# Generate low frequency sine wave

Discussion in 'Electronic Basics' started by [email protected], Jul 12, 2006.

1. ### Guest

Hi,

For a project, I would like to be able to generate very low frequency
sine waves, between about 0.5 to 1.0Hz in frequency. I am a beginner at
electronics.

This circuit would be useful to test a data acquisition program I am
working on, which acquires an analog signal at 10Hz. A slowly varying
sine wave would be a good test input. I would like to stay away from
square waves, because I also want to be able to check the smoothness of
the acquired signal.

Are there any simple circuit designs that could accomplish this? Any
references to further reading or links to schematic diagrams on the web
would be appreciated.

Thanks very much,
Markus.

2. ### Rich GriseGuest

There are hundreds of them. Try going to the other side of google, and
search for "oscillator circuits".

Good Luck!
Rich

3. ### jasenGuest

hook an R-2R DAC to your printer port and synthesise a sine wave.

or a microcontroller doins a PWM version of a sine wave followed by a good
low-pass filter.

or if you're feeling adventurous the PC's timer chip (drives the internal
loudspeaker) can do PWM too I think. but getting at that feature could be hard
if ypu're using a modern operating system.

getting sines that low using analogue circuitry will be real hard

Bye.
Jasen

4. ### Bob MastaGuest

I know this isn't what you asked for, but I suggest that you use a
triangle wave instead of a sine wave. It is much easier to generate
a near-perfect triangle wave than a sine wave. Plus, the accuracy
of your system is much easier to verify by eye with a triangle.
You can easily tell if a triangle is warped or compressed because
the lines are no longer straight, but it takes a huge amount of
sine wave distortion to be detectable this way.

In fact, you probably only need a sawtooth ramp wave. The
easiest way to create one is to make a simple constant
current source and use it to charge a capacitor. An op-amp
buffers the capacitor voltage to the output, and also to
a comparator. When the voltage goes over some threshold
voltage, the comparator turns on a transistor that shorts
out the capacitor, and the cycle repeats. I don't have a
circuit handy in digital format, but I'll bet you can find one
by Googling for "ramp generator circuit" or "sawtooth generator
circuit". If that doesn't work out, post back and I'll try
my hand as ASCII art.

Another option, if you have an old DOS computer handy
(Win9x or earlier) is to make a simple R-2R ladder D/A that
plugs into your printer port. You can then get 256 different
levels to test your A/D, at any rate you want including DC.
You can use the examples in the LPTX driver Help section
of my Daqarta for DOS, at
www.daqarta.com/lptx.htm
You can also use this simple 8-bit DAC with the DEMO
driver that comes with the standard Daqarta for DOS
creae all sorts of fancy waveforms, including sines and
triangles. There is no time limit on using Daqarta for
DOS with the DEMO driver, so if this meets your needs
you are welcome to use it forever. Let me know if this
is what you want to do, and I'll give some pointers.

Best regards,

Bob Masta

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator

5. ### Guest

Look up phase shift oscillators