In emergency a small light source is a must. You may need it to find a more reliable light source like an operational flashlight. This flashlight is built around a super capacitor and a DC motor. Super caps can store up energy fast and release it slowly. These features plus their compactness make them so useful to build emergency flashlights. One can say: Hey, there are quite a few “shake-it” and “pump-it” models available at reasonable prices. That’s true, but my flashlight is a bit different. 1- minute finger spinning gives 5-minute lighting. You may opt to charge this flashlight with a string loop.
Time: 1 hour
Step 1: Materials and Tools
1. A small plastic bottle. Mine is a container for vitamin C pills. It is large enough to accommodate a DC motor and other parts.
2. DC motor. Mine is a 9V motor salvaged from an old cassette recorder.
3. a short length of insulated wire.
Electronic parts: 1 super capacitor (1F/5.5V), 1 super bright 5mm white LED(50cd), 1 – 24 Ohm/0,25W resistor (red-yellow-black), 1 Schottky diode (1N5819), a micro slide switch (3-pin).
Drill and drill bits (optional)
Step 2: Schematic
There are only 5 electronic parts : a super bright 5mm white LED (50cd), a resistor (24 Ohm), a Schottky diode (1N5819), a super capacitor (1F/5.5V), a micro slide switch (3-pin). The resistor limits the current flowing across the LED. The diode prevents discharging across DC motor’s windings.
Step 3: Prototyping
Solder the parts according to the schematic. Be sure the switch is off. Spin the rotor shaft with your thumb and index finger. Be patient. It takes about a minute to charge the super capacitor. Switch on and check how long it works.
Step 4: Making the enclosure
Remove the label and grease from the plastic bottle. Make a hole in the bottom. I used a hot electric wire and a file to do the job, but you may drill. The diameter should be equal to the diameter of your DC motor’s body. Make a hole right in the center of the bottle cap (5mm in diameter to insert the LED). I used a hot nail to do it. Make 3 tiny holes on the bottle neck to install the switch. I used a small hot nail to prick holes. The enclosure is ready.
Step 5: Assembly
Insert the motor and the LED into appropriate holes. Install the switch on the bottle neck. Solder the parts according to the schematic. You are done.
Step 6: How to charge with a string loop
If you don’t want to be bothered with finger spinning, you may try to charge with a string loop. Take a length of strong string (about 2m.) I think a dental floss will work ideally in this case, but I used what I had at hand. Make a loop and wrap it around the pulley on the rotor shaft. Place the flashlight on flat surface and press it with your foot. Tighten the loop and insert a stick (a pen or a pencil) into the other end. Pull hard downwards on one branch of the loop. Make a dozen of pulls and your flashlight is charged. By the way, string is a must in any survival kit.