PaulF's 2002 Volvo S60 version 3 - the half watt system
For me, the fun I get out of the car computing hobby is all about the custom remote control of devices in the car. I've gone through a few revisions of always on systems and have never been able to say "this system will absolutely not kill my battery."
Brief history of my systems - I make it sound too easy here haha
Version 0.5 - Just a PC
- AMD based system with Micro ATX mobo
- No fancy microcontrollers/fusion brains
- Relays "cleverly" attached to different things to turn the PC on/off with no intelligent startup/shutdown controller and turn the amplifiers on etc
Version 1.0 - PC + Sheeva Plug
- Same system as version 0.5
- Addition of sheeva plug
- Sheeva plug was on 24/7 attached to 3g, hosting an access point and allowing for remote control
- Fusion brain attached to sheeva plug control devices
- Big access battery to keep the sheeva plug powered
- Plug into house at night to charge
Version 2.0 - Single, always on PC to replace both the PC and the Sheeva Plug from version 1.0
- Initial plan was to USB PandaBoard, decided not to due to tons of weird linux/arm bugs when using a full desktop OS
- Used a FitPC2 instead (~8 watt consumption vs ~5 for PandaBoard)
- Windows 7 + Centrafuse + custom control software, etc, etc
- No plugging in at night
- Fancy high quality sound system
- 30 watt solar panel
- Completely dead battery, always.
Now in theory, I can fight very, very hard and trim that power consumption, maybe get bigger, better solar panels, but I'm really not interested in that fight. I also know a LOT more now than I did even 2 years ago.
So, here is revision 3.0
The idea here is to use a microcontroller for the always on portion of the install. The microcontroller itself will be able to talk without any overkill full-blown computers. This should result in something capable of running off any standard car battery without fancy charging systems/solar panels/huge batteries. I have yet to decide what I want to do for the entertainment/nav computer yet - I can use the computers from my past builds, build something new, or go with a tablet. Either way, this is 100% flexible since it can communicate with all of the above.
The parts I've selected for the task are:
Microcontroller: The 5 volt Arduino Mega Pro
Reasons for selection:
- The Arduino makes life easy with its giant community
- The mega offers 54 digital I/O ports (I could control 54 relays if I wanted)
- Mega offers 15 analog inputs for reading sensors.
- The mega has 4 hardware serial ports, so no need for software serial when communicating with other devices (GPS, OBD2, Cell modem)
- I have a lot of 5 volt stuff, so I chose the 5 volt version instead of the 3.3 volt version
- I chose the pro version because it is all for through-hole soldering, and I won't have to deal with buying connectors or lose connections
- Increased RAM (8kb) vs the smaller arduinos will make programming easier
- Low enough power consumption (Measured @ 33mA on the 12 volt side of 90% efficient regulator)
- The pro version has no unnecessary components on board
Cell modem: Seeedstudio GPRS shield
- Designed specifically for 5 volt arduinos
- Of the devices I looked at, the sim900 module seemed to be the most versatile cell module
- Low standby power: 1.5mA
- Max power on US networks: 1watt
- The board offers additional digital I/O ports in case I decided to use a board without so many I/0s
- Communicates over serial vs most modems which use USB
GPS: Sparkfun's Venus board
- 20hz GPS updates!
- Full power: 90mA@3.3 volts = .3 watts
- Reduced power: 60mA@3.3volts = .2watts
- Nearly no power in standby mode, 1 second resume time if it hasn't moved
I plan to attach this guy to both the microcontroller and the computer (via usb/serial converter) and be able to use it for both at the same time. This thing seems superior to anything available in the CarPC community for GPS.
Cell plan: T-Mobile "Unlimited Text and 10¢/minute"
- All I need is texting to get commands to/from the car, when I'm in the car I have my android phone tether for 4g
- Unfortunately, T-Mobile service sucks
- $15 is the cheapest unlimited texting-only plan I could find
- Other option was to add a line to my verizon family plan for $10/month, but verizon is CDMA and VERY picky about what devices are on their network
- Texting doesn't require nearly as good of service quality as internet does
- I can couple it with an awesome roof-mounted antenna for better service
- Plug & Play - just stick the t-mobile sim card in my GSM modem and it works.
I'm fairly well along in this project, so pictures and updates will come in a few minutes.