Cheap, simple way to generate 200Hz sine wave

That would be a "phase shift oscillator" made from a single supply opamp. You can get 5% 200=10Hz accuracy using ordinary components without tuning.

On Wed, 15 Mar 2006 02:48:30 GMT in sci.electronics.design, Fred Bloggs wrote,

So how do you get it down from there to the 1Hz that he mentioned needing?

"You do know how to whistle, don't you, Steve?"

PN2222A

I cant see an analoge solution at that price, you would need precision components.

The cost of the circuit needs to be less than 50

Your cost indicates a commercial project (unless you are a 10 year old on an allowance). Yet, your question seems to indicate that you have little idea what you are doing.

Just what are you doing?

Hello,

I am glad you asked because I found this little program and it works awesome.

How about free! Use software forget about 2v to 3v.

Enjoy,

• * * Christopher

Temecula CA.USA

There's no way that you'll get a stable 200 Hz +/-1 Hz oscillator without expensive precision components - and even that will need tuning.

How about generating a 200 Hz square wave with digital components, then use a low-pass elliptic filter like the max7400 to chop off everything but the fundamental. Lot more than 50c but it's probably one of the cheaper solutions.

As others have noted, youy're unlikely to be able to get 1% stability (I assume you mean frequency stability) without an adjustable pot, and that's going to blow your budget, unless you're content with filing away at a resistor to tune it.

About the lowest-cost really stable solution I can think of:

a tiny crystal (62 cents, Digi-Key) an oscillator-divider chip (approx $1) a few resistors to do a simple D/A ( 10 cents) one transistor amplifier (12 cent transistor, two resistors)

Under $2. I don't think you can do much better than that, unless you go to high quantities and have a custom microcpu masked.

Let him go hand pick his components until he gets there.

Silly fellows. I assume by "no tuning" acannell simply means a fixed-frequency oscillator. Can a trimpot fit into his 50-cent budget? I assume he's talking Pacific-rim prices for huge mass- production quantities, so that should work. If not, then he has to go the cheapest uP route and accept its oscillator accuracy.

I thought he meant no need for adjustment.

Some things just aren't cheap and simple.

John

Thanks everyone for you responses. The project is a biofeedback device which uses low frequency tones. By no tuning I meant literally no tuning. I am assuming it will be too expensive to have some chinese slave tune a pot and watch a frequency counter. (well I guess a slave would be free, but who knows the way china is getting so capitalized) I like the digital method using a filter and a 'magic pwm sequence'. I had thought about doing this, basically a 1 bit digital audio recorder using cheap flash, with the original audio (i.e. 200hz tone) pre-encoded on a computer into a bitstream which 'matches' a given rc filter response to recreate the audio.I will take a look at lancasters work, I think that makes the most sense and would yield the most flexible design (i.e. easy to try different frequencies).

Am I wrong or could you just generate a 200hz square wave and feed it into a very steep slope low pass filter to get rid of all the harmonics? Yes, I realize generating the 200hz +/- 1 hz square wave to begin with is more than .50, but am I right about this being possible?

Is there really a need for low distorted sine wave? Filter the 200 off a divider being fed a crystal oscillator. 50 cents??

greg

Well some dividers have built in RC oscillators.

greg

It would probably be cheaper to have a Chinese line worker twiddle a pot for a few seconds than to find parts that will make an oscillator good for +- .5% out of the box.

Why does the freq. have to be so tightly controlled? If it's "only" biofeedback, how is the tone used? If it's just so the victim^H^H^H^H^H^Hpatient can hear a tone, I seriously doubt if a 190-210 Hz center freq. of the unit would make a difference, in which case any ol' sine wave oscillator can do it.

What exactly are you trying to accomplish?

Thanks, Rich

Probably not at 200 Hz.

Cheers! Rich