|The ranging system
works fairly reliably, with only a few false updates. The distance measurement
appears to be accurate out to over a meter, though detection at longer
ranges is intermittent. It can track an object down to about 10 cm. Averaging
several of the last updates would produce a distance reading less prone
to jumps. The transmitter and receiver assemblies work well, but their
range is disappointing. Despite trying a variety of antennas, we were
unable to get reliable links past about 5 feet. We could try using a FM
transmitter/receiver pair, which are less susceptible to noise, but have
more problems with line of sight.
We also considered sending the data over the RS-232 link to a PC, which could serve as a data gathering mechanism. This would allow the device to serve as a distance/velocity/acceleration meter, using MATLAB to plot the curves based on the data sent.
We could also make several enhancements to the existing design. We would like to get the antennas tuned a bit better to operate at longer distances. The transmitter and ranger should be placed in a sealed, weatherproof shell for mounting on the front of a car. In addition, we could replace the sonic ranger with an IR detection system, which would be more resilient to the rough conditions encountered during operation on a real automobile.
There was also a lockup that occurred a few times on the receiver after using the calibration routine. However, we could not reproduce the effect or find a deadlock condition in the code.