tablet to replace speedometer. auto turn on/off?
in my car, i have a diagnostic module, wich is basically an arduino, that reads all my sensors, does the neccecery calculations, and sends a string to my pc.
so far i had use my computer as speedometer. but since it takes forever to turn on, i find its better to use a tablet instead, in the place where my old speedometer used to be.
the tablet will be 9" (cause the only screen diamteres that fit my speedometers place are 7",9",and 12,3 " ), and i hope to receive the string from the arduino, via bluetooth comunication.
My main concern, is how would i make the tablet, turn on and off (i mean the sleep, wake that ARM proccecors do), when the ignition is turned on and off.
the only way i have though so far, was to hardwire the tablets button, to enother circuit that send pulses when ign is on or off, but this seems pretty risky, adn i would like a more non invesive way... something that would have to do with the tablet being charged or not maybe??
anyone have any ideas??or, has done something like that before??