Precision low frequency generation

( taking a computer generated stereo sinewave output with (say) one

a low

will work,

Sample & Hold one signal as triggered by the other. The trigger signal will probably need to be converted to a pulsetrain to operate the S/H - zero crossing followed by monostable perhaps?

To get the sum, difference as well as the original frequencies, you need a *nonlinear* device. Next, use a filter to remove the original frequencies and the sum frequency.

Why, pray tell, use a thousand dollar power sucking hog to do this? There are plenty of simple, small, low power discreet circuite as aell as ICs that can be used for this project.

I repeat, *WHY* waste 100 watts to generate something that can be generated using MILLIwatts and a small battery?

Dirk Bruere at NeoPax wrote in news: snipped-for-privacy@l1g2000hsa.googlegroups.com:

Excellent!

--Damon

Too bad that Dirk chooses to act like a Slowman clone.

...Jim Thompson

-- | 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 | |

What are you, siding with the Klingons?

John

I suspect that is none of our business.

Why do you believe you need to know that to reply to a simple question?

Gee, look back; i did give an answer..... Oh, what about cutting back on heat pollution (as well as other polution) by using low power devices when possible??????

You need to define precision.

How about this. You can make a simple sine wave generator feeding a square wave to a switched capacitor filter. Now if the clock for the switched capacitor filter was the output of the sound card, you would get a much lower frequency sine wave than the clock. The square wave generator is made by dividing down the switched capacitor filter clock.

Let's do a simple example. The sound card is putting out 100Hz. Let the clock to corner of the filter be 100. Now you have a filter at

The frequency of the sine wave will be very precise. Fidelity is another story. You would be doing well to get about 70db down.

There are trick you can do to reduce the harmonics fed to the switched capacitor filter. One simple trick is to feed a signal that is 1 1 1

If you have a bigger budget, use a digital sine wave generator scheme (dac and rom), where again the clock is from the sound card.

I saw a DAC on the parallel port mentioned. This doesn't work well unless you use DOS. The port control timing is not very good in modern operating systems.

Late at night, by candle light, Dirk Bruere at NeoPax penned this immortal opus:

Generate a PWM square wave at a couple 100 Hz. Then all you'll need is a LPF and whatever gain and DC block/restore required. Might try FM too.

- YD.

Because ultimately I also need the output to follow complex time dependent frequency patterns eg 6Hz to 2.5Hz over a ten minute period, followed by 2.5 to 8 over three minutes, followed by... etc

Dirk

So what would I get from linearly adding two different frequency sine waves? When I do it in Audacity (s/w) I get a signal modulated at the difference frequency.

Dirk

"Dirk Bruere at NeoPax"

This vile psychopathic pile of **S*IT** must be exterminated from the face of the earth.

It may take any number of wooden stakes, driven through this vile zombie's heart.

Show no mercy - it ain't human.

...... Phil

The mathematical identity :

sin(A) + sin(B) = 2 sin((A+B)/2)cos((A-B)/2)

Comes in useful for working this out. Substitute A = wt, B=ut to see how the frequencies produced by linear mixing are related.

w, u added together in equal amounts makes a (w+u)/2 carrier amplitude modulated (multiplied) by (w-u)/2.

If you wanted to generate a pure sine wave at a low frequency you multiply two similar frequency sine waves together. However, I reckon a sample and hold would be neater and easier.

Regards, Martin Brown

"Martin Brown"

The identity quoted above does NOT describe amplitude modulation.

It describes a quite different phenomenon called "beats."

Look it up.

You bloody need to.

...... Phil

Here's one of me and Fiona

Dirk