Magicshine, bicycle front light, MJ808, MJ-808, MJ818, MJ-818, bicycle rear light, CAN bus, MCP2515, MCP2561

front and rear lamps do work together and can be used on a bike. logic unit and auxiliary devices are still WIP.

this undertaking is an attempt to redesign the MJ808/MJ818 lights by:

• designing a custom PCB w. driver/controller ICs,
• writing firmware the above controller IC,
• encapsulating the above in MJ808's/MJ818's original housing,
• combining:
• the rear light (MJ818),
• the front light (MJ808) and
• a control unit into an interconnected smart bicycle light system.
• developing further auxiliary devices which extend functionality of the lights.

== and || denote the CAN bus, power lines are omitted.

front and rear lights are interconnected via the CAN bus; the front light activates the rear light.

(front light) - (rear light)
------------------------------------------------
(mj808) ======  (mj818)

front and rear lights are extended in their functionality by other auxiliary devices interconnected via the CAN bus

(front light) - (control unit) - (rear light)
------------------------------------------------
(mj808) ====== (control unit)  ====== (mj818)
                  ||		||
                  ||		||		
                  ||	(future device(s))
                (dynamo)

google magicshine mj-818 / magicshine mj-808 for an idea what the lights are and look like.

these are decent made-in-china bicycle lights operated off a 2S2P Li-Lion battery pack.

their functionality, apart from producing light, sucks.

operating mode selection, strobing and high power consumption on the original lights is what i would like to have different.

the only reasonable way to achieve this is to start from scratch.

• eagle for PCB layout & schematics,
• atmel studio (or keil) for the code,
• atmel ICE or something similar,
• some cheapo arduino for quick and dirty CAN testing (the arduino acts as an improvised control unit) and
• SMD soldering equipment and skills.

• /datasheets/: contains what the name suggests,
• /dwg/: AutoCAD drawings & STLs of various sub-components,
• /eagle designs/: contains subfolders with eagle designs (.brd, .sch & BOMs) of various sub-components
  • cos/: a dynamo thing, WIP,
  • mj808/: the front light,
  • mj818/: the rear light,
  • mj828/: a small handlebar mounted UI (nothing fancy), WIP and
  • drawings for the atmel ICE <-> light PCB programming adapter.
• /eagle libraries/: contains eagle libraries of electical components used.
• /gerber/: gerber files for PCB production,
  • mj808,
  • mj818
• /MJ808/: C source code for everything.

look in /datasheets/ for a complete lists of used hardware.

core components:

• 4-layer PCB manufactured via OSH Park,
• Attiny4313 8bit microcontroller,
• MCP2515 CAN controller,
• MCP2561 CAN transciever,
• MAX16819 & MAX16820 LED drivers,
• LDK320 5V LDO,
• 0402 passives and
• Cree XM-L and XP-E high power LEDs.

when chosing components the primary criterium was size, since everything needed to fit into existing housings. maximizing light output to the extreme was not a design factor.

the language of choice is C, written in an object-oriented fashion:

• common core components translate into an abstract base class (implemented via C-structs),
• concrete implementations (e.g. mj808 ) translate into derived classes (again C-structs),
• methods are generally implemented via function pointers (e.g. CAN driver message operations),
• behaviour is sometimes achieved with OO interfaces,
• polymorphism is implemented manually via constructors (ctor in mj808_t) and
• information is hidden by nesting C-structs and placing them into either .c or .h files.

due to memory limitations there are only hints of SOLID and design patterns to be found.

code is commented in a reasonable manner.

TODO