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Controlling Resistance With a Signal.

Discussion in 'General Electronics Discussion' started by Ghost Karate, Feb 11, 2013.

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  1. Ghost Karate

    Ghost Karate

    3
    0
    Feb 11, 2013
    Hi I'm new to the forum and quite new to electronics. I thought I would do the introduction and first question in one place.

    I'm studying a level 2 engineering course at college and have been chosen to represent my college in a electronics competition so I might be around asking a lot of stupid questions.

    I'm finding it hard because as it's only a Level 2 course we only get taught to a basic understanding.

    I'm working on my project and I was wondering if I can control a resistance value with a signal generated by a oscillator?

    Using a micro-controller is not a option.
     
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Lots of unknowns in your design, but a cheap hack if you don't need fine accuracy or resolution would be to take an LED and photosensor and put them face to face inside a piece of black heat shrink... Once sealed up use the oscillator signal to drive the LED, with some tweaking you can probably get a varying degree of resistance out as the varying oscillation levels might vary the brightness of the LED enough... This is just a cheap low level hack to do what you want that might or might not work in your design, the more details and the more information would likely yield better or other options...

    I would personally do it with a micro, but you said that was not an option, but we do have members that like doing things the old way so maybe they will offer up some direction :)
     
  3. Ghost Karate

    Ghost Karate

    3
    0
    Feb 11, 2013
    I should have put more info in the first post...

    Fine accuracy is very important.
    I'm trying to build a audio synthesizer that can be controlled by a MIDI key-bored. I'm going to use a MIDI to CV/Gate converter so I have voltages to work with.

    I have some of the design and there are lots of parts that use variable resistors to manipulate the sounds being generated in some way. I would like to modulate those resistors with with some of the signals I'm generating.

    For example....

    I have a audio signal going into a variable low pass filter and the cutoff frequency of that filter is controlled by a Potentiometer. I want to use the out put of a LFO to control the resistance giving me a filter sweep and for lack of a better word "WUB WUB WUB" sounds :p . I also want to still use the potentiometer in the filter as I would normally.

    They uses to make stuff like this a good 30 years before the silicone chip.

    If I can get this last part worked out I will have the basic design and will be able to move on to testing.
     
  4. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Yeah they made analog effects before the silicon chip, but you are going a little beyond that trying to interface and control the effect from a digital standard...

    There are still a ton of details that need to be considered before I would even hazard a guess at a viable solution...
     
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    There are other means to control a filter or an amplifier by a control voltage. Google
    • voltage controlled filter
    • voltage controlled amplifier
    to find a bunch of solutions from diskrete to integrated.
     
  6. Ghost Karate

    Ghost Karate

    3
    0
    Feb 11, 2013
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