All the cool kids agree - hands-free lighting is a good thing. But even better: combining custom-built lighting with head protection. I could subject you to an awful fake sales pitch, but instead I'll relate my experiences building a personal-area headlamp.

I'm on the road so you'll have forgive the absolute lack of pictures here. If you've seen me wearing a har hat in pictures lately, it's the lighthat.

Waterproofing is hard. I'd suggest gooping all electronics in something to reduce water infiltration. The SPDT (One wire, two positions) switch is not waterproofed at all. I think its metal bits are beefy enough to survive since they will also dry quickly. I built this with about $11 in electronics, so we'll see how it lasts.

I had two hard hats. One I set up to be fed by 3 AAs. I hate AAAs and had a Coleman 3-color flashlight head begging for a home. This one is heavier but has blue, white, and brighter white. The dim white will run for about 5 weeks, and the bright one for 5 hours or so.

But my favorite one uses 1AA and a boost constant-current driver. That's a circuit that raises voltage until it's pushing a particular amount of current through a circuit - in this case, nominally 500 mA. Since it weighs less I call it the LightHat. I changed that lazily, but let's talk wires first.

Power electronics need heatsinking, especially if they're covered in water-resistant goo. I soldered the LED to a copper endcap, and the driver to a copper strip. If you don't want to risk toasting the LED, use thermal epoxy because it can be almost as good. Reflow soldering involves heating the copper so that it has molten solder sitting, then putting the (dried!!) part to solder on, letting the solder wick onto it, and then cooling it before the temperature destroys your electronics. So, a brazing torch, tweezers, and an ice cube. The LED should be kept at about 120F for ten minutes to drive out moisture first.

So the hard part's done. After testing this at 500 mA nominal current, I decided that the LED was getting hot and putting out too much light. LEDs get less efficient at higher current, and each new lumen helps vision less. A camera would notice but I won't. I tried a 1-ohm resistor between the battery and the driver. Putting it between the driver and the LED would just tell the driver to produce a higher voltage. This cut the apparent brightness only a little and removed temperature problems.

I attached this copper assembly to the front of the hard hat with wires protruding. These go to a SPDT switch with two resistors on it - 1 ohm and 12 (that 1-ohm, then 2 22s in series) ohms. A switch in its middle position is often 'off', letting me make a 3-function 2-position switch. Finally, one AA holder powers the switch as follows.
An SPDT switch connects either pin to the center pin, and in the middle makes no connection.
Battery (+) to 1-ohm resistor to switch-middle.
Switch-1 to 11-ohm resistor to switch-2.
Switch-2 to CC driver input (+).
Driver output + to LED (+).
LED ground to driver ground.
Driver ground to battery (-) (Ground).

I'll be able to upload pictures tonight, if I'm up long enough to do so. So far the 'don't waterproof switches' has worked nicely.




<sub>After extensive testing in all conditions short of diving, the LightHat is ready to be shared.

Born from need and built from what I had lying around one night, the electronics feature state-of-the-art reflow-soldered heatsinks on all power electronics, a side-mounted bi-mode switch, and a lightweight single-AA power source. The Cree XR-E LED mits 80 lumens ('high' mode) of neutral-white light for 2 hours in a wide pattern optimized for close work. Low mode serves as a night-vision preserving level that will run for (calculated) 28 hours.

On low batteries, the LightHat dims to allow a battery change. To avoid damage to NiMH rechargeables, the boost driver disables continuous 'high' mode operation below 0.9v. 'Low' will run for several hours after this point is reached.

A modern and comfortable adjustible hard hat protects the front and top of the head from the impacts without interfering with heasring, and an anti-glare coating protects user vision. LightHat: proven endurance.</sub>

Surface-mounting LEDs is tricky if you can't make the whole bottom electrically neutral. With the Cree X (xr-e, xp-e, xp-g) line, the ends of the bare LED chip are positive and negative. To isolate them, sand the contacts gone, or just sand the corners of the chip. You can barely see the connection point on the upper surface.

This would have saved me some trouble building this. If you work with LEDs on stars, it's not helpful.

Hard to get decent construction shots on the road.

Heh, nice

I'll get some pictures together, but I've added an optic to the LED to give it better throw, and a hinge to aim a bit.

They sell baseball caps here that have lights built into them. They don't look as bad as you might expect them to either!

It looks kind of like this

Posted by Pteronym They sell baseball caps here that have lights built into them. They don't look as bad as you might expect them to either! It looks kind of like this http://panthervisi...ap-3-led-large.png

Baseball caps don't bounce concrete and rebar off my head though ;)

Nor do they look as cool. I added an optic to the lighthat so it throws better. I have been considering rebuilding it into a conventional headband I can throw on the hard hat, but that'll come in time.

Still works, never gets hot, has survived a few baths.