analog circuit to compute sine of voltage

[Robert]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum. However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

Thanks, Robert

 

[D from BC]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum. However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

Thanks, Robert

Isn't that a VCO?
XR2206 came to mind... Dunno if that old chip is still around.


D from BC
British Columbia
Canada.

 

[Robert]

Oh, and by the way, an input voltage range corresponding to -180
degrees to +180 degrees is sufficient.

 

[Robert]

Isn't that a VCO?
XR2206 came to mind... Dunno if that old chip is still around.

Actually, I don't want the circuit itself to be an oscillator, just
to produce the sine of a given input voltage. That is, if the input
voltage is fixed over time, then so would the output be. I imagine
analog computers must have had circuits like this in the old days...

 

[D from BC]

Oh, and by the way, an input voltage range corresponding to -180
degrees to +180 degrees is sufficient.

Oh... a phase shifter for sin.

I'm not sure but, isn't that some quirky thing of electronics where
the signal is distorted to give the appearance of a different initial
phase?

It's phasey but dunno if it's good enough...
Patent 3571732
http://www.google.com/patents?id=pNB0AAAAEBAJ&printsec=abstract&zoom=4&dq=3571732#PPA729,M1
The output is square though. Filter it for sine?
The idea here can be IC'ized if crafty at electronics

I suppose a hardcore solution would be using a DDS chip.

Beats me.. just tossing out ideas..


D from BC
British Columbia
Canada.

 

[Phil Hobbs]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum. However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

Thanks, Robert

Analog Devices used to make a dedicated chip for this, the AD639. It
worked pretty well, too. RIP.

Cheers,

Phil Hobbs

 

[D from BC]

Actually, I don't want the circuit itself to be an oscillator, just
to produce the sine of a given input voltage. That is, if the input
voltage is fixed over time, then so would the output be. I imagine
analog computers must have had circuits like this in the old days...

Oops .. ignore my 2nd post..

It's typical.. but I'll say microcontroller.
Onboard A/D converter >math (or look up table) > DAC
Often that's too heavy for most.

As for analog computing with op amps, I'm only familiar with add,
subtract, multiply and divide.

Sine series is
3 5 7
sin(x) = x - x + x + x .....
- - -
3! 5! 7!

Ugh.. I wouldn't want to do that with op amps..


D from BC
British Columbia
Canada.

 

[Robert]

Analog Devices used to make a dedicated chip for this, the AD639. It
worked pretty well, too. RIP.

I found a data sheet at http://www.analog.com/UploadedFiles/Obsolete_Data_Sheets/55889558331308887AD639.pdf
.. That's EXACTLY what I need.
Darn, it's discontinued!

 

[Frank Buss]

I found a data sheet at http://www.analog.com/UploadedFiles/Obsolete_Data_Sheets/55889558331308887AD639.pdf
. That's EXACTLY what I need.
Darn, it's discontinued!

In the datasheet there is a patent cited, where you can see the schematic:

http://tinyurl.com/2sttpm

If you want to build it for your own usage, you can use this patent without
paying for it (at least this is the regulation in Germany). But you may
need many parts.

What are your frequency, delay and precision requirements? As D from BC
suggested, with a microcontroller it would be easy.

 

[D from BC]

You still don't get it Eh? Funky Canadian, two times errors means you're a dumbfuck. An Analog!!! Got it? Not a digital. He's talking about Opamp/transistor circuit, The answer is Yes, there is a circuit that will do what he wants, it need to be implemented. Why should I tell? this isn't easy, If I am paid, yes I can do it for him.

You can filter my posts if you don't like'm..


D from BC
British Columbia
Canada.

 

[D from BC]

In the datasheet there is a patent cited, where you can see the schematic:

http://tinyurl.com/2sttpm

If you want to build it for your own usage, you can use this patent without
paying for it (at least this is the regulation in Germany). But you may
need many parts.

What are your frequency, delay and precision requirements? As D from BC
suggested, with a microcontroller it would be easy.

For sure.. I'd rather learn assembly from scratch than do trig with op
amps.
There's probably a sin math assembly routine downloadable somewhere.
If so, I'd say that's 90% of the work done.

This might be an example of how ugly it gets with
op amps:
http://www.national.com/an/AN/AN-30.pdf
Figure 4 Cube generator. 4 op amps 4 transistors.
That helps with the 1st part (X^3/3!) for the series for sin.
The other ^/! parts are needed for more accuracy.


D from BC
British Columbia
Canada.

 

[Frank Buss]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum. However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

This means the delay and frequency of the input voltage changes are low.
One idea would be to build a sine oscillator and a sample-and-hold circuit,
which samples the sine output after some time n, starting from zero
crossing from low to high, where n is proportional to the input voltage. I
don't know how to build this, but should be straight forward to design for
an analog expert, maybe with two quad op-amps.

 

[J.A. Legris]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants.  It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum.  However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

Thanks, Robert

See figure 8 on p.7:

http://my.ece.ucsb.edu/bobsclass/2C/tutorials/App notes/an-263.pdf

 

[Spehro Pefhany]

Oops .. ignore my 2nd post..

It's typical.. but I'll say microcontroller.
Onboard A/D converter >math (or look up table) > DAC
Often that's too heavy for most.

As for analog computing with op amps, I'm only familiar with add,
subtract, multiply and divide.

Sine series is
3 5 7
sin(x) = x - x + x + x .....
- - -
3! 5! 7!

Ugh.. I wouldn't want to do that with op amps..

It's possible to do a few terms of the Taylor series with multipliers
and such like, but I agree that digitally makes the most sense unless
there are some really weird constraints.

There was once a demand for that sort of thing.. hence this (obsolete)
chip from AD:

http://www.analog.com/UploadedFiles/Obsolete_Data_Sheets/55889558331308887AD639.pdf



Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

Analog Devices used to make a dedicated chip for this, the AD639. It
worked pretty well, too. RIP.

Cheers,

Phil Hobbs

I should have scrolled down first..


Best regards,
Spehro Pefhany

 

[Vladimir Vassilevsky]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

Depending on the accuracy and the stability required, you can make a
piecewise approximation of sin in the range of +/- Pi/2 using an opamp with
the diodes in the feedback path or something like that.

The more accurate solution would be the following:

1. Generate a frequency
2. Divide it by triggers to get the phases 0, 90, 180, 270.
3. Pass the phases through the VCAs controlled by the input voltage. Then
add them together. So the resultant phase would be controlled by the input.
4. Synchronously rectify to get the desired Sin(x) output.

And, of course, you can make Sin(x) by a microcontroller.

Vladimir Vassilevsky
DSP and Mixed Signal Consultant
www.abvolt.com

 

[Fred Bloggs]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage a * sin (b * v), where a
and b are constants. It doesn't matter to me what a and b are, since
I can always scale the input/output voltages appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum.
However, even a low-power circuit involving op-amps, say, would be
okay, since I could always feed the output into some large power
transistors etc.

This sounds very interesting, especially so because you exhibit the
fortitude ( or maybe the cluelessness, dunno ) to attempt a purely
analog solution. There may be some confusion on dependent system
variables here though. By driving a motor in simulation of a pendulum,
you are really talking about the angular displacement of the motor
shaft, for which measurement you have a shaft encoder, and this is the
output you want to control. The angular displacement is the double
integral of the torque which in turn is proportional to the motor
current drive. This arrangement then naturally lends itself to what is
called an implicit analog circuit representation of the second order
differential equation of angular displacement variation in time, but
there are some details to work out to simulate a lossless
self-sustaining oscillatory system, and I suspect you may be talking
about large displacements for which the equation is nonlinear.

 

[Jim Thompson]

Analog Devices used to make a dedicated chip for this, the AD639. It
worked pretty well, too. RIP.

Cheers,

Phil Hobbs

Yep. I used that part some 30 years ago to make a function generator
for GenRad's portable testers.

I still have that schematic somewhere here. If anyone wants to see
it, let me know, and I'll scan it into a PDF... it's only on paper
right now.

...Jim Thompson

 

[Fred Bloggs]

Yep. I used that part some 30 years ago to make a function generator
for GenRad's portable testers.

I still have that schematic somewhere here. If anyone wants to see
it, let me know, and I'll scan it into a PDF... it's only on paper
right now.

...Jim Thompson

Sure, I like collecting schematics of antique solid state electronics...

 

[MooseFET]

Hello -- Can anyone tell me how to make an analog circuit that takes
in a signed voltage v and produces a voltage
a * sin (b * v), where a and b are constants. It doesn't matter to me
what a and b are, since I can always scale the input/output voltages
appropriately.

The application is to drive a large D.C. motor, where the argument to
the sin function is given by a potentiometer connected to the shaft,
in such a way that the motor simulates a swinging pendulum. However,
even a low-power circuit involving op-amps, say, would be okay, since
I could always feed the output into some large power transistors etc.

If you don't mind the function having knees in it, you can do a fairly
good job with a couple of packages quad of rail to rail op-amps. Each
op-amp amplifies the input voltage with a different gain. The outputs
of the op-amps are summed together with resistors.

Near zero volts all of the op-amps are providing gain so the slope of
F(X) is large. As you move away from zero, the op-amps start hitting
the rails (each in turn) and reducing the slope of F(X). When the
lowest gain op-amp hits the rail, you are at the peak.

With two packages of quad op-amps, you can do a 16 point curve.