Lightweight Headlamp From Cheap, Readily Available Parts

Night skiing is really popular where I live, and while the ski resorts are adequately lit on piste at night, they are, obviously, not lit in the trees. Well, just because I can't manage to get to the resort during the day doesn't mean I shouldn't be able to enjoy a little tree skiing. Most commercial headlamps contain at least one if not more deal breaking issues, prohibitive pricing being one of those deal breakers. Home built headlamps can be really good, but often the designs I see online require the use of a lot of tools and ample shop space. Some of us are liberal arts majors who spend all our meager income on lift tickets and/or can't manage to hold on to one job long enough to afford to live in a house with a shop.

I don't have access to a CNC machine, a shop, or fancy tools, so I set out to design a headlamp that could be built in a spare bedroom of an apartment out of readily available parts that didn't require exotic tools or materials. Everything is available online and at either a good hardware store or a hobby shop.

The other considerations I had in mind are size, water resistance, and the ability to pocket the battery pack. The light runs off an inline resistor rather than an electronic driver so the input voltage can be 4.2 volts, which is the output of 4 rechargeable AA batteries. This is important because we skiers have to keep our batteries in our pocket so they stay warm, which means they have to be in a small enough package to fit inside a ski jacket pocket alongside snacks and a cell phone without making the skier look like a conspicuous shop lifter.

I also wanted the cabling to be cheap, detachable, and intrinsically strain relieved. That meant using RCA plugs for the power connectors so I could just use audio cables for the interconnects. This also obviated the need for a switch as I can just disconnect the cable when I want to turn the lamp off.

The whole assembly needed to not cannibalize straps and stuff from other headlamps. This meant I had to come up with a helmet mount that tilts as well. On top of tilting, it also needed be adjustable with gloved hands and able to be locked in place once at a satisfactory angle. I kind of like my solution, which is to utilize big ol' brass wing nuts and brass machine screws.

Here's a video of the headlamp in action at Skibowl.

My first headlamp used a heatsink from an AMD Athlon 750. Well, since then processors have gotten increasingly powerful and no longer have heatsinks that are small enough to mount on a helmet. But, as processor heatsinks have increased in size, so too have the heatsinks mounted on the southbridge chipset, which is the littler one 'south' of the processor on the motherboard. So, when my partner's motherboard blew up, I scrounged the southbridge heatsink from it.

The first thing to do with any heatsink is to degoop it. The best way to get that adhesive plastic off is to scrape it off with a credit card. Try to use a sideways sawing motion to get it to curl up. It really helps to soak the whole thing with isopropryl alcohol to soften things up a bit before scraping.

After getting the adhesives off, use some of the most advanced degreaser available, dish soap, to clean off the thermal grease. I'm not joking about the dish soap. I've tried a lot of different chemicals, and nothing beats a good surfactant that's up to the task of getting bacon grease off of pyrex.  

This is where we build the bracket that allows the headlamp to tilt up and down.

I use brass plate for everything, in this case I even used brass hardware. This has nothing to do with steampunk, rather, this has everything to do with durability and workability. I could end up with a lighter weight end product by using aluminum, but I can't solder to aluminum, and for this project I needed to be able to solder. 

First, mark out where the edges of the heat sink are and make lines. Your heat sink will differ in size from mine, so I'm not giving you measurements.

After you have the initial two lines drawn, grab the brass screws you'll be using and decide how much clearance the screw heads are going to need so they don't interfere with the heat sink. In my case I decided to give them an extra 5mm of clearance.

Remember geometry? That's where you should have learned how to locate the center of any quadrilateral. Well, you'll need a 1/4 inch hole in the middle of two quadrilaterals before making the 90 degree bends. After locating center, drill the holes.

Clamp the strips of brass in the bench vise and bend them 90 degrees. Try your best to make this a straight bend, while accepting that without the proper tools for working sheet metal, this is unlikely to happen. But that's okay, because we're working with pretty sloppy clearances here anyway, so nothing has to be perfect.

You'll also want to drill two holes that #4 screws will fit through in order to attach the bracket assembly to the heat sink. You don't really need to be exact about these, they're going to be obscured by all the silicone goo you'll be spreading all over everything.

This is where the 15 dollar pencil torch I just bought came in really handy. You'll want to use a torch for this, and lead free solder since you'll no doubt be touching this part of the project a lot. The best way I can explain the soldering process is to show this video:



Keep in mind that the dominant idea here is to heat up the brass first and use it to melt the solder. Also, understand that solder flows in the direction the heat is coming from, so try to keep the flame opposite the solder.

Now, locate where the holes in the heat sink should be. In my case, I decided to mount the light a bit near the top and screw the bracket on over the grease spot where the old south bridge chip set was. Figure out where it should go, then mark the spot and drill. This would be a good time to get the light and lens assembly and use them for placement. I went two bit sizes smaller than my tap because aluminum is soft like butter, so it's better to make things tight.

After drilling the holes, tap them. If you don't want to invest in an entire tap and die set, stop being a cheapskate and do it anyway. I got my cheap set from Harbor Freight. It works just fine.

I forgot to make provision for a connector. This is my fix for that error. You'll notice this light has no on-off switch. That is intentional. It's one less thing to break. I made this extra U shaped piece of metal and did some more soldering. Don't do this; it's a mess!

Here's where I shot myself in the foot. As you can see, the LED is mounted on an aluminum disk. After it's glued to the heat sink, that disk becomes capable of absorbing a lot of heat. The leads I soldered to the disk were only meant to be temporary, so I didn't do a very good job. My mistake. When I tried to resolder them after gluing things down, it got interesting. The heat sink kept sucking all the heat out of my soldering iron tip, so much so that the iron actually got stuck to the solder pad.

The solution is is not to have this problem in the first place by giving yourself some leads before gluing the thing down. The workaround is to solder very quickly.

As for gluing the LED down, just follow the directions on the thermal epoxy. The only one I disregarded was clamping. Since the disk has such a large surface area, clamping isn't really necessary. Surface tension does the trick.

Use solid core insulated wire to make the connections. This is because the wiring will be semi exposed, and if it flexes it will eventually break the solder joints. That is definitely what we don't want. I tucked the wire into the heat sink fins to hold it in place.

You'll notice I used a resistor instead of a driver. The resister cost me 20 cents from Mouser and works just fine. Yes there is some power dissipated in the resistor, but the light is still plenty bright and runs for 5 hours, so I don't really care. Simpler is better!

If I were running more LED's with more current I would definitely use a driver, but since I am only feeding this off 4 nimhs at 4.2 volts, there is not much dissipation in the resistor anyway. This is the other reason for the resistor instead of the driver circuit: I can get away with a lower voltage source. For a skier this is important because we have to keep our batteries inside our jackets so they stay warm. Anything larger than 4 AA batteries is too bulky to fit in a jacket alongside a cellphone and snacks.

Get some silicone and start squirting. Be sure to fill in every gap possible and overlap the edges of the lens assembly to ensure that no water gets inside. Doesn't it look nice and cozy in its silicone jacket? Yeah, it is ugly. But at least it does the job.

For my next headlamp, I'm going to be brainstorming ways to make it prettier. I may have to move away from the use of a heat sink and toward square tubing of some sort. I don't know, we'll just have to find out. What I do know is that this is effective. I get lots of comments when I take this skiing and people want to know where they can get one, but they often mistake it for a helmet cam at first. Another issue I'm trying to work out is the battery pack. I would like something a bit more robust. I need something waterproof that remains pocket sized. Any ideas anyone?