It's a small headlamp similar to lamps like Rude Nora, Scurion, El Speleo, etc.
The heart of this project is PIC 16F616 which contains two individual comparators used in step down LED drivers. Two CREE XP-G2 LEDs can provide up to 916 lumens, however due to the small body (heat sink), the output power is limited to 3W per led (about 600 lumens).
The body is made using aluminium alloy 6082 on a small lathe, the battery box is 3D printed (will be machined on CNC mill later hopefully).
After some time of using darkstar underground I came into conclusion the maximal light output is far from enough, especially when visiting big cave domes, etc. There's not many ways to increase output power on the board as the LED heat transfer through vias is far from perfect. The solution could be using cooper as base material for PCB, but that's an expensive solution. Also the driver efficiency is not very good, lots of energy is wasted on switching transistor and current measuring resistors.
These were the reasons why I decided to make a new, improved version. The basic operating principle stays the same (hystersis driven buck convertor), but that's all. New version will be powered by attiny (and finally programmed in C, not assembly) and will be designed for 2 A / LED current. Together with thee new CREE XP-L2 LEDS, the light output should be at bat-roasting level :)
After few months since the last log, the headlamp visited several underground places, survived muddy caves, dark mines, old tunnels,... Maximum output is much more than enough for most of the time, higher option would be nice for photography and bigger halls. I'm designing darkstar Mk.II as my bachelor thesis, so stay tuned!
Using two 18650 from old laptop battery, the headlamp is able to run on reasonable walking power (~150mA, body is completely cool) for 25 hours, then it went to emergency mode with 40mA consumption and worked for another 4 hours.
The charger was able to charge 3896mAh into batteries after this test.
Also, I measured the weight of the headlamp. The lamp itself weights only 80g! Battery box is 45g and the battery pack is 96g -> the whole project weights 221g.
Last thing missing is head strap and the project is finished! (Or I could just simply drill some holes to my helmet and use the screws to hold the lamp on its place. But I use the helmet for both caving and climbing, unmounting and mounting the lamp everytime I do a different sport would be pretty annoying...)
Thanks to Ing. Jaroslav Stepanek, I have measured the real light output on Brno University of Technology, Faculty of Electrical Engineering in integrating speher.
The expected value based on datasheet and measured current on full power was about 600lm, because of decreased efficiency of LED when heated and looses in optics and plexiglass cover, the real output was slightly over 200lm.
If you are interested in more details, check the github page!