Sensor Direction and distance

Hi. I am trying to make an revirsing sensor/display/audio for a wheelchair. My young person is unable to turn his head and revirsing is now an issue to him. But it needs to switch on when the chair is revirsing. This is the part that I am unable to do at the present. My options as far as the distance is easy and presents no problems to me. I have an LCD under the tray (clear acrylic) so he can see it with ease. Also a audio device. This is driven by the Arduino via wireless.The screen show's the rear of the wheelchair (draw on) with dots as distance and angle. The Angle comes from the servo output and the distance comes from the ultrasonic sensors. In the rear if the chair I have a servo scanning side to side with ultrasonic sensor on. This is also driven by an Arduino sending signals wireless.

SO how can I tell if the Wheelchair is revirsing ??

I have the arduino's,ultrasonic sensor,servo,audio device,wireless units and the screen. So far I have completed the Ultrasonic,Servo,Audio,Wireless and the LCD programming. Hope this makes sense to you.

Regards Antony

SO how can I tell if the Wheelchair is revirsing ??

The motors are going one way, not the other. Perhaps you could tap into the wiring, to detect direction.

As Paul says, if you can tap onto the wires coming to the drive motors, that will indicate direction.

Also, as a suggestion, you might try mounting 2 sonars on opposite sides of the chair pointing straight back, rather than 1 sonar on a servo. I think this will give more reliable readings, without having to compute angles. Also, these readings should be able to tell when the chair is backing up, and turn on the display.