# Variable Frequency Oscillator using 555 IC

Discussion in 'General Electronics Chat' started by kino-eye, Jun 16, 2010.

1. ### kino-eye Thread Starter New Member

Jun 16, 2010
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Hello Everyone,

This is my first post on this forum and I'm hoping someone might be able to offer me some advice, or at least let me know if I'm way out to lunch here.

I'm a bit of a noob at building circuits, I took some RC circuit design courses while I was in art school, but these were VERY basic. Recently I have been building optical square wave oscillators using 555 chips wired in astable mode and using a CDS resistor in the circuit to control pitch (frequency), these circuits are connected to speakers or an amplifier and used as audio noisemakers.

What I now want to build is a circuit that is powered by 9V dc and uses one 555 IC (or several if necessary) that would have variable frequency control and output in the audio range, somewhere in the range of 20Hz to 20Khz if possible, that can output a square wave, triangle wave and something that at least approximates a sine wave (doesn't need to be perfect). I don't mind if the frequency range is determined by a capacitor value in the circuit as I can always put in a switch to jump up or down in this range.

I've seen a post on this forum that is similar to what I want, so it seems to indicate it is likely possible, but I'm not sure how to go about making a circuit like this. The post I was looking at is here:

http://forum.allaboutcircuits.com/showthread.php?t=12405

I've read threads on other forums that seem to suggest that connecting the output of a 555 to a chain of op-amp integrators or low pass filters (are these the same thing?) can achieve this result, but I don't quite understand how to do this either. I have lots of TL082 op-amps chips lying around, would it be possible to make an integrator with one of these?

Any advice will be extremely helpful, I feeling a little lost on this cause at the moment. Thanks everybody.

kinoeye

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5. ### kino-eye Thread Starter New Member

Jun 16, 2010
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Thanks for all the tips. Maybe the XR2206 is they way to go. I'm assuming for my purposes, to use as an audio output device, I'd want to configure the circuit as per figure 11 in the datasheet for the ic. Has anyone had experience using one of these as an audio output, it looks like the output impedance is higher than line level, but nowhere near a mic or guitar level. Would I need an additional am to drive a speaker with this chip? Will the output voltage be to high to connect to a mixer or loud speaker?

Would there be any possibility of building an integrator or active low-pass filter using a TL082 and chaining this to the output of a 555 in astable mode to get a suitable audio range output?

Sorry if I'm asking obvious questions, I appreciate everyone's patience.

Mar 24, 2008
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7. ### kino-eye Thread Starter New Member

Jun 16, 2010
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Hi Bill. I did have a look at the hysteretic oscillator, but from the info listed it seems that it only outputs a square wave, which I've already got. I need something that will also be able of output a triangle wave and something close to a sine wave. If I'm mising some detail in the link you posted, let me know. Thanks again.

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9. ### Craig Jackson New Member

Jun 10, 2015
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The 555 produces a square wave. However you can put the square wave through two resistor-capacitor filters to create (approximately) a sine wave. The sine wave output level will be much lower than the square wave output and it may be beneficial to amplify it. Values for R and C will have to be fiddled with, and will be ideal at only one frequency, but are still useable for a range of freq's around the ideal one.

10. ### WBahn Moderator

Mar 31, 2012
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@Craig Jackson : Note that you are replying to a question that was asked and answered over five years ago. Since your response is relevant to the question we will allow it since it is possible that someone running across the thread via a search might find it useful, but in general we discourage necroposting (responding to long dead threads) for a variety of reasons, not the least of which is that the original participants receive an e-mail notification about the revival of a thread that was put to bed years ago.

11. ### Craig Jackson New Member

Jun 10, 2015
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Thanks for allowing it...I realized when I replied to it that it was asked in 2010...but I came across it 6 years too late...maybe others will too ...thanks again!