Cut the two outer contact fingers close to the circuit board, but leaving enough sticking up so you can easily solder wires to them.

Step 8: Harvest LED and Reflector

Unscrew the ring (bezel) holding the lens assembly and remove the ring, lens and reflector. Unscrew the battery compartment cap. The halves of the flashlight will separate exposing the LED star-shaped circuit board. Opening the flashlight was a heck of a lot easier than the toothbrush! Cut the wires to the LED circuit board. We will not be using the rectangular circuit board with multiple LEDs on it. Save it for another project.

Step 9: Connect Switch & Boost Boards, and LED

The electronics need to be assembled. Make the following connections. Following the diagram for reference.

.

CONTROL CONNECTIONS:

Switch circuit pads on the Toothbrush Circuit Board to connections 'A' and 'B' on the Pololu Switch Circuit Board. The connection polarity, or order, does not matter.

.

SWITCH BOARD CONNECTIONS:

The electrical power for the LED circuit is pulled directly from batteries at their connection point to the toothbrush main circuit board where the batteries are soldered. Solder wires from the battery terminals on the toothbrush circuit board to the Pololu Switch Board; positive to VIN, and negative to GND. The connection to the battery terminal should be done on the battery tab close to the battery so that the toothbrush circuit board will be installed over this connection.

.

BOOST BOARD CONNECTIONS:

Pololu Switch Board VOUT to the USB Boost Board + connection.

Pololu Switch Board GND to the USB Boost Board - connection.

.

LED CONNECTIONS:

USB Boost Board out - (negative) contact (The negative out contact is on the same side of the board as the negative in connection) to the LED Board - (negative) terminal.

USB Boost Board out + (positive) contact (The positive out contact is on the same side of the board as the positive in connection) to the LED Board + (positive) terminal.

The connections to the LED are just temporary tack soldering so the arrangement can be tested.

.

TEST

Test that the circuit is connected correctly by pushing the toothbrush button on the toothbrush circuit board. The LED should light. If it does not, check circuit operation by pressing the on/off button on the Pololu Switch Circuit Board. If still not light, double check the voltage of the batteries. They should be close to 2.5 volts. If still no luck retrace the circuit connections.

After successful testing disconnect the LED board as the LED wires will be going through holes in a plastic wall before being permanently connected.

NOTE: With the circuit assembled I checked the electrical parameters. I saw 3 volts across the LED and 112 mA of current (0.112A). This only gives me 0.334 watts going into the LED. Nowhere near the 1.5 watts in the original Dollar Tree Flashlight. I am not sure what is holding back the power. Obviously I am adding an electronic switch board and also having to boost the voltage (2.5V vs originals 4.5V) so there will be some losses but I did not expect the power output to be that much lower. However, I will say that the flashlight is still very bright and VERY usable!

Step 10: Cut Threads Off Old Flashlight; Glue on New

We want to be able to use the ring (bezel) that holds the reflector and lens in place on the Dollar Tree flashlight on the new toothbrush flashlight. The easiest way to do this is to cut off the threaded end of the Dollar Tree flashlight.

With the bezel in place, wrap tape around the body of the Dollar Tree flashlight. Remove the bezel and apply tape on the threads; the halves of the flashlight should stay firmly together. Cut the threads off of the Dollar Tree flashlight where they meet the body of the flashlight.

The threads will be glued onto the end of the toothbrush. (This whole modification was done because the threads fit perfectly over the flashlight.) To glue the threads in place the reflector and lens should be installed into the bezel and the threaded halves held together and threaded into the bezel. The Bezel holds the cut thread halves together while glued into place on the handle body. I applied transparent tape (aka Scotch Tape) to the back of the reflector to prevent the epoxy glue from gluing it in place. When gluing the threaded halves onto the toothbrush make sure the split in the flashlight threads lines up with the split in the toothbrush case. Use epoxy glue to fasten the thread halves to the toothbrush handle.

Step 11: Make a PCB Support and Glue It in Place

The toothbrush circuit board needs support under the pushbutton. The drive motor coil was removed so there is nothing supporting it. Cut a small piece of wood to support the circuit board. The wood will be as long as the plastic bobbin of the drive coil is tall. Cut out a notch in the top of the board so it will not interfere with the red indicator LED soldered to the bottom of the toothbrush circuit board. The bottom of the wood piece will need to be narrowed down to fit down into the bottom of the case where the drive motor coil was. Hot glue the wood support so it straddles the red LED.

Step 12: Mount Circuit Boards and LED

Mount the circuit boards with hot glue. Squirt glue on the ends of the boards.

The Pololu board is mounted on end (vertically) to the bulkhead (vertical wall) next to the batteries. The USB boost board is mounted in the bottom of the motor drive coil horizontally close to the Pololu switch board.

Drill holes for the LED wires in the bulkhead (vertical wall) where the LED will go.

Thread the positive and negative LED wires through their respective holes and solder them to their respective positive and negative circuit board pads on the LED.

Step 13: Cut New Lens

The height of the reflector is a bit too tall for the distance from the LED to the top edge of the toothbrush body (handle tube). I actually should not have cut off as much of the toothbrush body as I did. Since the reflector sticks above the toothbrush body a gap shows between the smooth top of the handle and the bottom of the bezel.

The best way to close the gap and move the bezel downward was to reduce the height of the lens/reflector assembly. The easiest thing to do was to replace the thick original lens with a thin sheet of plastic cut from product packaging.

Find a non-scuffed plastic package, trace the original lens and cut it out.

It fits where the old lens goes, but is thinner. The unsightly gap is virtually gone.

Step 14: Paint the Flashlight Bezel White

The flashlight will look nicer with a white bezel instead of a black one. I used a plastic primer paint followed up with white. It looks much better now that it is white.

Step 15: Install the Reflector and Close Up the Body

Line up the two halves of the handle and hold them together while you insert the reflector. Line up the small opening in the reflector so that it goes over the LED. Place the new thin plastic lens over the reflector and screw the bezel in place.

I used some super glue on the bottom end of the handle to help hold it together. There is a small gap around the circumference of the handle. Some white silicone caulk can be used to fill the gap in the two halves and hide any pry marks.

Step 16: Charge and Shine Brightly

Keep the flashlight on the charge stand to it is ready to go anytime.

The Sonicare manual states, "If the battery charge of your toothbrush is too low, … the charge indicator LED will flash rapidly for 30 seconds. When the handle is placed in the charger, the handle LED will blink slowly. When the Sonicare is fully charged, the charge indicator will stay on.

So charge your flashlight and keep everything bright wherever you go!

Enjoy!