I needed a head lamp for a place where I’m going to where is no light. It’s a place where no other people or other light sources are. So at night it’s really dark there. Also there are no stores in the area where you can buy batteries. Luckily there is power. So I made this head lamp which can be charged with a phone charger. The Li-ion battery charger PCB is very cheap and cost me 1,5 euro. The battery is a 4,2 volt type that I took out of a cheap Bluetooth speaker. The dimensions of the battery are 34,5x37x5,5mm. The capacity is therefore unknown. I used PET-G to make it watertight so the battery can’t get wet. That’s also the reason the power button is outside the case. Otherwise the water (rain) has an extra hole to get into the case. The LED is a 3W power LED in series with a 1 Ohm resistor. This LED is thermos glued to a plate of aluminum (diameter 46mm x1mm) to keep it cool. The “glass” is cut out of 2mm acrylic plate (52,9mm). The elastic band (24mm x 1,25mm) I got out of a tailor shop. Sewing is not really my thing as you can see :-)
The head plate is in 2 different dimensions and on the photo I used the smallest one.
Also the lamp is adjustable with a little M3x20mm screw. (you also need an M3 nut).
The reason the wire from the switch go’s all the way to the lamp and not directly inside the case is to avoid that water reaches the battery. Li-ion battery’s react very explosive to water :-)