Tank circuit questions

[WM Morgan]

in re tank circuits, from a non-technician/non-electrician:

What's the slowest (or lowest frequency) oscillation that is practical
or do-able with a tank circuit?

How does a tank circuit behave with a constant d.c. power supply? (The
examples I'm finding describe a momentary feed of current.)

With a tank circuit or not, what's the simplest circuit possible that
can oscillate continously at 1/3 to 1/6 Hz, with, say, 12V d.c.?

Can the same method be used with your standard household a.c. current?
If not, what would accomplish the same with household a.c.?

 

[Paul Burridge]

in re tank circuits, from a non-technician/non-electrician:

What's the slowest (or lowest frequency) oscillation that is practical
or do-able with a tank circuit?

How does a tank circuit behave with a constant d.c. power supply? (The
examples I'm finding describe a momentary feed of current.)

With a tank circuit or not, what's the simplest circuit possible that
can oscillate continously at 1/3 to 1/6 Hz, with, say, 12V d.c.?

Sounds like a job for Jim's long tau circuit, if you don't mind a
triangle wave output. Does it have to be a sine?

 

[Jim Thompson]

Sounds like a job for Jim's long tau circuit, if you don't mind a
triangle wave output. Does it have to be a sine?

As in "Long Tau Sally" ?

I think my synthetic tanks (see the active filter stuff on my website)
will work at arbitrarily low frequencies except there may be problems
with capacitor dissipation factor.

...Jim Thompson

 

[John Popelish]

in re tank circuits, from a non-technician/non-electrician:

What's the slowest (or lowest frequency) oscillation that is practical
or do-able with a tank circuit?

Practical and do-able are not necessarily in the same category. What
is your budget (and land area) available? Got any liquid helium?

How does a tank circuit behave with a constant d.c. power supply? (The
examples I'm finding describe a momentary feed of current.)

This depends on the voltage rating of the cap or the current rating of
the inductor.

With a tank circuit or not, what's the simplest circuit possible that
can oscillate continously at 1/3 to 1/6 Hz, with, say, 12V d.c.?

RC oscillators that ramp the cap voltage back and forth between
specific voltage levels are the simplest. Take a look at the data
sheet for the LMC555 timer chip:
http://cache.national.com/ds/LM/LMC555.pdf

Can the same method be used with your standard household a.c. current?
If not, what would accomplish the same with household a.c.?

Probably not, but I still have no idea what you are trying to
accomplish.

 

[Jamie]

if your not worried about shape of the wave use a 555 Timer which
can be found at your local radio shaft with example data books on how
to make an osc..

 

[WM Morgan]

If not a sine wave, then a triangle wave would work.

A long tau? What is that?

Now, this "synthetic tank" thingie... went to your website and I poked
around but couldn't get a handle on anything I saw there.

Basically what I am trying to do, using a steady power supply, is to
make a small light bulb vary continuously and steadily in brightness,
from zero (or near-zero or dim output) to max brightness and back to
zero, over an interval of from anywhere from three to about six or
seven seconds.

And do it with the simplest circuit possible.

Some variability in the cycle is acceptable; it may in fact be
desirable.

 

[Adrian Jansen]

"Simplest" circuit can mean a lot of different things.

Assuming a small lamp, at low voltage.

If you want a circuit you can "understand" because its simple, then the
classic RC oscillator 2 opamp circuit generating a triangle wave will do
what you want with only a few resistors and caps, plus the one IC and a
transistor.

On the other hand if you want absolute lowest parts count, an 8 pin
processor with internal oscillator and PWM output would do the job with just
one transistor external - to drive the lamp. The program, while fairly
trivial, will not be "simple" in the sense that you need a lot of experience
to understand what you are doing to implement such a thing, and looking at
the finished result, or indeed a circuit, will give you no clue as to how
the thing operates.

--
Regards,

Adrian Jansen
J & K MicroSystems
Microcomputer solutions for industrial control

 

[Jim Thompson]

If not a sine wave, then a triangle wave would work.

Sounds like a DAC might be the best suited for your application.

A long tau? What is that?

Tau? Think Greek. Long time constant.

"Long Tau Sally" as in "Long Tall Sally" was a play on sounds-like, a
favorite rock-n-roll tune from us old guys era ;-)

Now, this "synthetic tank" thingie... went to your website and I poked
around but couldn't get a handle on anything I saw there.

See all the "Gyrator" topics on the S.E.D/Schematics page,

Basically what I am trying to do, using a steady power supply, is to
make a small light bulb vary continuously and steadily in brightness,
from zero (or near-zero or dim output) to max brightness and back to
zero, over an interval of from anywhere from three to about six or
seven seconds.

And do it with the simplest circuit possible.

Some variability in the cycle is acceptable; it may in fact be
desirable.

[snip]

I'd do it with a DAC and some counters.

...Jim Thompson

 

[Walter Harley]

Basically what I am trying to do, using a steady power supply, is to
make a small light bulb vary continuously and steadily in brightness,
from zero (or near-zero or dim output) to max brightness and back to
zero, over an interval of from anywhere from three to about six or
seven seconds.

Try it first with an adjustable power supply, by hand.

You will soon discover that the brightness of a light bulb is NOT linearly
related to the voltage across it, or even to the current through it. It's
actually a bit tricky to get a nice gradual ramp in brightness. As you ramp
up the voltage, the bulb stays off or very dim until a certain threshold, at
which it abruptly gets brighter.

After you've gotten a feel for what the relationship between voltage and
subjective brightness is, you might have an easier time getting this to
work.

Most of the time to control brightness of an AC-powered lamp people don't
vary the voltage; rather, they vary the duty cycle, using a triac or MOSFETs
to switch the voltage on and off mid-cycle. For max brightness the bulb is
switched on continuously, for min brightness it's only on for a small
fraction of each AC cycle. You can google for "triac dimmer circuit" or
some such to get more details.

If you're just talking about a flashlight bulb, you might have an easier
time than if you're talking about a 120VAC bulb. (I don't know what "small"
means to you.)

LED's have a pretty smooth relationship between subjective brightness and
the current being passed through them. They're a bit easier to control than
incandescent bulbs.

 

[John Woodgate]

I read in sci.electronics.design that WM Morgan <[email protected]>

Basically what I am trying to do, using a steady power supply, is to
make a small light bulb vary continuously and steadily in brightness,
from zero (or near-zero or dim output) to max brightness and back to
zero, over an interval of from anywhere from three to about six or seven
seconds.

OK, when you tell us *what you are trying to do*, we can tell you ways
to do it. The simplest way *for you* [1] of doing what you want is to
generate a triangular voltage waveform. You can do this with a 555 timer
chip and a comparator. You need a lot more information that just that,
but I just don't have time to design something for you. We need to know
the voltage and current or power of your 'small light bulb'.

[1] Someone with enough background and experience to design a solution
for themselves might use a microprocessor (PIC) or any one of a number
of techniques. The need here is to tell you a way of doing it that gives
you the highest probability of success.

 

[John Woodgate]

I read in sci.electronics.design that Jim Thompson

I'd do it with a DAC and some counters.

Yes, you would but you have 50+ years experience. The OP is clearly a
beginner, and needs a solution with a shallow learning-curve.

 

[John Woodgate]

I read in sci.electronics.design that Walter Harley

Try it first with an adjustable power supply, by hand.

You assume that the OP has an adjustable power supply. I doubt it.

You will soon discover that the brightness of a light bulb is NOT
linearly related to the voltage across it, or even to the current
through it. It's actually a bit tricky to get a nice gradual ramp in
brightness. As you ramp up the voltage, the bulb stays off or very dim
until a certain threshold, at which it abruptly gets brighter.

This is just piling on complication. If the effect you describe is
troublesome, you just add some constant current to the modulated
current.