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Super small electronic variable resistor -- Exists?

  1. Oct 22, 2016 #1
    Hi I couldnt find of these exist anywhere.
    Is there a component that is a variable resistor that adjusts based solely on receiving an up/down signal? And maintains its state on powerdown? I dont want this solution to involve any type of software, just a hardware solution. Looking for something that will work in the 8hz frequency less than 12v and 100mA
    I couldnt find anything.
  2. jcsd
  3. Oct 22, 2016 #2


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    welcome to PF

    Resistors don't do that without a lot of other surrounding components/circuitry
    so what are you really trying to achieve ?

  4. Oct 22, 2016 #3
    Essentially I am trying to create a simple neural network using only electronics on a circuit board. This variable resistor I am talking about would act as a weight. And the next resistor in the line, whether it fires or not would represent the neuron
  5. Oct 22, 2016 #4
    Just googled analog neural network circuit, dont know why I didnt do that before. Yes thats what I want to create. From what I am reading technology seems to be limiting in terms of precision variable resistors or amplifiers that can maintain their state in the off position.
  6. Oct 22, 2016 #5


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    I think you had better do some reading on resistors and what they are and other basic electronics :smile:

    resistors don't do the things you are implying

  7. Oct 22, 2016 #6
    I thought I had... okay let me try to explain better what I want to do logically
    I want an input to be adjusted either up or down then into fed into a gate which has an activation potential, so that over a threshhold current it will pass through, and under it will not pass through.

    Further more, the component which amplifies or reduces the signal needs to be adjusted by the circuit itself, so the circuit needs to have some sort of feedback loop to the "adjuster".
  8. Oct 22, 2016 #7
    There is only one thing that I can think of which will do what you want. Take a look at the memristor. Unfortunately it's cutting edge stuff that isn't available yet.
  9. Oct 22, 2016 #8
    Yea thats basically exactly what I am looking for. Unfortunate that its only experimental at the moment. I wonder if there is any suitable macroscopic equivalent, its response speed isnt super important, for example water with salt in it, the salt could be electrically removed to increase resistivity, obviously water and electronics is a terrible idea, but the first one that came to mind.
  10. Oct 22, 2016 #9


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    I know of no such device.

    But you could use an external laser to ablate away material, making resistance higher. An external ion gun could deposit material, making resistance lower. If those external guns could be aimed, they could adjust a large array of resistors. It would take LOTS of engineering to make that work in real life.

    If you always start with a virgin array, then only ablation is needed, skipping deposition.
  11. Oct 22, 2016 #10
    I like the idea, ofcourse like you said it would be difficult, too difficult of course, but these work around ideas are very welcome.
  12. Oct 22, 2016 #11
    Out of curiosity, why do you not want to create a digital design? You could even do this completely with software in a general purpose computer.
  13. Oct 22, 2016 #12
    Because the computations performed by a processor to train a neural network are prohibitive. I believe its possible to design an analog neural network that can out perform a digital representation. Ofcourse if I can build it all, my first version won't out perform anything, but maybe after I build it, I can build it again, faster, with smaller components. Kind of like how vacuum tubes advanced.
    Also I have an invention idea whoch requires a neural network that can be trained very fast, and very responsive.
  14. Oct 22, 2016 #13
    It sounds like you have an interesting problem. I'd like to help but I'm afraid I don't know anything about neural networks. I do know a thing or two about digital design. It is possible that something exists which you can buy off the shelf and use.

    When someone says "computationally prohibitive" I start thinking about FPGA's. Have you considered using FPGA's? The Xilinx Zynq-7100 has about 2000 DSP blocks. With a realistic clock speed of 300MHz that means you could configure the chip to perform 600,000,000,000 multiply-add operations per second. Is that enough?
  15. Oct 22, 2016 #14
    Im sure that would work for what I want to do, but if I am relying on a classical processor I can never hope to compete with companies like google and their AI efforts.
    In addition to the vast computational resources they have they also have mathmaticians working out complex algorithms to make those virtual nets learn.

    I want to approach neural nets from a new perspective. I think an analog model can outperform a digital one. Consider this, a standar computers memory can only be a 1 or 0. If you think of the amplifiers setting as memory(which in terms of neural nets thats what it is) then the value can be 0, 1 or anything in between this is where the analog version makes its gains over the digital version which has to simulate these values with floating point variables.
    The question is can I build it, and with how much complexity.

    But as you suggested I could already create my invention using the already available technology, that is tempting and Ill have to give that some thought.
    Thanls for your feed back.
    Last edited: Oct 22, 2016
  16. Oct 22, 2016 #15

    jim hardy

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  17. Oct 22, 2016 #16
    I've used digital pots in a number of designs, real handy devices. Availability is fairly wide on them. The volatile type are probably more common, but there are non-volatile ones available that remember the last setting on power up. Some provide a one wire up/down interface, but an SPI or I2C interface is most common. You can find them in very small SMD packages.

    BTW, Microchip has a wide range available. Maxim makes a 1024 tap pot which can be handy if you need higher resolution. Most are 256 tap and less commonly 512 tap. That indicates how many steps they have.
    Last edited: Oct 22, 2016
  18. Oct 22, 2016 #17


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    There's nothing wrong with that, although I suspect that it has been done before. However, you could implement the neural network with something analog, but do the learning with something digital, or do learning all software. The final neural weights, once learned, could be burned into an analog network.

    You could even take an existing neural network (I think of Google's speech recognition network; the result of massive deep learning.) and have it burned into an analog network. Then see how much better the analog one performs. That would be a reasonable way to investigate the value of your ideas.
  19. Oct 22, 2016 #18


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    The closest I can think of that is analog and 'holds' would be a sample and hold circuit. It of course not a resistance but a voltage. Power down would also be a compromise here. If you want to get really crude a motor driving a potentiometer technically fits your requirement if you are liberal about defining super small.
  20. Oct 23, 2016 #19


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  21. Oct 23, 2016 #20


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    Hi MeaningfromForm.
    Maybe if you gave us the block diagram of the network you want to make, we might find a way to do it with much lower power and a lower voltage supply for the analogue circuits and pots. Some of us are good at mapping functionality to available analogue circuits.
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