Magic Eye Relatives

    Past and prsesnt, the appearance of a display on any device is a very important factor relating to the purchase of a product.  Whether or not the function of the display is essential to the operability of the product is irrelevant.  The colors and lighting schemes of digital stereo displays, dashboard lights, appliance control panels, and the like are undoubtedly important factors when marketing a product.  Shown here is a small compilation of devices that either led to the development of the magic eye, or mimick the operation of a magic eye.

silent tuning

"Silent Tuning" was an option that would mute noise while tuning in between stations.  The circuit at the left uses a neon tube with four electrodes.  The stronger the station, the higher the neon glow rises in the tube.   When the neon glow reaches the top electrode, the audio stage is enabled.   Because this circuit was employed years before the magic eye, I tend to believe that the person designing the circuit had intentions of surpressing unwanted noise, only to discover that the circuit doubled as a visual tuning indicator.

The "Shadowgraph"  was basically an apparatus similar to an analog meter movement that would cast a shadow on a small translucent screen.  The illustration (right) shows the various elements of the shadowgraph:  A..display screen   B..deflecting vane   C..ferrous disc   D..permanent magnet   E..electromagnetic coil
The deflecting vane is mounted at a right angle to the ferrous disc, which pivots on the two small points along its circumference.  There is a rectangular cutout area that allows light to pass through the disc, surrounding the control vane.  When voltage is applied to the coil, the ferrous disc pivots as a result of the magnetic field created, in turn causing the contol vane to no longer be perpendicular to the screen, thus creating a wider shadow.
Philco Console with Shadowgraph Tuning Indicator

shadowgraph

dial lamp indicator

This particular tuning indicator uses a dial lamp as an indicator, where the current flow through the bulb is controlled by a special transformer.   The stronger the signal being received, the dimmer the dial lamp gets.

This circuit uses a three element neon tube which operates in a similar fashion as in the silent tuning circuit (top), however the function of this neon tube is strictly as a tuning indicator, and has no other function pertaining to the radio set.  This was known as a Flash-O-Graph, or Tune-A-Lite.  See the other neat tubes section of this site for a picture of a Tune-A-Lite tube.

flash O graph

Pioneer analog reverb with special display

This Pioneer reverb had a neat display.  Remind you of anything?  It was made with ten pieces of glass, each one silkscreened with white ink in an oblong shape, gradually decreasing in size, and a light for each piece.   Imagine an oblong 6T5 with ten discrete display levels.