Tactile VU Meter

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[photo: the VU meter with its cover removed and shown next to a standard cassette tape for scale]Blind individuals are frequently employed in the radio broadcasting or recording fields, and even those who are not often want to use a tape recorder as part of a home stereo system. Unfortunately conventional VU meters, both analog and digital, are completely inaccessible to those without sight. There have been attempts to make accessible VU meters using various audible indicators, but in a recording environment audible indicators have never been practical.

Pagers have long used small motors, about 1" long and the diameter of pencil, with an eccentric weight mounted to the shaft as vibrators. The motivation for this project was the idea to use one of these pager motors as an annunciator in a tactile VU meter and, to be completely fair, this idea originated with Bill Geary at the Smith-Kettlewell Eye Institute in San Francisco.

The rest is simple. Half of a dual opamp is used as a buffer and signal conditioner for the audio, and the second half as a comparator. When the audio signal exceeds the comparator's threshold the vibrator motor is triggered. The gain of the buffer stage is adjustable via a small trimmer pot and is used to calibrate the VU meter so that the motor triggers at approximately 0 VU. The entire thing is powered by a 9V battery and fits into a box about the size of a pack of cigarettes.

Best of all, no software (and in fact, no microprocessor) is required!

The most difficult problem in this project was finding a suitable enclosure that could be carried in a shirt pocket. Fortunately PacTec makes a small one that was almost right and, after designing a custom PC board to fit this enclosure, a little plastic work is all that's needed to make a perfect fit.

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