Led driver

New version!

There's a whole new version with mutch more features and power: https://github.com/kajusK/Darkstar-Mk.II/

DarkStar headlamp

Small, lightweight and waterproof LED headlamp with two Cree XP-G2 leds. Can be used in biking, caving, mine exploration, hiking... But always carry a backup light source.

Features

• Waterproof aluminium lamp body
• Lightweight - whole headlamp, including two 18650 batteries, weights 220 grams
• Two 5W Cree XP-G2 LEDs with independently controlled brightness
• Always on LED with wide (115 degrees) beam to illuminate surroundings
• One narrow beam (10 degrees) LED to illuminate long tunnels, big caves, etc.
• Real Lab-measured light output is over 200lm (ebay value, based only on LED datasheet, would be over 600lm), see Measurement for more details
• Small red status LED (can be replaced by UV LED, etc.)
• Controlled by PIC 16F616 MCU (source code included)
• Low power off current (3,2 uA), no need to unplug battery during power off state
• Low power mode when battery is almost dead (single LED on lowest power, ~40mA)
• Long run time (up to 110 hours on lowest power (~40mA), over 24 hours on reasonable walking power (~150mA))
• 3D printed waterproof battery box for two 18650 Li-Ion cells

Weight

• Lamp head: 80g
• Battery box: 45g
• 2x18650 battery pack: 96g

Controls

• Connect headlamp to battery, LEDs will flash and device goes to sleep
• Press and hold up button for about 2 seconds, first LED turns on
• Use up/down buttons to increase/decrease LEDs intensity
• Press and hold down button for about 2 seconds to turn on/off second LED
• When the second LED is on, use up/down buttons to control its intensity
• Press and hold up button for about 2 seconds to turn the lamp off

Warning

Li-Ion cells can catch fire or explode if not handled properly. The hardware design was NOT extensively tested, the headlamp could die any time, don't rely on it as a single source of light.

The headlamp body can get quite hot if both LEDs are running on full power, there's no thermal protection, you have been warned.

License

This headlamp is provided under open source license WITHOUT ANY WARRANTY, see LICENSE for more details.

HowTo

Directories

• cad headlamp body and battery box design (FreeCad)
• pcb contains all kicad files including BillOfMaterials for electronics, please note plated vias under Cree LEDs are mandatory to move heat from LED to heatsink (body). Gerber files for manufacturing are included.
• pic contains assembly source code for the headlamp MCU

Electronics & software

For overview how the hardware works, check microchip application note and source code README.

To reduce manufacturing costs, the heat from CREE LEDs is transferred to aluminium body using several plated vias under the LED itself thus avoiding the need for aluminium PCB or big star heat sink for each LED. For some math background, check the Cree thermal management guide.

Power wires are soldered directly to the PCB. To program the MCU, solder wires to ICSP pins or build some kind of pin-touch interface. Use make in pic directory to compile the sources (assuming you are running Linux), you can use make burn to upload the firmware using pickit2.

Lenses

The wide beam LED can be used without lenses, the beam is wide enough for my needs, for the narrow beam LED you can buy any compatible lens (it will require some modifications due to limited space on PCB though). I used [17mm 10deg lens] (http://www.aliexpress.com/item/Free-shipping-cree-xp-g-lens-Diameter-17mm-Smooth-surface-with-stand-Condenser-lenses-10-deg/777222733.html)

Body

The body is made from a piece of aluminium 6082 T6 using a small lathe. The top cover is made from plexiglass taken from old diving goggles. Waterproofness is ensured by big O-ring between body and glass and two small O-rings on the control knob. The body works also as a heat sink for LEDs, therefore it cannot be made from plastic (e.g. on 3D printer).

The battery box is printed on 3D printer from ABS (I would rather use aluminium, but I don't have access to milling machine).

See Bill of Materials.