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.
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
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
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You can also use this simple 8-bit DAC with the DEMO driver that comes with the standard Daqarta for DOS download and use the built-in signal generator to 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 dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis
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