555 timer tone generator ???

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

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

Colin =^.^=

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.

text -

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

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.

Michael

I can interpret, just wanted a little clarification.

Peace.

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?

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

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

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
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         America: Land of the Free, Because of the Brave

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?

-Tom

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". ;-)

On 2 Apr 2007 17:16:35 -0700, "twilightzonepinball" wrote: [snip]

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

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 =^.^=

messagenews: snipped-for-privacy@4ax.com...

Yes someone on the basic forum mentioned that and I plan to try it.

Thanks,

-Tom

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.

messagenews: snipped-for-privacy@4ax.com...

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! Rich

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 questions.

Thanks, Rich

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
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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". ;-)