Ultrasonic Distance Meter

Octcber ULTRASONIC DISTANCE METER Until well into the twentieth century, most devices developed for measuring distance worked on the same principle: comparison of the measured distance with a standard unit of length. Other means are now available. One of these is the measurement of time taken by a sound wave to cover a certain distance. This sound normally lies beyond human hearing. The ultrasonic rangefinder presented here is suitable for measuring distances between 25 cm and about 6 m. The measured distance is shown on a 3-digit liquid crystal display-LCD. The low current drawn by the unit makes battery operation possible: a `LO BAT" reading on the LCD indicates when the battery needs to be replaced. The block schematic in Fig. 1 shows the four major parts of the meter: a sender, a receiver, a timing and time reference section, and a counter with display. The transduction element emits bursts of 12 pulses at a frequency of about 40 kHz. This frequency is roughly ident- ical wi...