Abstract: A portable braille display unit which presents an entire page of braille characters in response to data stored on a storage medium, such as a tape cassette. The display unit is the size of a conventional braille page, and the display unit may be made portable and self-powered. Each braille character is displayed by a braille cell display module in which spring actuated pins are controlled by bimetallic latches. Each module includes six pins which comprise the six dots of each braille cell. To display braille characters, an electrical current is applied to resistively heat selected ones of the bimetallic latches. In response to this current the selected bimetallic latches bend and disengage from the pin, allowing a compressed spring to move the pin upward through the surface plate to display a braille dot. The spring maintains the pin in this position without requiring power from the power supply.

Abstract: A circuit for measuring the relative phase of two periodic signals. Two analog waveforms are applied to limiting amplifiers which provide digital output signals. The output signals therefrom are applied to digital circuitry which provides an analog voltage representative of the phase difference between the two input signals over a 360 degree range. The digital circuitry compensates for any offset errors which may be introduced by the limiting amplifiers.

Abstract: An acoustic current meter in which two channels have acoustic paths oriented at right angles to each other to measure orthogonal components of a current velocity. Each channel includes two transducers aimed at an acoustic mirror so that the reflected acoustic signal from each transducer impinges upon the opposite transducer. Periodically, a burst of high frequency acoustic energy is simultaneous emitted by each transducer. A current flowing produces a relative phase shift between the received signals representative of the current velocity. The output signal produced by each of the transducers is mixed with a common reference signal to provide two, low frequency, beat frequency signals having a phase difference proportional to the current velocity. Due to the reduction in frequency, the phase shift is expanded in time with respect to the phase shift of the acoustic signals and may be easily measured.