# 555 timer tone generator ???

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

1. ### twilightzonepinballGuest

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
knowledge.

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?

-Tom

2. ### D from BCGuest

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

3. ### colinGuest

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

Colin =^.^=

4. ### Bob EldGuest

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. ### twilightzonepinballGuest

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. ### Michael BlackGuest

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

7. ### twilightzonepinballGuest

I can interpret, just wanted a little clarification.

Peace.

8. ### Anthony FremontGuest

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 BCGuest

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

10. ### Jim ThompsonGuest

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

...Jim Thompson

11. ### twilightzonepinballGuest

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

12. ### Anthony FremontGuest

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 BCGuest

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

14. ### colinGuest

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. ### twilightzonepinballGuest

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

Thanks,

-Tom

16. ### MooseFETGuest

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 GriseGuest

[crossposted: sci.electronics.design,sci.electronics.basics,
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!
Rich

18. ### Rich GriseGuest

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

19. ### Don LancasterGuest

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