Hello everybody!
Im slowly getting to the point where i need to test my project in large assembly mode, not just with some leds on a protoboard, but as a integrated whole.
So now im realizing that i didnt have a plan for this part of the project, somehow i overlooked it completely..
The project is a over-achiever-light control box for a vehicle (my recumbent bicycle primarily), that reads inputs(buttons) and sets outputs (mcp23008 i2c pin extenders), witch in turn are mounted on custom pcb´s that also has a bunch of 2N7002 FET´s to control external LED´s via pin terminals on the pcb´s.
All the pcb´s are designed for 5V input, and to control the power to the pre-existing lights via FET´s.
I also have some fuses (1-5A, 12V car fuses) and the plan to integrate a self-disconnecting circuit as the first step after the battery.
The self-disconnecting circuit is pretty much exactly like the one described >HERE!<.
But my idea is to "duplicate" parts of that circuit, to also control certain heavy consumers via the pin extenders (mainly the high power LED´s and thier drivers) in the same fashion.
So instead of a single-step circuit as the one demonstrated on the link above, im aiming for a 3-step circuit so to speak.
Step one, the one enabled by the powerON-button (no off-switch), enables the arduino, witch is used to keep the first step (MAIN) active.
The arduino then enables the second step, that powers the i2c chain.
The i2c pin extenders are then able to activate a 3rd step where required, controlling the power-thieves that drain battery even when not used.
The OFF-switch for the project is a software timer, 30 minutes since last function update, also a "if press for x seconds"-function on a certain button to kill the system, requiring a new powerON-button press to turn back on again.
Now, a voltage regulator isnt exactly expensive, and i have a few LM2940T-5.0 already, i could simply power each sub-segment of the project locally, with its own fuse and regulator.
But i could also have a centralized regulator to power the whole thing, however, that means i would have to have a separate power lead for the power hungry front lights anyways.
Concidering my 3-layered approach, is the best solution to power the arduino and i2c devices and LEDS from one regulator, then have a secondary regulator providing juice for those mad-dog front lights?
Any suggestions, thoughts or ideas so far?
Im not really sure how to proceed at this point, since my skills in electronics are self-taught, bare neccessities-basis..
I will (probably) not have concidered (insert your thought here), since im probably not even aware of it..
The battery is to be at minimum 6v, guessing max around 14v (system takes up to 28 i think), total system consumtion (when everything is on) is about 2,5A @5V.
Other details about the final installation;
I have a very wide tube frame on my recumbent, inner dimensions are about 6cm, or about two inches, so i will be fitting everything internally, eventually even the battery.
The installation locations are 4 in total; front tube (pedal fix point), handlebar and headtube, rear bike light housing and finally the trailer (disconnectable).
My current plan is to try out a regulator for the arduino and i2c, add the bike LED´s on a separate regulator and a third one for the front high power leds (cree xm-l t6 x2).
Im not sure this is the best approach, but i kind of need A approach, so.. 
Another part of my puzzle is where to put the fuses..
Should they be near the battery, or near the consumers?
Also, do i need any special attention to the fact that im running multiple regulators to power each sub-section, while still having common signaling (and by extension, ground)?
Ive seen capacitors being used pretty much in all "non-amateur" circuits, and theyre used in so many different ways that its hard for me to just "copy" a web-search-result..
So would anyone add cap´s into this project? if so, where and why?
i do have some, but they are kind of a mystery item to me, i know they work and some about how they work, but i dont know how they work in circuits.
