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Analog Circuit to Randomly Modulate Amplitude and Frequency

Discussion in 'General Electronics Discussion' started by epsolutions, Sep 7, 2019.

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  1. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    I doubt you will find an ic that works at such low frequencies. Usually these mixers are for high frequency applications. I wonder if someone comes up with a suitable chip.
  2. darren adcock

    darren adcock

    Sep 26, 2016
    I'm not following this thread completely, but, I use a two Yusynth modules in my anologue modular synth system to create pseudo random modulation. The module has a random cv output, a sample rate clock in and built in noise sources. This module, it's circuitry is easy enough to breadboard and test,

    Linked to the yusynth quadrator LFO,

    Can all go to a mixer

    But as said i'm not completely following this thread so it might not be appropriate.
    Harald Kapp likes this.
  3. epsolutions


    Sep 7, 2019
    Thank you. Those are both interesting circuits. The random LF noise source is certainly relevant to this thread. The quad LFO would make a great signal source for a rotational effect.

    To complete my project, I am hoping someone can suggest an IQ mixer IC that will operate at low frequency. Or an alternative solution using other components that do not involve programming.
  4. Alec_t


    Jul 7, 2015
    :confused: If it has to be replicable then how can the modulation be random?
    davenn likes this.
  5. epsolutions


    Sep 7, 2019
    The depth of random modulation, relative levels of signals prior to mixing, etc.
  6. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Laboratory experiments relating to plant growth? If this were really a laboratory experiment instead of some fanciful pipe dream, you would realize that well-designed scientific laboratory experiments are always deterministic: to be a valid laboratory experiment that follows the "scientific method" requires that others "competent in the art" be able to duplicate the experiment and verify the results. To see how this works in the real world, Google "fleischmann and pons cold fusion" and find out what effect early publication had on the reputation and careers of these two chemists, who initially announced their "results" of a "laboratory experiment" that allegedly demonstrated cold fusion, generating more heat output from their experimental setup than the electrical energy input to the experiment.

    Upon hearing this good news, I rushed right out and built an inexpensive space-heater for small apartments that took advantage of the "over unity" conversion efficiency of a cold fusion heater, and the gullibility of early adopters, to make zillions of bux selling these cheap, money-saving, space heaters, featuring zirconium-coated ceramic heating elements and complete with Amish woodworker-made cabinets... NOT! It could be that Fleischmann and Pons did discover something, but to this day it is not at all clear exactly what they may have discovered or, more importantly, exactly how their discovery worked. That hasn't discouraged thousands of basement wannabe physicists from trying to duplicate and improve on the original cold fusion apparatus, but AFAIK no one is selling any product based on cold fusion.

    As for plant growth experiments? It is well known that depriving most plants of sufficient light will either stunt their growth or kill them. Providing too much light can also have detrimental effects, but these effects can be more subtle. AFAIK no one has studied what effect (if any) a modulated light source has on plant growth, so maybe this is a valid path to explore. Here in Florida there is a huge (and growing) commercial business revolving around medical marijuana, which is legal to use and possess with a doctor's prescription. The horticulture is well-developed and dozens of varieties and cultivars are available for purchase by the consumer. The growing conditions are also well-defined in terms of how much water, fertilizer, and light are required to harvest a crop in the shortest period of time.

    If you can define an experiment that shows how the "shortest period of time" can be significantly decreased, there is potentially a huge market that would employ your paradigm. Perhaps it could also be applied to other field crops, such as soy beans or corn, but I doubt it. In my opinion, only plants that produce large amounts of product in the smallest possible, artificially lighted, growing area are suitable candidates. Nevertheless, the study would be interesting if conducted properly.

    The weakest link I have seen so far is the lack of a precise definition of the randomness you seek. I seriously doubt you want to attempt to implement true randomness... for one thing, it is impossible to do so; for another thing, it is extremely difficult and expensive to even come close. However, there are statistical tools that can be used to measure randomness, and these same tools can be used to help you design "repeatable" randomness for your experiment, thereby rendering your experiment suitable for duplication and verification by "others skilled in the art." Of course you may want to keep everything secret, since it is potentially worth money, so perhaps repeatable randomness is not a requirement for you. But without repeatability, how will you determine the effects of particular random patterns of illumination? I suppose you could make videos and correlate these to plant growth, but that sounds like a lot more work than is necessary. Maybe you could find a stand of quaking aspen trees (they are common in Colorado) and on a bright and sunny day take videos of the ground illuminated by the sun through these trees on a breezy day. That would be pretty random. Good luck with your experiment.
    Harald Kapp likes this.
  7. epsolutions


    Sep 7, 2019
    Junction noise is sufficient randomness for my application. There are variables other than its frequency distribution that will be controlled.

    Yes, I know of someone who pointed a photocell at trees blowing in the wind to obtain a random signal. Lava lamps do the same. Noise can also be generated in audio editing software. But that is not what I am looking for.

    Based upon the responses so far, I plan on using the random noise block from the uploaded circuit below, in combination with an AD835. The following discussion suggests that mixer will work at low frequencies. https://electronics.stackexchange.c...requency-mixing-at-low-frequencies-with-ad835

    Attached Files:

  8. epsolutions


    Sep 7, 2019
    I built the part of the above circuit intended to produce a "random voltage". It all works fine until the low pass filter (U3d) which I assume is supposed to remove everything above about 30Hz and leave a slow random wave form. However, the output still looks very like pink noise.

    Can anyone please explain why this might be happening?
  9. AnalogKid


    Jun 10, 2015
    As above, there a re several ways to amplitude modulate "any" signal, from a simple FET acting as a voltage-controlled resistor to a four-quadrant multiplier. And there are several ways to produce amplitude-limited and bandwidth-limited random voltages. But ...

    Varying the frequency of "any" signal, while (presumably) maintaining its (unknown) wave shape is very difficult. OK, very very. Wait, I left out a few verys. Absolutely, positively *not* impossible, but ...

  10. bertus


    Nov 8, 2019
  11. epsolutions


    Sep 7, 2019
    That is a great source of circuits Bertus, and there is a ring modulator that uses the AD633.

    But the problem I am still having is not the modulation (multiplier). It is how to generate, or extract from noise, an extreme low frequency, random wave form. That goes in the X input of an AD633 while the signal to be randomly modulated goes in the Y. The latter happens to be a continuous sine wave.

    Given that the preferred modulation is random, I am not trying to preserve any particular waveform. Quite the opposite in fact. I want to randomly change channel Y's amplitude and phase (frequency). Please review my OP and accompanying image.

    So the remaining question is "how to generate a slow random wave with analog circuitry". Think white noise but with all frequencies above about 30Hz removed. I thought the synth circuit attached above was designed to do this, but I cannot get it to work. As stated, the LP filter has little or no effect.

    Can anyone identify the exact problem? A better choice of filter?
  12. darren adcock

    darren adcock

    Sep 26, 2016
    I can't answer your question. And possibly only distract from your endeavors. It's been on my mind that maybe some of Ian Fritz chaos circuits might offer some assistance. I've not built anything of his yet but I know others that really like his circuits. I understand chaos isn't the same as random. But thought I'd share in case it holds some relevance.
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