I love Altoids. Too much. So I save all the boxes. One a month on average, sometimes more. I have over 100 lying around. I've made everything from a GoPro housing to a flashlight - so I thought I'd share the flashlight one.
Parts needed: Two 9v battery clips (not holders - most won't fit!), foam rubber (I used some stick-on window insulation), small rocker switch, LED dome-light panel. These are sold on eBay - a set of five is typically $9 with free shipping from China. These are great for a variety of LED projects and are one of my favorite components. You'll also need a few inches of wire, epoxy and soldering gun.
Of course, you're not limited to an Altoids box. I wanted a prop for a photo shoot - remember the briefcase from Pulp Fiction? Something like that but smaller - so I made another version of this, but in a small wooden chest. The switch is inset into the base. More photos at the end.
This is an exceptionally simple built. The LED panel has an adhesive backing - so it just sticks in the lid. There's typically 3" of wire on these. There's also around 4" of wire on the battery clips - if you're careful, you can use this wire for the project. You'll be wiring up the 9V batteries in series for 18V. This is the part you need to be careful with - if you wire them up wrong/short circuit them, you'll fry everything and possibly start a fire. It takes some effort to do that, but I thought the warning is worth it.
You can see from the close-up photo of the battery clips how the wiring is done. The negative from the light is hooked up to the negative of a battery clip, while the positive goes through the switch. I use heat-shrink on all my soldered wires. If you don't have any heat shrink, use tape. You need to make sure the wires are not bare and don't contact the metal box. You need a little extra so there's some slack when the lid is fully open.
The rocker switch can be purchased from almost anywhere - Amazon or eBay they are around 10 for $10. Again, a really handy component. You want to wire up everything outside of the box. Switch, battery clips and panel, and test. Once you're done and you verify it works, it's time to mount in the Altoids box.
Step 2: Mounting in the Altoids Box
Peel the tape off the LED panel, and press into the lid. You can eyeball it or draw some center lines. Press in place by pinching the LED panel and lid together, making sure to press all around the panel. Once in, it's in for good. Next, epoxy in the switch. Mix up some epoxy - I used 3 minute setting. Lay the case on it's edge - you want the epoxy to stay on the edge. Press the switch against the epoxy. I positioned it off center towards the front so the wires drop into the bottom. Use a small clamp to hold it in place. IMPORTANT - make sure no epoxy gets into the switch - it can glue the rocker and ruin it. I left it sitting on the edge of my bench until the epoxy dried. Go get some coffee and come back in 30 minutes. Read the set time for the epoxy - 3 minute epoxy will still pull free after 3 minutes. If you have time, let it sit overnight.
Attach the batteries and place them in the box. Now add foam until the batteries don't move around. Since the foam compresses, it can be a nice, snug fit. You can see the batteries pressing into the foam by a 1/4" or so on the top of the batteries. This is why I like to use insulation foam - it's thick and sticky. You can also use the adhesive foam hobby sheets that hobby stores sell, but those are only 1/8" thick. You'll need to stack the foam is you do that, and it does not work as well as soft foam.
How bright is this? It will light up a 12x12 foot room! It's also a great emergency or camping light. You can also cut out colored sheets (I used old report covers) and put them over the LED for colored light.
You can also get creative - I made a second version in a small chest ($5 from a craft store.) Two led panels. There was more room so I used battery holders and mounted the switch inset the base so whomever is holding the chest can turn it on from the outside.