Homebrew Headtorch

Jun 23, 2018

With my DofE silver practice expedition coming up I found myself firstly without a torch, and secondly wanting to outshine anyone who gazed upon me at night, interrogation style (or at least avoid being interrogated myself). Having seen the helpful video by DIY Perks on YouTube what seems like not too long ago (but is actually over 2 years), I set out to build my own, and succeeded in creating a mini sun that blinded anyone who came too close.

I began this project a while ago, planning to use the body and battery from an old otoscope, using the dimmer mechanism to do the same for the torch. The specs looked good, the super-efficient LED’s I had consumed less power than the old original LED in the unit. I had intended to 3D print an adapter part from the screw thread to my LED, and thereby preserve the handle/battery unit, however I didn’t end up getting round to it and had issues with the old batteries.

I first assembled the LEDs. I had thought about this design to wire three in parallel before, and got right to it. I ended up redoing all the soldering for this section, but the design remained the same. I only added a layer of clear nail varnish to insulate the solder joints against shorting with the heat sink.

The next part was the main wiring. I had a few switches form an earlier failed project, which conveniently had JST connectors on either ends of the attached wires. I opted to use this connector therefore, and preceded to solder a spare connector I salvaged from an old drone battery to my ‘new’ BEM7 d2 battery. I also ended up attaching two other pairs of wires out either side of the switch, one leading to another JST connector to plug into a voltage monitor and connect it when the switch was thrown, while another pair would this time connect a MicroUSB charging circuit to the battery when the switch was in the off position. Some fiddly soldering later and my rats-nest wiring was complete and functional. As mentioned, I chose to use a cheap battery monitor to prevent over-discharge as it was far simpler than a full-blown BMS that disconnected the battery, and was what I had laying around.

This was only three or four days from the expedition, so the pressure was on to finish the unit. I was struggling to find a suitable enclosure for the battery and wiring. I had attempted to use a heat-formed piece of PVC I had flattened from a drainpipe, but this did not go to plan. Luckily in the nick of time my dad threw away an old business card holder, which just happened to be the exact size of the battery with a little room to spare. I cut the required slots for my components, and held the two halves together with some small screws. Sadly it was polypropylene, so my attempts at mounting the voltage monitor with hot glue failed, however I was able to wedge it next to the battery to hold it in place, its readout being just visible through the white plastic (and even more at night). This was to be at the back of my head, and the heat sink & LED’s obviously at the front.

To hold the LEDs to the heat sink I laser cut an acrylic mounting plate and tapped some M3 holes into the heat sink, allowing some machine screws to press the LEDs into place. I then had the idea of extending this to also form the part that attaches to the elastic head strap and faces the head (the parts nearest the head are unsupported and have some spring in them. About half a dozen failed attempts later, and much patience form my DT teacher I had a working part and had formed it around the heat sinks. All that was required now was the head strap.

This was made form some elastic, which threaded through slits on both the fore-piece and electrics box. Due to the weight of the battery this was not properly supported, so a strap across the top of the head was added. This worked out nicely because the wires that connect the LED’s can be run straight across the top of the head. A few thread loops held them in place.

Voila! It was done and worked a treat on the expedition at night. I had hoped to spray the electronics box black, but haven’t got round to it. I found two issues- the first being the stress that the elastic puts on the electronics box, but I hope to look into finding/making a better box anyway - thankfully this issue was spotted now and can be addressed. The second is that the acrylic reflects some light out its edges and down into my eyes. I solved this in the nick of time with some aluminum foil, but I will look into creating a proper block to stop this issue. I also hope to add a dimmer switch as well, the blinding brightness is sometimes it’s downfall.

Overall I’m extremely satisfied with the outcome of this project, and hope to keep adding tweaks to further its usefulness.