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What do the pots do in this circuit?

  1. Jul 8, 2011 #1
    This is a circuit diagram of a 4-step sequencer connected to an atari punk console. What I want to know is what those pots connected between the 4017 chip and the diodes do. I know they control what voltage appears at the terminal connected to pin 2 of the 556, but that pin 2 is the threshhold pin that only responds to two different voltage levels, high and low, so surely the pots do nothing and one only really needs the switches?

    Here is the schematic: http://note.monoanimal.com/images/apccircuit_2.jpg [Broken]

    Sorry for the quality.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jul 8, 2011 #2
    I think you are right. (I am thinking only in terms of ' output from 4017 being selectively applied to trigger pin of 556' I don't know what the rest of the circuit do)
     
  4. Jul 8, 2011 #3
    The pots set the voltage level for pin 2 of the 556. The diode drop is more or less constant so you can adjust what two voltages are sent to the 556 by adjusting the voltage on the anodes of the diodes with the pots. They are an important part of the circuit if you need to do any kind of level shifting between the 4017 and the 556.
     
  5. Jul 8, 2011 #4
    I don't understand how the pots have any more affect that the switches do, unless the pots allow slightly greater control as to how fast you want the comparator to trigger. Does that sound right?
     
  6. Jul 8, 2011 #5
    The switches don't adjust the voltage levels, they just allow whatever it happens to be to go through. The pots allow you to adjust the voltage level (e.g. 1V or 4V or whatever).

    So, the pots allow you to set the threshold where you want the comparator to trigger.
     
  7. Jul 8, 2011 #6
    From what I can tell from the wikipedia article, the comparator switches when the voltage at threshold (pin 2) is greater than the voltage at control (pin 3). The voltage at control is set at 2/3 Vs, so if Vs is 5, what difference does it make if the voltage at pin 2 is set at 1V or 2V by the pot? The comparator only switches at 3.3V so what use does being able to vary the voltage from 0-3.3V have if the 555 will be in the same state in that entire range?
     
    Last edited: Jul 8, 2011
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