After staring at the original Honda navi documentation, I redrew the structure diagram to represent what I want.
This will be the brain of the entire navi unit. The current plan is to use the Atmel SAMA5 microprocessor. It’s an incredibly power efficient (~200mA at 500MHz) for the amount of work it does and it can run Android no problem for an in car display.
Honda runs a protocol called GA-Net on the physical layer IEBus. It transmits button and touchscreen presses and also some control over the audio unit. The biggest issue will be decoding the GA-Net protocol and figuring out what to do , This shouldn’t be difficult as much as time consuming. The IEBus Controller will have to be it’s own microcontroller that handles the communication scheme and talks up to the microprocessor.
The F-CAN which is Honda’s CANBus is the interface with the car’s ECM which provides us information such as battery voltage and fuel consumption. This is not critical data but it would be useful to pull for some sexy displays.
The + and – of the GPS Antenna is brought out to the navi unit over a connector. This will allow using almost any GPS chip as long as I impedance match the antenna.
The documentation for the original navi notes a somewhat physically large gyroscope being inside the navi unit. I think it’s funny needing such a large device. I will be placing two MEMs(Microelectromechanical systems) chips that will provide accelerometer and gyroscope data. I currently am not sure why the navi system would need this data but would be cool to have.
In the 21st century, microSD is easy to plop into a circuit and use, so why not add some memory expansion capability
For now the USB is only meant as a debug port to the outside world, being in the trunk doesn’t lend itself to providing anything cool to do with it otherwise
To make my car even better, let me throw it onto the GSM network with a sim card! Then I can get live google maps and traffic data.
The other parts of the diagram are what the navi unit gets from the car and are basically required to make it work, i.e. the audio-hvac display module. One thing to do note is me ignoring the XM Receiver, I have no need for it so I won’t waste my time with it.