Tone sequencer

Discussion in 'General Electronics Chat' started by TheBellows, Nov 25, 2009.

  1. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Hi,

    I've built this tone sequencer and it works in a way, but not the way i was hoping.
    Instead of cycling through 8 tones in 8 steps it repeats two of the tones twice in the first 4 steps followed by the last 6 tones which makes a total of 10 steps.
    Isn't it supposed to cycle 8 tones in 8 steps?
    I've tried to rearrange the leads that goes from the Dual BCD Up-Counter (i use CD4518BE) to the Multiplexer (i use 74HC4051N) and i get different patterns, but not the linear 8-step pattern i want.

    Do i use the right chips? Is the circuit correct? Any ideas?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Double-check your wiring.

    The schematic looks right.

    The odd part about the way it was drawn is that it will play the frequency set by R9 first, then R8, R7 ... to R2, and then repeat - so it's backwards from what you might expect.
     
  3. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    I've checked the wiring over and over, it should be correct. Doesn't seem like there is something wrong with my breadboard either.

    I said "it repeats two of the tones twice in the first 4 steps followed by the last 6 tones which makes a total of 10 steps.", is not correct,
    the sequence goes like this: R9-R8-R7-R6-R5-R4-R3-R2-R9-R8.
    I want to get rid of the last two steps.

    Here is a short audio sample: http://www.archive.org/details/Sequence_471

    Is it possible that one of the chips are faulty? I have no spares or else i would try...
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    OK, a few important things that are not shown on Forrest Mims III's schematic are bypass capacitors.

    On each IC, you should have a 0.1uF capacitor (ceramic, poly, metalized film, etc) across the Vdd/Vss or Vdd/ground pins.

    Without those capacitors, you might be getting "hiccups" in the counts on the 4518 due to spikes on the voltage supply.
     
  5. ifixit

    Distinguished Member

    Nov 20, 2008
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    In your case you should use the 4520, a dual binary counter. The BCD counter will make counts 8 & 9 look like counts 0 & 1 unless you reset the counter (pin 7) at the "8" count.

    Wiring pin 6(Q4) to pin 7(reset) may do the trick.

    Good Luck
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You're exactly right! Boy, did I blow that one! :rolleyes:

    BTW, make sure that you disconnect pin 7 from ground before you connect it to pin 6.
     
  7. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Now i placed a ceramic 0,1uF cap from vcc to ground on all three IC's, but all it did was slowing down the sequence...
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    "Ifixit" posted the solution.

    Disconnect pin 7 of the 4518 from ground.
    Jumper pin 7 of the 4518 to pin 6.

    Problem solved.

    By the way, on just about ANY IC, you want to have a 0.1uF capacitor across the supply pins.

    If you have a split supply (like with opamps, Vcc/Vee/Ground) then you want a 0.1uF capacitor between both power supply inputs and ground.
     
  9. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Aha, that does the trick indeed.

    Thank you! :)
     
  10. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    I didn't know that. Thank you! :)
     
  11. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    Another question: Should i use an output capacitor, there are none in the schematics,
    but i have placed a 0,47uF poly cap as an output cap and 100KB pot between signal, output and ground as a volume control.
    Is this ok?
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Sure, you can do that.
    Just be certain that you don't reduce the pot below about 270 Ohms. Use a fixed 270 Ohm resistor between the pot and the speaker just to make sure it doesn't happen.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    A capacitor from the output to ground is simply a short circuit at high frequencies. If there are high frequencies then it might cause the current to be too high and blow up something.
     
  14. TheBellows

    Thread Starter Active Member

    Jan 18, 2009
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    0
    I did exactly as the schematics, but after the 270ohm resistor i placed the capacitor because i thought there should always be an output cap?
    I placed the volume control after the cap...i really don't know what i'm doing, so i'm glad i have you guys. :p
     
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