Brief description of the unit
The electronic and optic components are mounted on printed circuit boards and they are, together with two AA batteries, contained in an aluminium case with the outer dimensions 160 *37*27 mm. The receiver lens and the laser are located at the small end of the unit.
The weight is of the order 200 grams. The unit can be clamped to the cane and adjusted for different "holding" angles. The mean current consumption is of the order 80 mA indicating a battery lifetime of about 12 hours for rechargeable NiMH batteries.
The laser source
The laser is a small diode laser emitting red light with the wavelength 670 nm. The mean power level is about 0.5 milliwatts. The LOAVI is classed in laser safety class 2.
In laser safety class 2 there are no safety problems and no restrictions regarding the use. The emitted light is shaped by optics so that a vertical line can be seen if the light hits for instance a wall, see figure. The total spread angle is 20 degrees. (Compare to the normal case where the laser light is shaped as a collimated narrow beam forming a small dot when hitting a wall).
At the front end of the device there is an optical receiver "looking" in the same direction as the laser. This receiver is only sensitive for light from the laser that is reflected in objects in the environment like the special bar code signs. The receiver is sensitive enough for detecting a standard bar code sign at 10 to 15 meters distance.
The signs contain 4 vertical strips of retroreflecting material (the same material as on many road signs) mounted on a plate with outer dimensions 270 * 110 mm.
The strips are wide or narrow like normal black and white bar codes. When the vertical laser line is moved over the sign pulses will occur at the receiver output. These pulses are interpreted by the microprocessor as combinations of short and long pulses (ones or zeros). A special beep is heard from the unit when the microcomputer has interpreted the signals as one of 16 barcode combinations. If the user presses a button a spoken pre-recorded message associated to the combination is heard from the unit. The pre-recorded messages are today:
"One, two, three, four, five, six, seven, eight, nine, door, men, women, store, elevator and information"