Build Your Own Working Bino-Scope Unit



To greatly increase the sensitivity (by maybe 100x), replace the BPW34 with a phototransistor. We haven't tried this ourselves, so we can't recommend any particular phototransistor to try. Find one with a large active area if possible.

Another idea: build two sensors, install them in both eyepieces, and send the signals to stereo headphones. Then put an IR filter over one lens, and no filter (or an IR-cut filter) over the other (or perhaps magenta on one, and green on the other). Without any view through the eyepieces, this would be harder to aim, but it would let you HEAR THE COLORS of the light as stereo audio information inside your head. Multiple colors should sound like various "instruments" located in the "orchestra." If the light source was changing colors, this might sound very interesting. At the very least, it would give you more clues for recognizing mundane light sources. Incandescent lights would be loud in the IR earpiece only, while merc vapor lights would not.

If one of these audio photosensor circuits was attached to the eyepiece of a large telescope, would any interesting sounds be received? For example, the flame of a candle *sounds* like the low rush of a burning candle. If the nucleus of a comet contains wailing gas jets, occasional explosions, vibrating plasma, etc., perhaps some of the comet's reflected light will become modulated, and the original sounds in the comet's atmosphere could be extracted by the telescope and photodetector.

If the gain of our circuits could be raised by orders of magnitude, it might become possible to monitor the moon at new (dark) phase, and pick up tiny brief sounds of lunar meteor strikes. Their brief flashes would sound like clicks. Star-twinkle, if it contains moving interference fringes, might do more than make rumbles and thumps, it might "ping" or "squeak." Lunar occultation of stars also might create brief audio tones because of interference patterns. And if significant numbers of amateur astronomers start listening to the sky as well as watching it, perhaps unexplainable noises will lead to new discoveries for conventional (non-fringe!) science.

So far we've not encountered any mysterious lights. We have found that our single opamp stage doesn't give enough gain to "hear" the dimmest of the visible light sources without burying them in noise, so it's time to modify the thing. Extra gain stages, bigger initial gain resistor, a few tens of picofarads across the gain resistor to prevent oscillation, maybe a phototransistor replacing the photodiode to give higher front-end gain, and perhaps sacrifice low-freq response by making it AC coupled, so bright lights won't drive the opamp's output to the rails.



Start Listening to the Skies!

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