Analog Sensor Suggestion

Good evening,

Can anyone suggest a low price (

It will help us if you can give details of the application and working environment for your system.

I´m building a vehicle proximity control system, that is, making my rc car maintain a predefined distance from the object in front of it. I was thinking of using an ultrasound sensor, my problem is that the ones I find are either digital or analog with an exponential behavior, which makes it a lot more difficult to control the tension applied to the motor in a linear manner.

Just a couple of ideas:

1) An IR LED (or array) on the back of the lead vehicle; the following car tracks it for steering, and detects its brightness for distance information. Use IR because the sensor can have a filter to exclude ambient light.

2) An ultrasonic emitter on the lead vehicle, direction and distance detected as above.
(However, I understand that dogs can hear ultrasound, so they may start chasing it as well.)

The exponential response may just be a result of the root mean square law, that a radiated signal is not received at a directly proportional strength to its distance. But this could be an advantage, because a very weak signal could be used to elicit a catch-up-quickly acceleration response, with a stronger signal reducing speed as it gets nearer.