ATtiny controlled magic eye tube

In the early days of broadcast radio, the most expensive radio sets were extremely impressive pieces of furniture. With beautifully crafted wooden cases polished to a high shine, these wireless receivers were the focal point of any family room. Some of the most expensive radio sets even included a visual indicator signaling the strength of the reception, something [Marcus] decided to re-engineer using an ATtiny85.

The display tube in question is an EM800 magic eye tube, used in radio sets, stereos, and electronic test equipment as a rudimentary display indicator. By applying a control voltage (from 0 to -10V), the illuminated display can be controlled like a bar graph display.

[Marcus]‘ tube display is built around an ATtiny85 microcontroller, using a homemade PCB. It’s a fairly simple build, once the issue of supplying 250 Volts to the EM800’s anode is taken care of.

In the video after the break, you can see the bar display of [Marcus]‘s magic eye tube slowly growing and receding, perfect for either displaying the current CPU load on your computer or anything else a dynamic bar graph display would be used.


  1. Ian says:

    The DM70 (AKA CV2980) might prove to be a more economic device as it was designed to be used in battery portable equipment.

  2. FrankenPC says:

    My dad built a Heathkit stereo receiver with one of these. As a kid I was in awe at the sophistication of the magic eye.

  3. rj says:

    It’s a a little sad he didn’t have any more bits in his DAC to drive it with; somehow the quantization makes it look too much like an LED bar graph to me.

  4. Marcus says:

    It can be operated smoothly, the usable range is about 100 different positions. The Video only shows steps of 10 !

  5. Galane says:

    These would be great as VU meters or use 10 or so of them as an analog audio spectrum display.

    Much cooler than a bunch of LEDs.

  6. AC says:

    Sure electronics has similar EM87 tubes for a while

  7. Marcus says:

    A spectrum Analyzer wouldnt be to difficult.
    Just program the Tiny85 to detect one particular Frequency with its ADC Input (Goertzel or Wave Digital Filter or whatever) and do this for 8 different Frequencies. There are even implementations of FFT for Atmel controllers…

  8. AussieTech says:

    One of the most common applications of “magic eyes”, or electron-ray tubes as they are known, was as recording level or VU indicators in tape recorders. They are more robust than a moving coil meter, much faster in response, and were available in a range of display formats.

  9. Philippe says:

    I just don’t see where the high voltage (250V) comes from.

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