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I'm looking after an oscillator (some circuit or component) that is able to preduce sine wave in low frequencies. I need a minimum of about 0.0002Hz which means one cycle every 30 minutes.
I would suggest a micro-controller and a digital to analogue converter, use a lookup table containing the values for a sinewave and just wrtie them out through the A2D.
How about a mechanical device?
A clock could be adapted to operate a light sensitive sensor.
It is possible to make an oscillator which will run at such very
low frequencies, but they are intrinsically inacurate, and not
easy to make. Circuits having such a low natural resonance require
very ponderous component values.
If accuracy is necessary then Nigel's suggestion of outputting the
values over a half hour period, using small increments, would be
much more practical, and also as accurate as you care to make it.
If this thing has to be made in a hurry, i would use an old clock
with the minute hand changed for a disc of card cut into a shape
with a light on one side and a sensor on the other side.
Cheap and cheerfull, and as accurate as you can trim the card.
He might mean light tubes as in skylight's. It's probably controlled by some kind of louver to control the amount of light coming in. A micro controller would work fine, most have PWM output that if properly filtered will produce an analog voltage. Since you're not changing it very fast filtering would be trivial, just a large capacitor and a small resistor.
Sorry, I meant to write light bulb. a normal one.
All I want is that its power will trun on and off gradually, slowly and infinitely.
john, I like the idea of doing it with a clock.
the only problem is that I need to be able to change the cycle's period, and Ihave no idea how to do that with a clock. any ideas?
If you apply a sine-wave of DC voltage to an incandescent light bulb then the brightness will not appear like a sine-wave. When the voltage is anywhere near being low then there will be no light, then as the voltage rises it will begin to glow with a red-orange colour, then get brighter and whiter as the voltage increases more. The opposite will happen as the voltage decreases.
You need to have a bias current flowing in it so that it isn't off for too much of the time.
I'm looking after an oscillator (some circuit or component) that is able to preduce sine wave in low frequencies. I need a minimum of about 0.0002Hz which means one cycle every 30 minutes. The two frequencies together produce beats.
Hi Chui,
it is possible oneway. you recollect the theory of beats when two sine wave frequencies F and F+(delta)F of nearly same frequency( in your cas ethe difference is .0002 cycles.) are mixed you het the sside bands like sum and difference. sum canbe filtered out and what is left is a low frequency sine wave.
we used to use this technique in telecom (FDM systems) to check the accuracy of oscillators.
i was able to get a very low beat rate of i cycle in 10.5 minutes.
It will be too boaring to watch alevel meter slowly reducing level and increasing back to same ponit after a long gap.
thus Very low frequecncies can be produced by this technic.
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