I need help designing a resistor sequencer.

Discussion in 'Digital Circuit Design' started by elframbo, Aug 20, 2016.

  1. elframbo

    Thread Starter New Member

    Aug 20, 2016
    3
    0
    Hello,

    I'm new to electronics and have started modding guitar effects pedals. I
    need help designing a circuit that will sequence out three resistors. The pedal has a specific resistor that controls gain potential in the circuit.

    I did join the modding community forum as well and someone was nice enough to give me this design.

    http://i174.photobucket.com/albums/w114/quackzed/resistor sequencer_zpsivld4dme.png

    This circuit will be allowing the three resistors from the 4066 chip to switch in and out of the circuit at a controlable rate. I tried to build this on breadboard and used LEDs in place of the resistors R1,2, and 3 that were leading out of the 4066 chip. It did not work and I'm not sure if it was because of using the LEDs or if thee was an issue with the breadboard, a component, or if the design is not a working one.

    This lead me to look at LED sequencers, which have a very simple design, but I'm not sure how to connect those into my pedal's existing circuit. And I'm not sure it would even work properly because instead of LEDs I would use resistors.

    To sum up, the effects pedal has an option to mod out resistor R10 in the pedals existing circuit. I will be removing R10 and would like to replace it with a circuit that will automatically vary the resistance across the point where R10 used to be at a controlable rate.

    I hope this makes sense, as I said I am new to this. Any help is much appreciated.
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,173
    397
    The success of using a 4066 to switch resistors depends some what on resistor values. If I remember correctly,
    the contact resistance is around 160 ohms so if using multi k resistors there should be no problem. I am currently using a 4066 to switch 3- 10 k pots to control a 555 used as a servo driver. Your circuit looks good.
     
  3. elframbo

    Thread Starter New Member

    Aug 20, 2016
    3
    0
    Thanks for the reply. I tried that circuit and put LEDs where the resistors leading out from the chip should have been as a test to see if the LEDS would light up and they did not. My thoughts were that if the circuit is successful then the LEDS should have lit. Am I wrong in thinking that? Also I just purchased the breadboard and it doesn't feel like it is a quality piece of equipment. So I might need to test the breadboard as well. I purchased the components listed in the schematic and a breadboard to test building it.

    So if the LEDs do not work in this set up, then should I set it up again, and put the resistors there as they should be leading from the chip and test resistance across it?

    Thanks!
     
  4. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    What you need to do is put the LED's in place of the pots, with the cathode(shorter lead) to the junction of all the LED's, then connect that junction to ground. Connect a resistor from about 470 ohms to 1k ohm to the wire going to pins 2,4 & 9 of the 4066, and connect the other end of the resistor to +9V. The LED's need voltage to illuminate.
     
  5. elframbo

    Thread Starter New Member

    Aug 20, 2016
    3
    0
    Hey K7elp60,

    Thanks for the reply man. I'm sorry I'm a bit confused because I'm not very familiar with circuitry yet. I only have one pot in the circuit from my understanding and that is the variable resistor. What I'm taking away from your post is that I need to put the short lead of leds to the junction/terminal that connects to the pins 2, 4,& 9 of the 4066, then connect a resistor with a value of between 470 Ohms to 1k ohm to the 9v supply to test the circuit?

    Again sorry for my lack of understanding on this, I'm new to it and learning.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    You shouldn't expect them to. The CD4066 used in that circuit doesn't power the resistors/LEDs.
     
  7. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    This is the circuit, you could put 3 LED's in and you would see them all work
    4066 ckt.png
     
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