Variable Freq Sin Wave Generator?
Variable Freq Sin Wave Generator?
(OP)
Folks,
Sort of a newbie to this side of the forum, I lurk around the Power Eng. I'm a sys protection EE (utilities)by profession and audio/musician geek at heart. Anyhow, I'm working on an audio processing project in which I need to create a variable freq sine wave oscillator to modulate the output of an amplifier AND/OR multiple amplifiers. I'll be working in +/- 9VDC range for power supplies, so something 2 to 8 VAC range is sufficient. I'm more partial to analog devices, its been a while since the up days and frankly it turns me away. I'd like something simple to create a sinusoidal wave and to have a circuit to take that same wave and introduce 0 to 360 deg of phase shift by means of a pot resistor. Then use both of these signals to control outputs of multiple amplifiers ( something like VCA's? ) Also, I'd like to have separate controls over the frequencies of the waves and also control the speed (or time) it takes to change states. For instance... say the low freq is 20Hz, and the higher freq is 200Hz.. I'd like to have control over how it ramps up to and down between the those two. This is starting to get long.... so I'll stop now. Anyhow, looking for something minimal to create:
1. Sin/Cos wave
2. Introduce phase shift between two waves
3. Manual control over the phase shift
4. Manual/separate controls over each of those waves' freq.
5. Manual control over transistion from low to high freq & vice versa.
Thanks for any help or suggestions! I can hopefully trade out with any relaying questions you may have!
Scott
Sort of a newbie to this side of the forum, I lurk around the Power Eng. I'm a sys protection EE (utilities)by profession and audio/musician geek at heart. Anyhow, I'm working on an audio processing project in which I need to create a variable freq sine wave oscillator to modulate the output of an amplifier AND/OR multiple amplifiers. I'll be working in +/- 9VDC range for power supplies, so something 2 to 8 VAC range is sufficient. I'm more partial to analog devices, its been a while since the up days and frankly it turns me away. I'd like something simple to create a sinusoidal wave and to have a circuit to take that same wave and introduce 0 to 360 deg of phase shift by means of a pot resistor. Then use both of these signals to control outputs of multiple amplifiers ( something like VCA's? ) Also, I'd like to have separate controls over the frequencies of the waves and also control the speed (or time) it takes to change states. For instance... say the low freq is 20Hz, and the higher freq is 200Hz.. I'd like to have control over how it ramps up to and down between the those two. This is starting to get long.... so I'll stop now. Anyhow, looking for something minimal to create:
1. Sin/Cos wave
2. Introduce phase shift between two waves
3. Manual control over the phase shift
4. Manual/separate controls over each of those waves' freq.
5. Manual control over transistion from low to high freq & vice versa.
Thanks for any help or suggestions! I can hopefully trade out with any relaying questions you may have!
Scott





RE: Variable Freq Sin Wave Generator?
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Variable Freq Sin Wave Generator?
You said you are partial to AD, who makes a wide variety of DSP kits. Theri website should have plenty of information on them.
RE: Variable Freq Sin Wave Generator?
Scott
RE: Variable Freq Sin Wave Generator?
If you read the post again, his partiality was "analog devices" (lower case, as in analog components), not "Analog Devices" (capitalized, as in the chip manufacturer)
Dan - Owner

http://www.Hi-TecDesigns.com
RE: Variable Freq Sin Wave Generator?
RE: Variable Freq Sin Wave Generator?
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If we learn from our mistakes I'm getting a great education!
RE: Variable Freq Sin Wave Generator?
Various versions can output anything from microHertz to hundreds of MHz with quadrature output and 48 bit tuning control, all with quartz crystal frequency accuracy.
For a more analog approach, here's a TI app note that may help.
www.
Scroll down to the quadrature oscillator, that's the heart of what you want. National has similar app notes, this was just at the top of my Google search.
Introduce variable phase shift by summing appropriate amounts of sine, cosine, -sine and -cosine. You can also build a simple all-pass phase shifter, but then the phase shift will vary depending on the frequency.
The control for frequency is resistor and capacitor values, but with a little more digging, look up transconductance amplifiers, like the LM13700, which will allow you to vary parameters with a voltage control if you need that.
Another fun chip is the Maxim MAX083. Based on the old Intersil 8038. A wide range voltage controlled oscillator with sine, square and triangle outputs.
RE: Variable Freq Sin Wave Generator?
You might want to look at the Exar XR-2206 Monolithic Function Generator. They are a little hard to find although Jameco has them. A quick search on the internet mentions Mouser as well.
This is a tri output VCO. Sine, ramp and pulse outputs. Frequency control is via variable resistor and caps. The frequency and amplitude can be modulated.
I built a simple function generator with this chip and it has served me well. Please note that the output is high impedance and should be buffered before use.
Hope that this helps!
Cheers,
Rich S.
RE: Variable Freq Sin Wave Generator?
I am still pretty sure that a fully analogue solution which can generate a pair of sinusoids with variable phase and variable frequency will be a tricky circuit to design. In the 'old days' - when I was at college
http://www.fbk.com/test-measurement/vpg608.asp
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If we learn from our mistakes I'm getting a great education!
RE: Variable Freq Sin Wave Generator?
These typically have a VCO along with sine, triangle and square wave outputs. The duty cycle is also adjustable producing some interesting waveforms fairly simply.
www.exar.com/Files/Documents/XR2206v103.pdf
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1257
RE: Variable Freq Sin Wave Generator?
RE: Variable Freq Sin Wave Generator?
RE: Variable Freq Sin Wave Generator?
If it's sufficient to re-adjust the phase if you change the frequency, then an "all pass" filter should work. A simple circuit with an op amp, a variable resistor, two fixed resistors and a capacitor will yield up to 90 degrees pase shift. A quad op amp, ganged quad potentiometer and a handful of components will give you 360 degrees.
(Why does Eng Tips edit in a mono-spaced font and then post in a differently kerned font? This will look horrible, but if you copy the text and past it into a text document and convert it to a mono-spaced font, it should make some sense)
---+---[R]---+---[R]--+
| | |
| +--|\ |
| | >---+---
+--[pot]--+--|/
|
[C]
_|_
You might need to switch in different values of capacitor to cover the full audio range. Besides the phase being a function of frequency, it will also be rather nonlinear.
Again, using a bank of operational transconductance amplifiers instead of potentiometers may make things easier and cheaper. I haven't looked at quad pots in a while.
RE: Variable Freq Sin Wave Generator?
.-. .-.
. . .
.__. . .
*-variable phase shift
can this be done? In my mind, it seems like I need a time delayed, unlatching relay that would pass the top half of the wave, depending upon a time dial setting. Maybe the original sine wave can be a controlling parameter to allow a secondary circuit to pass the wave, based on a setting. I'm open to any possibilities to make this happen! Thanks again,
RE: Variable Freq Sin Wave Generator?
If you are using the XR2206 function generator chips suggested above, that would probably be how I would do it.
One XR2206 would be the "master" that sets the operating frequency. The other "slave" would form part of a phase locked loop.
If you compare the square wave outputs from both these chips in a phase comparator, using an XOR logic gate, and add in a dc offset (phase) adjustment, normally only 90 degrees total phase range will be possible. But if you divide both these square wave frequencies down with flip flops before doing the phase comparison, it should then be possible to get 180 or 360 degrees of total phase adjustment range.
RE: Variable Freq Sin Wave Generator?
Here's one for £75: http://www.telnet.uk.com/signal.php3
And another for about £100: ht
Unless you're building this for the fun of building it rather than building it as a necessary evil for whatever the application is (music stuff goes way over my head) the costs look fairly reasonable. Might depend where you are for shipping costs - I don't recall these as being particularly heavy, so international shipment might be an option.
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If we learn from our mistakes I'm getting a great education!