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555 timer tone generator ???

Discussion in 'Electronic Design' started by twilightzonepinball, Apr 2, 2007.

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  1. Hello,

    My name is Tom and I am new to this group. Please forgive my
    newbieness. I am an Industrial controls tech with limited electronics

    I was hoping I could get some help designing a simple tone generator
    for a unique application. I have so far built a simple tone generator
    using a 555 timer chip and some resistors and caps with a circuit I
    found online. I am using pin 5 to control it as a VCO astable.
    Everything works great, the input dc voltage is varying the tone, but
    I want the frequency to go up with voltage. Kind of like an audio
    voltage monitor. This input voltage is about 0-14 volts. The problem
    is that the frequency goes down when the voltage goes up. Just the
    opposite of what I need.

    Can anyone suggest a solution?

    Thanks in ad advance,

  2. D from BC

    D from BC Guest

    Perhaps use a linear inverting buffer amp..
    Can be a transistor cct or op amp cct.
    D from BC
  3. colin

    colin Guest

    You could apply the 0-14v to an additional resistor wich charges up the

    Colin =^.^=
  4. Bob Eld

    Bob Eld Guest

    Use an inverting opamp as mentioned above. Set the gain less than one so the
    0 to 14 volt input translates to the pin five voltage range, approxamately
    1/3Vcc to 2/3Vcc. Be sure the 555 oscillates properly through the whole
    range. Add an offset resistor to the input of the op amp to pull the 0 Volt
    input to the maximum pin 5 value (lowest frequency). The resistor should go
    between the neg input of the op amp to a minus voltage (-15 volts). It can
    also be done with all positive voltages with a little thought.
  5. Thanks guys for the help. Being an electronics NOOB I only partially
    understand the suggestions. Could anyone explain in layman's terms how
    to connect these components (op amp)?

    -Tom - tomwible at verizon dot net
  6. Here's a clue. YOu ask in sci.electronics.basics where beginners questions
    below, and then you might get some answers.

    YOu aren't designing, you don't have the background or knowledge to design.
    YOu can't even interpret the responses you've gotten, which in part is
    the fault of you asking in a newsgroup intended for matters relating
    to the design of electronic equipment.

  7. I can interpret, just wanted a little clarification.

  8. Here's a clue for YOu Michael, YOu don't have to be such an arrogant ass.
    We get enough of that around here as it is. What exactly gives you the
    right to tell anyone where to post or to summarily judge their capabilities?
    Got clue yet?
  9. D from BC

    D from BC Guest

    The op amp cct is the classic "inverting amp" configuration and can be
    found in certain basic electronics books and sometimes on op amp
    D from BC
  10. Jim Thompson

    Jim Thompson Guest

    What has Michael Black himself done to earn "designer" status ?:)

    ...Jim Thompson
  11. I did some googling on inverting op amps and learned a lot. I am not
    sure how to find the chip I need, or how to set it up to give me only
    positive voltages to the 555. How can I get 0 volts to the 555 with a
    14 volt input to the op and then 14 volts with 0? The op will give me
    negative voltages right?

  12. I don't know, but most of the posts I see from him seem to be along these
    lines. AFAIC, once the OP decided that he wanted the circuit to work
    differently, he became a "designer". ;-)
  13. D from BC

    D from BC Guest

    On 2 Apr 2007 17:16:35 -0700, "twilightzonepinball" <>
    Nahh..nahh...nahhh...don't call it negative voltages...
    (Maybe negative transfer slope.)
    The op amp is to work in single rail mode.
    The entire circuit runs off a single rail. There are no negative
    voltage sources.. (AFAIK)
    You will only get voltage inversion from the op amp. Increasing input
    voltage results in a decreasing output voltage.
    The resistive network around the op amp must be designed such that you
    get your control limits to the 555VCO.
    D from BC
  14. colin

    colin Guest

    do you realy want to do it with an op amp ?
    It would be so much simpler just to control the frequency by the current
    charging the capacitor,
    just needs a resistor from the control voltage to pin 7, instead of pin 5.

    Colin =^.^=
  15. Yes someone on the basic forum mentioned that and I plan to try it.


  16. MooseFET

    MooseFET Guest

    I think this will help you to work things out for your self. When you
    are done, you will have learned a lot more about op-amps.

    Start with this very simple mental model of a rail to rail op-amp:

    An op amp has two power supply connection, a +In, a -In and an
    Output. This is how I will refer to the pins.

    The workings of an op-amp can't ever take the Output beyond the supply
    voltage no matter how hard it tries. If the (-) power connection is
    hooked to -3V, the Output can't go below -3V.

    An op-amp only will function if both both of its inputs (+In and -In)
    are at a voltage somewhere between the two supply voltages.

    No current ever flows in our out of the +in or -In pins. If a
    resistor brings current to that node of the circuit, some other
    resistor must be taking it away.

    The output of an op-amp is controlled by the difference in the inputs
    voltage. If the +In is more positive than the -In, the output swings
    upwards very rapidly. If the -In is more positive, the output swings
    down rapidly.

    Now remember that you can make voltage dividers out of pairs of
    resistors and stuff like that and see if you can work out how to make
    the circuit with this simple op-amp model.
  17. Rich Grise

    Rich Grise Guest

    followups-to sci.electronics.basics]

    Well, these aren't "Forums" - these are USENET newsgroups.

    This whole discussion belongs in sci.electronics.basics, and I've set
    followups-to to move the whole thread, if possible. The people who
    frequent s.e.basics are much more amenable to beginner-style questions.

    Good Luck!
  18. Rich Grise

    Rich Grise Guest

    I was going to give Micheal a demerit for harshness, but I do opine that
    beginners "should be" gently guided to the .basics NG, where there's a lot
    less harshness in general, and a lot more willingness to answer newbie

  19. Use a PIC, of course.

    555 timers have been utterly and totally useless for two decades now.

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  20. And there you have it everyone. You should revamp/amend your awesome book
    line-up with a complete set of PIC cookbooks. I would really enjoy a "PIC
    Active Filter Cookbook". ;-)
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