A slapping happy bicycle lamp.

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How can we possibly make another bike light? That wasn't what I was thinking when I thought of this. I was going through work from a college sketch class when I had an idea, a light went off. What if we combine a slap bracelet with a LED headlight? The tedious task of installing a bike lamp will be replaced with a fun "slap", and in seconds there will be a bike lamp mounted to the rider's handlebars.

This is simple. Bicycle lamps are complicated. How do we attach them? Slide it into a slot... screw on a mount... strap it to our head... So many different ways but isn't there a simple way to do this? In the spirit of the Knogs and Bookmans of the bike world, I'd like to create something just as simple that you can do it too.


Diagram for the electronics.

JPEG Image - 134.19 kB - 04/05/2017 at 07:08


  • 1 × Slap Bracelet
  • 1 × Mouse Pad With a rubbery bottom. 7.5" x 9" or smaller size.
  • 1 × Double Stick Tape Industrial strength
  • 2 × CR2032 Battery 3 Volt lithium coin cell battery
  • 2 × CR2032 Battery Holder Low Profile dip-style design

View all 8 components

  • We Have the Parts

    Ashley04/05/2017 at 06:24 0 comments

    The parts have been acquired from a closing Radio Shack in Pasadena. Total cost for the electronics components was around $3.75. This circuit design and build was done by twoducky.

    Here is the schematic layout. We are keeping it simple for the sake of prototyping:

    More details on what we did:

    3.6/6 = 0.6

    60% Ratio

    3.6 V = 40 ma R

    Our 3 Resistors:

    R1 = 40Ω

    R2 = 54Ω

    R3 = 36Ω

    The finished prototype design is nice! Switch the switch and the light turns on. Switch it back and it turns off.

    Next steps will be making a 3D printing a case for the electronics. But first, we must plan and design such case. It will be a square case with a lip for the board to sit on. There will be a protective area that will surround the LEDS and a place to mount the switch. Oh, and the top will slide off so that the batteries can be changed. Otherwise we have forever batteries.

  • Sketch Time

    Ashley03/28/2017 at 05:37 0 comments

    So I've been sketching some ideas for what this light can look like in a perfect world. Ideally, it would be either a flush and smooth form, or something fun and funky. I've also collected some parts that I'm going to use to create the light part. The printed circuit board may be larger that I had intended, but Radio Shack was having a closeout sale so I decided to give it a try.

  • Revealing A Secret

    Ashley03/18/2017 at 02:06 0 comments

    I've been excitedly thinking about this for a good portion of today's free time. I found a BuzzFeed article that spoiled the secret of what is actually inside a slap bracelet. I thought "curved piece of metal" only to find out that some actually use recycled tape measuring tape!

    I went on an adventure to find a tape measure so that I could make a slap bracelet for my bicycle handlebars to wear. By the third store I found the very last tape measure hidden in a pile of tools. Who knew tape measures would be in such high demand? Over the course of a couple of hours I tested the tape measure tape to create my own slap bracelet. It is mediocre and difficult to get the circumference small enough to stay on a bicycle handle bar. But it is a good start.

    For now, I have left the section of tape measure tape in a tightly curled coil to see if it will behave better next time. Otherwise, I'll be buying a traditional slap bracelet to try. In the meantime, I've ordered a mouse pad. This seems random, but I have a plan.

  • Getting Started

    Ashley03/17/2017 at 05:03 0 comments

    Where should we start? Back in my sketching class, I found the problem: attaching a bicycle lamp to a bike can be much easier than it is. Several years later and several minutes ago I found a solution. BAM..or slap? Something quick and something simple that we can all make.

    Does anyone remember these?

    Aside from making an interesting sound and occasionally causing a sting to my wrist, I don't know what made me acquire one into my possession. But now I have a reason to acquire slap bracelets. To begin, I'd like to do a survey of all my options when it comes to purchasing a slap bracelet online.

    I also looked into unusual bicycle lamps to see if something like this exists. I've researched more, but here are a few of the unique products.

    The next step is going to be for me to think about this, do some sketching, and decide on some parts to start prototyping.

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Ashley wrote 03/17/2017 at 18:16 point

That's a good idea. For this part of the project I'm prototyping how to physically fit a battery and LED with the contraction mechanism of the bracelet. I'm also not a fan of coin cell batteries for bike lights. Ideally, the flexing motion of the bracelet would power the bike light. But we will see.

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Martin wrote 03/17/2017 at 08:15 point

This is a funny project, but I do not like the concept of coin cell powered bike lights.

Why not have the bike light properly screwed to the bike and powered by it's motion? Cyclists want to be environmentally friendly and then they burn through countless coin cells just to have inadequate light.

The old fashioned 6V/2,4W (0,4A) incandescent bulb produced probably something like 30 lumen. This is estimated from the lumen/watt rating of a standard bulb with the same current (not power). Because the efficiency of light bulbs is strongly dependent on the current. A 230V/100W bulb (0,43A) produces 13 lumes/watt, a 25W bulb (1/4 of the current)produces only half of it, 7-8 limen/watt.

To produce 30lm with an LED you need around 0,3W or 0,1A which drains a CR2032 dead in 2h. I know that most of this lights run longer - because they are dimmer.

A modern hub dynamo has nearly no friction and you do not need to think about batteries.

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