Jameco Electronics Puzzler Solution: Secure CommunicationBy: Forrest M. Mims III
Secure Communication Between Two VehiclesJake Whispers was familiar with maritime signal flags and briefly considered color-coded signal cards as one possible solution. He quickly rejected this idea for having too little bandwidth and being distracting to employ. He then thought about the loud speakers employed by police cars to order motorists to pull over. But this method would not be secure and might even confuse other motorists. The best solution occurred while he was driving and the right tail light of the car ahead began flashing.
Jake immediately recognized that the turn signal employed red LEDs due to their immediate on and off state as they flashed. (Incandescent lamps do not instantly switch on and off due to the thermal lag of their filaments.) LEDs can be voice modulated, so LED tail lights can double as voice transmitters while also serving as day/night tail lights. For more power, one or both tail lights could be fitted with a voice modulated near-infrared LED.
The receiver for the truck would be a silicon photodiode installed behind the radiator grill. Taken together, this approach would provide a very secure means for the escort vehicle to send instructions to the Jameco truck driver.
What if the Jameco truck driver wants to send secure messages to the escort vehicle using a method as secure as the escort vehicle-to-truck method? One approach would be to install voice-modulated white LEDs in both of the truck's front parking lights or a near-IR LED behind an opening in the radiator grill. Silicon photodiodes for the escort vehicle's receiver could be installed in the tail lights of the escort vehicle if the photodiodes can be shielded from the tail lights to avoid saturating them when the tail lights are switched on. Otherwise, one or more photodiodes could be installed inside holes drilled into the rear bumper.