Bicycle Helmet Safety Light II

Background:
I commute to work on my bike and I know that the automobile drivers aren't always on the look out for cyclists when it is dark.  I have noticed that cyclists even with a good handlebar light, can be over looked by drivers especially coming up on intersections with parked cars in the area.   The advantage of a helmet light is that it is high off the ground and most of the time is higher than the tops of most cars.   When your handle bar mounted light is being blocked by the parked cars, the helmet mounted light can be seen over the parked cars and other traffic.   This is critical when approaching intersections.  This light does not use any type of lens and the beam angle is quite wide.  This helps keep the light simple yet still effective since it can be seen from a wide angle by car drivers.

One disadvantage I see with typical helmet mounted lamps is that no one has discussed the potential safety hazard of having a ridged, bulky unit mounted to the front of your helmet.  A bulky lamp is just the opposite of what you want mounted to an impact absorbing bicycle helmet.   What happens in case of head on crash to the protection that is supposed to be provided for by the helmet when it is compromised with a bulky and strong head lamp?  With my Alien Eye blinker I was always concerned about the glass that the lamp was made and what would happen to it in a crash situation.   The original Alien Eye also has a very strong aluminum casting, and was already too bright for street use. 

        Safety Light II                       Safety Light I                    Alien Eye I                  Alien Eye II Blinker           

With these thoughts of safety in mind, and just wanting to play around with the newer inexpensive flat G4 LED assemblies, I cobbled together the Alien Eye III safety head light.   To keep the size and mass down, I decided not to integrate a blinker circuit in the light.   The blinker extends battery life and improves visibility to drivers, but complicates the packaging of the lamp.   A blinker circuit could be made and plugged in line at the battery pack end.  The light with cable and two part epoxy mount weights just 12 grams.  A small 12V 900 mah LiIon battery to mount on the rear of the helmet weights 89 gram.

This light is not intended to provide lighting for the cyclist to see but rather provide a low intensity wide angle light so that the cyclist can be seen by pedestrians and automobiles.  This keeps the light very simple, light weight, low cost and very easy to build.   The light is very small (22 mm in diameter and 7 mm thick) and is not mounted with a ridged system. There is no glass or bulky metal parts.   In an emergency the light can easily "break away".   This why I call it the "safety light"..

The LED is a G4 LED, 12V, 40 mA/ 0,48w, cool white 7000ºK,  20-25 lumens, Ø 20mm, 5mm thick

I bought the LED from Reichelt in Germany for 3.95 Euro   You can find similar ones on Ebay.   

To weather proof the LED chip I made a cover with the smaller half of a 19 mm coin holder. (Air tite, Leuchtturm) You can buy these at your local coin shop for 50 cents or so.   The edge of the coin holder was chamfered with a pen knife to better mate with the rounded edge of the metal LED housing.  The LED will set inside the coin holder but will not bottom out in it.  There will be a small gap between the LED chip and the coin holder face.  

The back of the LED has an aluminum base for a heat sink.    Using a magnifying glass I could see the housing, circuit board, heat sink were sandwiched together and appeared to be sealed with resin or epoxy material.    Since the LED appears to be sealed from the sides and back and the LED was too thick to fit in a coin holder, I just used the one half to seal the front and protect the exposed LED chip.  

The lamp is held to the helmet using double sided Velcro and and small crimped button snap.  The lamp angle can be adjusted by how the lamp is positioned with the Velcro on the helmet.  The button snap was used since the two part epoxy does not not stick well to the Velcro.    The male part of the button snap was fixed with two part epoxy putty to the lamp base.  The female part of the button snap was riveted to the thinner 10 mm Velcro.   The 19 mm Velcro is too thick for the button snap rivets I had.  The female snap side was riveted to the "loop" side of the Velcro.   The non-functional side of the female button snap is on the "hook" side of the Velcro.   The 19 mm Velcro is wrapped around the helmet with the "hook" side touching the helmet.

Materials for the project:  LED, 19 mm coin holder, epoxy, two part epoxy putty, shrink tubing  2.4Ø x 10 mm, 4.8Ø x 10 mm, wire, and double sided Velcro (19 mmx140 mm and 10 mm x 60 mm), 5.5x2.1 90º connector with 300 mm cable, crimpable button snaps.  Cost.  about 5 Euro with out the battery.

Assembly process: 
Chamfer the inside edge of the smaller half of the 19 mm coin holder.
Mix a small amount of epoxy glue.
Apply a small amount of epoxy on the edge of the coin holder 360º
Position the lamp on the coin holder.   Level the lamp.
Let the epoxy set up.

Cut 60 mm from the 10 mm Velcro.
Punch a 3 mm hole in the middle of the 60 mm Velcro strip
Center the Velcro, "hook" side down, over the snap half with the teeth
Press the Velcro over the snap half until all the teeth are poking through
Position the second half of the button snap over the teeth
Crimp the parts together.

Mix a very small amount of two part epoxy putty.
Place in the center of the lamp.
Press the male part of the snap connector into the putty
Smooth the putty around the snap, remove any putty from the snap inside edge.

Fabrication of the light:
  

Chamfer the inside edge of the coin holder with a pen knife

Punch 3 mm hole in the middle of 60x10 mm Velcro.   Assemble and crimp the female button snap.
Rough the aluminum back with sand paper.   Wipe clean. 
Mix the two part epoxy putty and fix the male button snap to the center of the lamp.   

Bend the terminals starting 1-2 mm from the heat sink.
Place heat shrink the 4.8 mm Ø heat shrink tubing over the cable.  
Place the  2.4 mm Ø heat shrink tubing over each lead.
Make sure the terminals do not touch the aluminum!
Wrap the connector wires to the terminals. +/- does not matter since the light has a bridge rectifier.

Solder the connections.   Move the 2.4 mm Ø heat shrink tubing over each joint and shrink.

Move the 4.8 mm Ø heat shrink tubing over both leads and shrink.   Check snap function.   

Mounting to the Helmet: 
  

The 19 mm Velcro is wrapped around the helmet with the "hook" side touching the helmet.

Stick the 10 mm Velcro with female button snap to the 19 mm Velcro.  
Snap on the light check the angle of the light while wearing the helmet.

The light is turned on simply by plugging it in the battery pack.  
The 12 V LiIon pack is in a bicycle inner tube with electrical tape, velcroed to the helmet back side.