Advices for curcuit design of a 4017-based sequencer

Discussion in 'Digital Circuit Design' started by Harbasan, Jul 23, 2016.

  1. Harbasan

    Thread Starter New Member

    Jul 23, 2016
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    Hello everyone, i'm new here and i don't realy know if this is the right place to post this, but still, here it is.
    I've been working on a 8(4)-step sequencer based on two 555 and one 4017 IC, and i've ran into a problem. The idea is that on every step of 4017 IC, the second 555 (so called "sound generator") produces a different sound, which is manualy adjusted by 8 potentiometers, attached on each output pin of 4017. The problem is that i don't know how to design the actual connection between those 8 outputs in a way that would create 8 adjustable and independent sounds. I've experimented with basic NPN transistors and few additional resistors, but without any major success.
    Any advice is highly appreciated.
     
  2. #12

    Expert

    Nov 30, 2010
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    Try using pin 5 as a frequency modulator by inflicting different voltages on it.
     
  3. DickCappels

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    Aug 21, 2008
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    Sinus23 and #12 like this.
  4. #12

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    I wonder if the CMOS 555 has the 5K resistor string inside it. I don't think so because its idle current is 1/4 ma. In this case I think it is important to specify the LM555.
    The drawing in post #1 seems to show LEDs in the diode positions. Bad idea. Use regular diodes so you don't have to be concerned with reverse breakdown of the LEDs at about 5 volts. Besides, the 4017 chip can only do about 1ma and that's not going to get much light out of an LED.
     
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  5. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    I tested some for my brother doing quite well with just 950 uA.
     
  6. DickCappels

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    The National Semiconductor (now TI) LMC555 has a string of 100k resistors in place of the 5k resistors.
     
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  7. Sinus23

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    Sep 7, 2013
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    I did a "remix" of the Music box that Dick posted about 2 months ago(again). What I did was like he suggested putting potentiometers instead of the fixed resistors linked to the output of the 4017. I also used a pot for the 33k resistor on the 555 on the left to being able to control the speed. Another thing I did was changing the 10nF cap on the right side 555 to 1uF(IIRC could have been 0.1uF) because it sounds way better as a bass synth than the alternative...

    Then I made a simple bandpass filter that I could control the lower and upper limit of the filtering. Then I blocked the DC with an capacitor and put a 1k pot in series to attenuate just in case. Finally I connected the output to my 24Ohm expendable earplugs. Do not have them on when you turn the circuit on!!!

    It works pretty well. Got this fresh analog sound that after mainly dealing with digital synthesizers or listening to records that have been converted to digital you don't hear often straight from the cow:cool:

    One thing I did is what #12 adviced against which is putting LEDs in series with the output of the 4017. Although they got lit if the resistance wasn't too much the voltage drop limited the range of notes it would play...So I removed them.

    Just my 2cents. Happy experimenting;)

    Oh I almost forgot. The original schematic has 2 fixed notes so its 10 steps. You're going to have to make the 4017 reset after output 7(the eighth step).
     
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  8. #12

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    In the case of the CMOS-555 with 100k resistors inside it, the maximum current required to shift the voltage at pin 5 is below 200 ua. There lies my concern that LEDs will not be of much use unless you add a resistor to ground to increase current from the 4017 chip, and there isn't much to work with considering the 4017 is rated at about 1 ma to 2 ma depending on the power supply voltage.

    So, thanks to the cat lover (@Sinus23 )for doing the experiment to find out if the LEDs help or hurt.;)
     
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  9. Sinus23

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    Sep 7, 2013
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    Well almost every mission needs a man on the ground. It just so happened that I had done something similar about 2 months ago.

    But you knew that beforehand. I only had my suspicions before I actually tried it out ;)
     
  10. #12

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    Yep. Some of my best advice here comes from mistakes...uh...circuits I have actually built.:p
     
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  11. hp1729

    Well-Known Member

    Nov 23, 2015
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    Design 796 music.PNG
    If using the control voltage pin doesn't give enough variation here is a more complicated option.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    When the npn bjt turn off and the Vb of pnp bjt will be floating, you can improve it using two methods, the one is adding a Rc1 or Q2_Rbe, the situation is similar as pnp and npn, please check those two circuits as below on the right side.

    [​IMG]

    The Transistor's Sink And Source.
     
  13. hp1729

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    Nov 23, 2015
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    Good point. I was hasty in my post. I know better.
     
  14. hp1729

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    Design 796 music.PNG Corrected drawing.
     
  15. AnalogKid

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    One problem with almost all 555 circuits for individual tone generation is that the 555 output is not symmetrical. Often, varying one resistor changes only one half of the output waveform, so what you get as you go from one note to another sounds more like 2-note chords where one note is changing and one note is fixed. This is in addition to the sound distortion that comes from dealing with square waves. You can get around this by adding a divide-by-2 flipflop (1/2 of a CD4013) to the 555 output. Now, no matter how far off the duty cycle is, the output will be a symmetrical square wave that stays 50/50 as the resistors change the notes. Unfortunately, now the big fat 555 output stage is not driving the speaker, so you will need some form of speaker driver.

    Another way to get there with fewer parts is to use a 555 circuit that gives a symmetrical output. This is done with a single timing resistor from the output to pins 2 and 6 and no connection to pin 7. Unfortunately, now neither end of the resistor you want to vary is tied to a constant DC potential, so a simple 4017+diodes circuit will not work.

    But for fewer parts and fewer soldered pins, you can use a binary counter like a 4024 driving an 8-channel analog multiplexer like a 4051. Using a 4060 instead of a 4024 eliminates one 555.

    555 > 4017 > 8 diodes > 8 variable resistors > 555 > 4013 > speaker driver > output

    or

    4060 > 4051 > 8 variable resistors > 555 > output

    ak
     
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  16. ScottWang

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    Aug 23, 2012
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    @AnalogKid:
    Using the CD4013 to get 50%/50% duty cycle is good method, I was used it for 1Hz.

    [​IMG]

    Using the cmos 555 and the circuit as Dick attached in #3 then it can be get a 50%/50% duty cycle, or just using the NE555 and the circuit as below that it also can be reach to the same goal, choosing the 1% or less for R1 and R2, and it can be using the fixed resistor to replace VR1.

    The circuit of NE555 50% duty cycle.

    [​IMG]

    The circuits were linked from ScottWang's blog.
     
  17. AnalogKid

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    Something like this. The 4060 timing components are selected for 1.5 seconds per tone, about the same as in post #1. Note - components are what's in my design library. Use a CD4051 for 9 V operation, add decoupling capacitors, etc.

    oops - ground on U3 pin 5 is incorrect. See corrected schematic in next post.

    ak
     
    Last edited: Aug 2, 2016
  18. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Corrected schematic.

    Note no capacitor on 555 pin5. I've done lots of 555 circuits with and without it, and never have seen it make a difference or been able to force enough noise into the chip to be able to see a difference. Of course, feel free to add one per the datasheet.

    ak
    ToneSequencer-2-c.gif
     
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  19. hp1729

    Well-Known Member

    Nov 23, 2015
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    Interesting, but is it always making a hum of some kind? No "off"?
     
  20. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The circuit in post #1 runs continuously.

    ak
     
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