Part 1 Power Setup
Quick run down of what I'm dealing with. I have a 2005 Subaru Impreza Hatchback that I wanted to create a dedicated power supply port for and find a space behind the dash to house Arduino Raspberry Pi or Tessel 2 projects. I started by disassembling the center console starting at the stick shift and working my way up to the top of the dash.
Along the way I removed the ashtray and the existing car power port (cigarette lighter port) and noticed that the power harness also powered a small bulb that was illuminating the ashtray (car power port plugs on the left, bulb on the right).
I disconnected the assembly at the clip and checked the voltage running to the bulb, ~14VDC running off of the alternator, perfect for what I was looking for.
I snipped the bulb off of the assembly and insulated disconnects were crimped on (the bulb got the opposite disconnects so that it can be wired back in later for aesthetics sake). I chose to use 1/4 in. insulated male and female disconnects for quick and easy connections that could be modified later if my setup were to change. They create solid connections that won't vibrate loose but I can also unplug and remove the entire system in minutes with no exposed wires left behind.
At this point in the process I had to decide what voltage I wanted to output and how I wanted to create it from my 14VDC. If my system was purely Arduino I could stick with 14VDC (although not the recommended input voltage for an Arduino, and bounces in voltage from the alternator will create issues eventually in the hardware) but I wanted to also be able to use a Raspberry Pi or Tessel 2 if a project called for it. To accommodate all systems I decided to install a new car power port behind the dash (I know, not the best practice) and run the system off of a car power plug that had built in variable voltage output from 5-12VDC.
Now for some wiring. I started off knowing that I had to connect the 14VDC from the previous bulb location to the new car power port but I also wanted to be able to reinstall the bulb that I snipped earlier so that everything would look like business as usual. So I modified the wires to have splices part way up so that the bulb would pull its power off of the line before the car power port started changing voltages. Below I have attached images of the (-) lead being modified; I created a small splice part way along the wire threaded a second wire through the strands of the first, soldered the two together, and heat shrunk the connection.
The (+) wire for the car power port came with a fuse in-line, I placed the splice before it because the bulb doesn't need the extra fuse and the fuse will help isolate my system more.
I now had a simple setup that gave me an extra car power port behind the dash. The car power plug that I got from RadioShack also has switchable tips so I picked up a 2.1mm barrel (for Arduino) and a micro USB (for Raspberry Pi and Tessel 2).
The power source that I chose to tap off of was controlled by the headlight switch on the steering column, meaning that I either have to have running lights or headlights on for the system to be powered. This is fine most the time but if I wanted the system off when the headlights were on I had to unplug everything...not ideal. So I added a switch in-line to control the power supply more precisely. Below you can see the wired setup hanging loose in my car with the bulb and car power plug working.
After tinkering with the system for a bit, the toggle switch that I had originally installed started having connection issues internally, so I switched to a push pull switch. I mounted the push pull switch in an empty switch cover plate next to my parking brake (where heated seat controls usually go).
I ran the (+) lead through the switch so that it turns the system on when pulled out and off when pushed in.
Now I have a power setup that takes ~14VDC through a switch, then through a fuse, converts it to 5-12VDC and then can be used to power pretty much any system I can cram into my car (WOO!).