function generator

[soundman]

Eric,

I just Trying to say you that I Made your modification on post NO 33, but U8 and its pot (R21) just change the amplitude of the output (i.e the amplitude of the waveforms),
I tried it on Protues software and then in real by my real components, And I have to tell that U8 And R21 are in a configuration so that change the amplitude, They do not change the DC OFFSET a tall! Any solution?

 

[soundman]

I am thinking on a OP-amp In summing configuration to change the DC OFFSET, What's your idea?

 

[soundman]

Here's my configuration based upon your mode,
Please take a look at the U8 & U7 section for any misunderstanding.

 

[ericgibbs]

Eric,

I just Trying to say you that I Made your modification on post NO 33, but U8 and its pot (R21) just change the amplitude of the output (i.e the amplitude of the waveforms),
I tried it on Protues software and then in real by my real components, And I have to tell that U8 And R21 are in a configuration so that change the amplitude, They do not change the DC OFFSET a tall! Any solution?

hi,
There will be some interaction with R21 and the Gain of U8, you will need to adjust R23/24 10Kpot to compensate. I was trying to keep the component count as low as possible.
If you want a high specification Function Gen it would require a complete redesign and more high spec components.
Varying R21 should change the DC offset of the output waveform.

You do realise that as you have a single supply to the OPA's that the output waveform will always be above 0V.?

I will look at your circuit..

EDIT:
Look at these images, R21 = 5K and 40K , observe the DC shift on Vout.


EDIT2:
I see you are using a 18V supply, the original circuit from the web says 9V.??
I used 12V for my sims, I will retry at 18V

 

[ericgibbs]

hi,
You have the DC select wired incorrectly on your circuit.
Look at this edited image.

EDIT:
2nd image showing circuit error.

 

[audioguru]

The funny-looking waveform is something like a sine-wave? With about 40% distortion?
Years ago I made a function generator with an ICL8038 IC and its sine-wave also looked funny. Its distortion was audible at 1%.

 

[ericgibbs]

The funny-looking waveform is something like a sine-wave? With about 40% distortion?
Years ago I made a function generator with an ICL8038 IC and its sine-wave also looked funny. Its distortion was audible at 1%.

hi agu,
Its not my circuit.
I have advised the OP that the circuit is very limited, I would use a dedicated FG IC.
I cannot make a silk purse out of a sow's ear.

 

[audioguru]

I think the XR2206 function generator IC is the only one that is still available. I have never seen one.

 

[ericgibbs]

I think the XR2206 function generator IC is the only one that is still available. I have never seen one.

Hi agu,
Cannot vouch for the quality, but eBay offerings.

xr2206 items - Get great deals on Business, Office Industrial, Musical Instruments items on eBay UK!