This AVR ATmega8 based radar range finder project uses infrared light instead of ultrasonic. The project is built to detect sound absorbing materials like padded furniture which can not be detected by ultrasonic radar. Ultrasonic ranging systems require many milliseconds of acquisition time rendering them unusable for fast moving systems.
The range finder described here can make a measurement in sub millisecond time frame. It can detect a white sheet of 8.5 by 11 white paper at a distance of a few feet. Not only does it provide a range reading to the target, it also measures the reflectivity of the target which can further help the system determine the type of object.
Reza Miremadi, the project designer, explains that the device works by sending a 40ns pulse of light through a infrared LED every 35usec. The returned light energy is detected by a photodiode. The signal is then amplified and goes through a variable attenuator. A loop assures that the output of the attenuator is a pulse of fixed height. This pulse is compared to the original transmitted pulse and the time difference between the two determined. The time difference is proportional to the distance to the object since light travels at approximately 1ns a foot. The automatic gain control voltage is used to detect the amount of energy coming back from the device. This information can help determine the reflectivity of the object detected.
Project Detail and Documentation