Mind Grenade

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Author: John Walker

Founder of Ratburger.org, Autodesk, Inc., and Marinchip Systems. Author of The Hacker's Diet. Creator of www.fourmilab.ch.

4 thoughts on “Mind Grenade”

  1. “Colour: In 1969, you could get LEDs in any colour you wanted, as long as they were red or infrared.

    Today we have no such limitations, and checking “Multicolour” changes the display into eight colour LEDs which show the current state and two previous states of each of the nine bits of the shift register.”

    I remember my Physics professor in the early 60s describing a new discovery that a properly biased diode would emit infrared (I think that was all) light.  “Of course, there is no real use for this feature, but isn’t it interesting”

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  2. WillowSpring:
    I remember my Physics professor in the early 60s describing a new discovery that a properly biased diode would emit infrared (I think that was all) light.  “Of course, there is no real use for this feature, but isn’t it interesting”

    The history of LEDs has largely been about figuring out how to obtain shorter wavelengths.  The first LEDs were infrared.  In 1962, the first red LED was developed, but the yellow LED did not appear until 1972.  High-intensity blue LEDs were not available commercially until 1989.  Some LEDs today use a junction which emits blue or ultraviolet to excite a phosphor which emits visible light of the desired colour.

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  3. Linear feedback shift registers (LFSR) have a multiplicity of applications besides making tunes. I use a maximal length LFSR to make a pseudorandom binary sequence to make a continuous laser act like a pulsed laser. It’s a sneaky way of turning a flashlight into a strobe. No LEDs involved, not even simulated ones.

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  4. drlorentz:
    Linear feedback shift registers (LFSR) have a multiplicity of applications besides making tunes.

    A curious application of LFSRs I stumbled across was in the early days of mobile phones.  Even with analogue technology, in order to conserve bandwidth and battery power, they were mostly half-duplex in the sense that they didn’t send silence over the network.  But subscribers would interpret total silence as “dead air” and think the connection had dropped.  So they used a little LFSR (I don’t know how many bits—it wouldn’t have taken many) as a white noise generator in the handset so that when it wasn’t receiving audio from the other end it would emit a faint hiss like customers were used to hearing on analogue dial-up circuits.  I think they still use synthesised white noise for this on GSM and digital land lines, but they probably have a more sophisticated way of generating it.

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