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
Price: $45
Url: http://www.sparkfun.com/products/11007
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
Price: $60
Url: http://www.seeedstudio.com/depot/gprs-shield-p-779.html

• 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
Price: $50
Url: http://www.sparkfun.com/products/11058

• 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"
Price: $15/month
Url: http://www.t-mobile.com/shop/plans/p....mc_t=OnsiteAd

• 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.

Attached are pictures of the Arduino

Attached are pictures of the GPRS/GSM modem

Attached are pictures of a really ugly relay board I made, but it will be in a project enclosure, so who cares? :)

The chip on the front is a ULN203A - darlington array which allows the microcontroller to control the relays.

The relays are mixture of relays I had lying around, they are powered by 5 volts, and can switch loads at 12 volts, 5 amps.

It should be noted that I'm supplementing this with a pre-made relay board with 4 relays on it.
Url: http://www.amazon.com/SainSmart-4-Ch.../dp/B0057OC5O8
Price: $15

All of it attached

Current progress:
At this point, I've written ultra-reliable functions for sending/receiving SMS messages from the modem. If the modem is having trouble, it gets restarted, I can turn it on and off on demand to save power, etc.

I've implemented the commands "ON" and "OFF" which control the relays. Ex if I text the modem "ON:1" relay 1 will turn on.
In general, there is a 6 second round-trip time (includes command processing and time for response text to reach my phone)

The plan is to write an android app on my phone which will send/receive those text messages since the complex ones will be pretty cryptic since I'll be packing a ton of data into the 140 character text messages.

I'm waiting for the GPS shield in the mail, and figuring out what to do about OBD2.
The OBD-II UART modfule from mp3car looks pretty cool:
http://store.mp3car.com/MicroOBD_200..._p/com-141.htm
I may or may not decide to connect the microcontroller to OBDII though since presumably, if the car is on, the main computer will be on and be able to talk to OBD2 itself.

Almost forgot. Attached is a picture of a multimeter measuring milliamps of the whole setup. That's right, 44.1 mA @ 11.52 volts while attached to GSM. During SMS receipt/transmission, it increases to up to 60mA. With relays on, it, of course, eats a lot more power.

That's pretty awesome stuff. I especially like how you routed your programmer wires through the power plug hole in the Mega Pro :) I am actually embarking on a similar project, but using a small RF transceiver rather than a cell modem so I can communicate with my car when I'm within a couple hundred feet. Probably going to be using just a regular Arduino Uno since I have one laying around. Ultra Low power consumption ftw :)

One thing that I know tripzero did with his car, and I know I'm going to do with mine, is set it up with current sensors (sparkfun has some hall effect ones, not cheap though) to measure the solar panel and car computer. This would allow you to keep track of how much power you are using for your system. Not really especially useful, but another cool piece of information to know :)

Really nice relay board. I use the ULN2308A darlington drivers for switching relays all the time. I never even thought about trying amazon for things like relay boards though, that's a really good deal. Usually I just go for futurlec.com, but they take 3-4 weeks for shipping since it comes from china, and you always have to check the boards for build quality :/.

Very awesome! I lost my fusion brain... so I'm trying to think up a good reason to use the arduino (prolly a smaller one like the uno). I use the hall sensor one for higher current things like what's going into my second battery when it charges. I'm using smaller current sensors (also from sparkfun) for the lower current stuff like the solar panel.

That relay board looks quite awesome. I may have to check it out.

Great project. I would love to see a LTE modem but I doubt we'll see one anytime soon. I'm going to check out that GPS you posted. I already have a USB GPS installed but having one that I can share with my on board Arduino would be nice.