There are already several similar products at the market that combine an mp3 player and a headlight, nearly all are made in china, they are mostly good but very expensive. A model is sold for 95€uros here.
On the other hand, there are many headlights, hand torches and mp3 players which does their jobs very well and are very cheap. So I’ve concentrated on this deep :-) issue and designed an mp3-headlight-torch suitable both for bike and manual usage and costs much less the market products by using the parts of very cheaply available mp3 and lighting products.
Step 1: Requirements
Listening to your favourite music while cycling is nice. You don't want the music to be interrupted due to drained batteries.It is also nice to have the product do other duties like ligting in the smallest package coz bike handlebars are already full of other instruments nowadays.
Step 2: Design
First I’ve searched for cheap mp3 players. They are around 8-12$ and their performance is quite good, they even have radios and equilizers. I checked out many types, brands and shapes; rectangular ones, cubic ones, elyptical prisms etc. Some are bigger and stereo, others smaller and mono, having very similar designs, they all look like they have been manufactured at the same factory in China. Actually bought some 2-3 of them and started dissecting them, disassembled some, broke one or two completely, took out parts.
Then I've started sketching some designs based around the shapes and sizes of the mp3 players at hand. I've produced two stereo mp3 player holders first, didn't likethe first one, developed more organic shaped second one. 3d printed and tested it.
At the beginning I was planning to take out only the electronic parts of the mp3 player and use them in my own design and add the lighting circuitry and leds next to them. The mp3 players that I've first dissected were a bit large, stereo ones with remote controllers etc and they had 3-4 mini pcbs, big speakers inside, occupying quite large volume. So the computer sketches that I first did seemed a bit bulky to me and I've gave up that idea and instead planned to use a smaller mono mp3 player as a whole and purpose design a lighting module that will match it nicely forming a combo music-light product.
Later did some sketches combining the small mono mp3 player with my own light design, selected one of the designs and modeled it on Solidworks. While modeling the design also evolved, by new inspirations and ideas. Used a wide angle lens onto one of the 1W leds and a narrower angle lens onto the other. The wide angle lens was also turned towards the ground as a short beam lighting while the other led was projecting the light further ahead. I've made the necessary details on the design to be assembled to the cylindirical mono mp3 player. Nice Thing is this player having a small plastic base which is very suitable for being used as a interlocking part between my designed headlight and player itself.
Step 3: 3D Printing
Printed the body with an Up printer. Tested the parts for good fitting to each other and also to the mp3 player. Seems okay.
Step 4: Circuitry
Parts hacked from a cheap hand torch or our solar charged bike light project circuit can be used for building this product.
Our solar charged bike light project is a microprocessor (PIC12F675) controlled intelligent light with 9 lighting modes. Modes and lighting power can be changed by using two switches on the circuit. The runnning modes are;
1. Double 5mm led flash
2. Double 1W leds triple flash
3. Double 1W leds continuous flash
4. Continuous power 1st grade + flash/2seconds
5. Continuous power 2nd grade
6. Continuous power 3rd grade
7. Continuous power 4th grade
8. Continuous power 5th grade
9. SOS signal flash mode. Flashes S.O.S distress signal with 2 1W LEDs.
It has a power output for high power leds driven by a mosfet transistor and a weaker output for driving one or two 5mm white leds. There is the possibility of connecting a light sensor for the torch to operate automatically but on my product design I didnt use that sensor and there is no hole on the product for its placement. But a hole can be drilled easily.
There is a small tutorial on soldering on my robotics websites if you are new to soldering and circuit assembly.
Step 5: Assembly
I’ve completed assemby of the first prototype to actually see the possible problems in the design. I've found some and corrected / improved them on my solidworks files. The final design can be downloaded from this link.
I was planning to put extra batteries inside and make power systems of the mp3 player and the light separate. But as I wanted the final product to be as small as possible, I’ve looked for a way to use the mp3′s internal battery for both music playing and lighting. So I’ve disassembled the player, soldered a pair of wires to the battery terminals and took the power out for the light. I’ve drilled a hole at the mp3 player to let the cables out.
Step 6: Second Prototype
Later I've produced a second prototype. The quick release of the first prototype was not working due to its size was too small for my 3d printer's resolution. So I've modified and enlarged the quick release details. Now it works.
Step 7: Solar Power and Charging
Finally I've designed a mount to hook up a solar module to the bike. The design above came up. Being a bit bulky, It is quite strong, easily carrying the weight of the solar module, can carry even more. Later I've also added a detail to it for the headlight to be mounted below the module and carried by the solar module mount itself. The STL file of the solar module mount for 3d printing can be downloaded from this article.
I had several solar modules lying around at home that I've bought for other projects in the past. I've used one of them in this project, it is capable of generating around 7.5v open circuit voltage and 250mA short circuit current. This can easily charge the battery inside the mp3 player which is 3.6v. In sunny days, the panel can charge the battery while music is also playing, enabling me to continue listening after the sun goes down. A usb cable takes power from the solar module to the light-mp3 combo.
Step 8: Usage
Here is a video of us using our solar powered mp3 players during a MTB tour.