Bicycle taillight is important for every cycling enthusiast.There are two types:electroless and electronic.I prefer to electronic one.Because the led in the dark has a bright light to keep cyclist safty.So I made this project and installed on my bike.The useful feature is solar recharging.I bought a solar cell to charge battery.

Tools and materials list below:

• Tools needed：

hot melt glue gun

soldering iron

wire stripper

scissor

• Materials needed:

solar cell (4.5V 90mA)*1

lithium battery(3.7V 850mAh)*1

colourful LED*5

wire-wrap board*1

switch*1

IN4007*1

rubber band*2

3M tape

## Step 1: Solder LEDs on the Wire-wrap Board

Firstly,I nipped a wire-wrap board in the bench and broke off a piece of the wire-wrap broad.when you break off it,you had better wear gloves.Take care of your hands.

To make the LED light brighter, I find a snack bag that reflect light ,such as potato chips or tea packing bag.Of course,I cut out a piece of bag with scissors as large as the wire-wrap board. I put the LED pins through the hole of the wire-wrap.

To connect every LED's pins,I soldered the pins of LEDS as shown in the picture above.

## Step 2: Electric Circuit

I searched knowledge of battery on internet.Because it's important to calculate the runtime of battery.As we know:a 1-hour charge at 5A should deliver a 1-hour discharge at 5A, or a 5-hour discharge at 1A.But this is not possible because of intrinsic losses and the coulombic efficiency is always less than 100 percent. The losses escalate with increasing load, as high discharge currents make the battery less efficient.

So,I measured the current of LEDs.We can estimate the runtime of battery .I switched on.LEDs lighedt up and I used multimeter to measure the current.Now, I can calculate the max value of runtime.

## Step 3: Install

Now, we can install solar taillight on the bicycle.There are many ways to tie the solar taillight to the bicycle with bubber bands.I glued the battery to sloar cell with 3M tape and also guled the bubber bands to it.The last step is to tie a tight knot.

## Step 4: Test

Finally,turn on LEDs and exhaust power.Then put the equipment outside in the sun.Solar will charge it.You will see the LEDs light up brightly when you turn on it.

Nice. You can use a joule thief circuit to minimize the consumption of battery. Thus, extends the time before the battery discharge.