I like to use our Rio Karma MP3 player in the car, but it's not nearly as good as it could be. So here are some jottings on what an ideal car dock would do for the player.
- Power and charge the player, of course
- Offer various options for sending audio to the car, including a built-in quality FM transmitter, a port for a special Cassette sized interface (more below) and various cables for car stereos that have an accessory jack (as mine has for a trunk CD-changer) or plain audio inputs.
- A wireless remote control to stick on the wheel (not needed if other remote control methods can work.)
- A microphone.
- To get really fancy, an 802.11 interface to allow it to sync up with computers inside the house while in the driveway. Though strictly, this would be even better inside the player, not in the dock.
The microphone would perform several roles. One, it would detect the ambient sound level in the car, and boost the music volume as the car gets noisier. No more super-loud when you start the car either.
Secondly, it would listen for the sound of the music the player is playing. It would try to tell if it was playing, so it could detect when the stereo is turned off or switched to something else, or when the car is turned off (if the loss of power from the accessory jack doesn't already reveal this.) When the sound stops (even if this takes 5 seconds to confirm) just pause the music back in time when the sound was first detected to stop. One could then from time to time send out pulses of the forthcoming audio, and if it hears them, treat that as a resumption of play.
In a very fancy system, the microphone could also offer speech commands to the player, if it has enough CPU to do this.
While ideally you would interface with the jack on the car stereo for control of an external player, one could also do some things with a cassette interface besides playing audio. For example, detect what the motors in the drive are doing, so you can spot if the user hits stop, FF, rewind, scan, eject or tape-reverse. All of these could become remote control commands for the player to do something logical.
Many tape players have a scan mode to find the next song. This can be seen by the read heads being engaged while the motor speeds up. Wait a second, feed the player silence and advance to the next track would be a good behaviour here. FF might go to the next album or next track.
Ideally, the vendor would provide this since most of the intelligence would be in the player, not the dock. In some cases, a 3rd party could build it.