How to generate 30Hz sine wave?

Question

I'm building a voice ring modulator. Part of it involves a 30Hz carrier sine wave to modulate the voice with. Since I'm trying to build a portable device it will be DC powered, and since a function generator is not really portable or DC powered, I don't thinks that's an option.

Crystal oscillators work at the MHz range so I'm guessing that's not the way to go either. I could play a 30Hz wave on an old mp3 player and use the audio output, but if there's another way involving analog components that'd be much better. There's no need for a lot of accuracy, just any wave from 20-40Hz will probably do, I would say it doesn't even need to be really stable either.

What approach can I take?

One thing worth adding to the question is what sort of accuracy you need, would say 5% drift be OK or are you after something more precise? — PeterJ, Aug 04 '13 at 00:28
Ignacio, thank you, but the idea of this post was that I didn't want to build a whole function generator. I just need this sine wave, i was hoping it would be easier than building the whole generator. Peter, that's a good idea, it doesn't need to be accurate at all, i'll add it to the post. — freejuices, Aug 04 '13 at 00:39
Look up Direct Digital Synthesis; you can output a low-frequency sine wave from a microcontroller more accurately than a lot of analog circuits can. — user253751, Mar 11 '21 at 16:48

score 7 · Answer 1 · answered Aug 04 '13 at 04:10

7

Your friend, the Wien-Bridge oscillator.

enter image description here

Uses just opamps and resistors/capacitors. produces very clean sine waves in the low frequency range. There are many variations, with C=C1=C2, R = R1=R2, it oscillates at \$f = \frac{1}{2\pi RC}\$. Rb is a lamp used for temperature Compensation, although there are many variations don't require it, for instance, using zener regulators like such.

enter image description here

answered Aug 04 '13 at 04:10

crasic

5,797
1
20
43

6

The lamp has nothing to do with compensating for ambient temperature. Its job is allow the circuit to have high gain initially so that oscillations can start up faster, but then to reduce the gain to unity as the amplitude increases (which heats up the filament and increases its resistance). – Kaz Aug 08 '13 at 22:51

score 2 · Accepted Answer · answered Aug 04 '13 at 01:09

2

Why not just use a 555 oscillator and an RC network to convert the square wave to a sine wave?

answered Aug 04 '13 at 01:09

Brooks

98
7

I was trying to stay away of ICs because they're pretty hard to hunt down around here but that one is really easy to get. I hadn't thought of the RC filtering though, i'm just getting started at this haha. That will probably do it, thanks! – freejuices Aug 04 '13 at 01:15
2

This may or may not work well, depending on the exact requirements. An RC filter has a very gradual slope and will not cut a lot out of the 3rd harmonic. I have no idea how this will sound with a "voice ring modulator". It might be fine, or it might be crap. But one thing is for certain: the output will only be "sine-ish". – Aug 04 '13 at 04:06

How to generate 30Hz sine wave?

2 Answers2

Linked