The amazing Pete Friedrichs has posted a cool video on how he used spinning green LEDs and simple electronics to create a modern version of a “magic eye” vacuum tube. He writes:
So-called “magic eye” tubes are display devices, which indicate signal level by the projection of wedge-shaped shadows on a glowing view screen. They were developed in the 1930’s for use as tuning indicators in radio receivers, and as alternatives to the then-expensive-to-manufacture meter movements.
Because they haven’t been produced in decades, and because they degrade and wear out with use, the supply of functional eye tubes is dwindling. I thought there might be value in coming up with a potential substitute– something that acted like an eye tube that could replace them in applications like antique radio restoration and general experimentation.
It turns out that convincing eye tube behavior can be simulated with one or more LEDs mounted on a rotating disk. The electronics to drive the LEDs amounts to little more an an op-amp, a transistor, and some timing components.
This video demonstrates the appearance of a real eye tube in operation, and introduces the principles involved in simulating one through electro-mechanical means. The video shows that the display generated by the electro-mechanical equivalent can be fairly convincing.
If you’re not familiar with Pete’s work, you must check out his website. He’s the author of two amazing books, Voice of the Crystal and Instruments of Amplification. I review both of them in the forthcoming issue of MAKE. I’ve heard raves about these titles for years. After finally getting them and reading them, I know why. Self-published, too!