Well, I've tried 2 ultrasound devices (1 cheap, 1 expensive (returned)), an IR device and I have played with do-it-yourself using the Pi camera and a laser pointer. I apparently have unreasonable/unrealistic expectations for these sensors.
I want to make a sort of "electronic cane" (size of a D-cell flashlight, no stick) for the visually impaired -- something held in the user's hand that's angled downward at a point 10' or less ahead. I want the rangefinder to be able to be read several times a second and (most importantly) detect walking surface irregularities of 2" or less at 10'.
Since the current Pi package is too big to wrap your fingers around (something more compact coming?) I'm using an Arduino Micro (which happens to be good with analog outputs, too).
The rest of the gear:
- the afore-mentioned rangefinder
- an accelerometer to read angle
- some sort of output to the user (currently 2 vibrating devices)
- on/off switch and battery
Back to distance measuring:
- Ultrasonic: basically, way too wide an angle of reception (but fast enough on the Arduino)
- IR: problem with the angle to the surface, especially a reflective surface (i.e., water puddle)
- Camera/laser pointer: (Google "Pi camera as rangefinder") Attractive on the Pi since I'd have control of the software BUT lots of problems: 1) no camera for Arduino (and it's not fast enough and not enough memory), 2) sunlight blots out return from a "class 1 laser" (one not dangerous to eyes) and 3) same reflection problems as IR.
Maybe my project is doomed.