XR2206 Waveform Generator

[ssylee]

I'm not sure if anyone has built this circuit before (http://
www.nuxie1.com/guides/function-generator-2.html). The chip looks legit
and simple. I have hooked up an exact circuit with exact parts on
there. I have been able to see the square wave outputting at 0 to 12
V, and the frequency adjusts properly by adjusting R1 in the circuit
diagram. However, I have trouble obtaining the sine wave signal as
displayed on http://www.nuxie1.com/guides/function-generator-6.html
after playing around with the sine/triangular output switch and the
THD and symmetry adjustment potentiometers. I have been getting a
signal with a very small amplitude at best, with the frequencies that
are not responsive to the frequency potentiometer. I'm not sure what
went wrong there. I have hooked up everything correctly unless I have
used inappropriate types of potentiometers (those that induces noise
in the circuit?). Any comments on it would be appreciated.

 

[Nobody]

I'm not sure if anyone has built this circuit before
(http://www.nuxie1.com/guides/function-generator-2.html).
The chip looks legit
and simple. I have hooked up an exact circuit with exact parts on
there. I have been able to see the square wave outputting at 0 to 12
V, and the frequency adjusts properly by adjusting R1 in the circuit
diagram. However, I have trouble obtaining the sine wave signal as
displayed on http://www.nuxie1.com/guides/function-generator-6.html
after playing around with the sine/triangular output switch and the
THD and symmetry adjustment potentiometers. I have been getting a
signal with a very small amplitude at best, with the frequencies that
are not responsive to the frequency potentiometer. I'm not sure what
went wrong there. I have hooked up everything correctly unless I have
used inappropriate types of potentiometers (those that induces noise
in the circuit?). Any comments on it would be appreciated.

Does the triangle waveform work, or does it have the same problem as the
sine wave?

Are you aware that the amplitude for the sine/triangle waveforms is much
lower than for the square wave, and depends upon R3 (pin 3)? The datasheet
specifies the output as typically 60mV/KOhm (min:max = 40:80).

If both triangle and sine exhibit the same problems, check the circuitry
connected to pin 3. If triangle works but sine doesnt, check the switch
and resistor between pins 13 and 14.

 

[ssylee]

Does the triangle waveform work, or does it have the same problem as the
sine wave?

Are you aware that the amplitude for the sine/triangle waveforms is much
lower than for the square wave, and depends upon R3 (pin 3)? The datasheet
specifies the output as typically 60mV/KOhm (min:max = 40:80).

If both triangle and sine exhibit the same problems, check the circuitry
connected to pin 3. If triangle works but sine doesnt, check the switch
and resistor between pins 13 and 14.

Hi,

I have supplied my circuit with 22 V. It appears that I'm only getting
a triangular wave, even though I have looked at pins 13 and 14 (I
could try changing the potentiometer there). The sine/triangular wave
is about 10 V p-p with a few volts of offset from the ground. I have
been able to vary R3 to change the amplitude to have the sine/
triangular wave max out at 10V p-p. Something is not right with the
offset, although I'm not sure what I can do about it.

Cheers,

ssylee

 

[Robert Baer]

I'm not sure if anyone has built this circuit before (http://
www.nuxie1.com/guides/function-generator-2.html). The chip looks legit
and simple. I have hooked up an exact circuit with exact parts on
there. I have been able to see the square wave outputting at 0 to 12
V, and the frequency adjusts properly by adjusting R1 in the circuit
diagram. However, I have trouble obtaining the sine wave signal as
displayed on http://www.nuxie1.com/guides/function-generator-6.html
after playing around with the sine/triangular output switch and the
THD and symmetry adjustment potentiometers. I have been getting a
signal with a very small amplitude at best, with the frequencies that
are not responsive to the frequency potentiometer. I'm not sure what
went wrong there. I have hooked up everything correctly unless I have
used inappropriate types of potentiometers (those that induces noise
in the circuit?). Any comments on it would be appreciated.

For starters, there is no pot labelled THD.
Second, try no load at output (10Meg scope probe is good enough
approximation).

 

[ssylee]

For starters, there is no pot labelled THD.
Second, try no load at output (10Meg scope probe is good enough
approximation).

Hi Robert,

The THD pot I meant to point out refers to R3 on the diagram.
Secondly, I looked at the output with no load at the output, although
I don't know what's the impedance of my scope.

ssylee

 

[Nobody]

The THD pot I meant to point out refers to R3 on the diagram.

R3 controls the triangle/sine amplitude. The THD control is the one
between pins 13 and 14, labelled RA on the website (it's labelled "THD
Adjust" in the data sheet).

Essentially, a lower resistance between pins 13 and 14 rounds off the top
of the waveform. If pins 13 and 14 are open-circuit (S1 open), you get a
triangle waveform. With a low resistance (S1 closed, RA in effect), the
triangle peaks are rounded to give a sine wave (the sine wave should be
roughly half the amplitude of the triangle wave for any given value of
R3).

My first guess would be that either the IC is faulty or that closing the
switch is causing a short between pins 13 and 14, pulling the peaks down
to near zero rather than to only half the triangle amplitude.

Are you using the original schematic from page 2, or the version with
more complex THD control shown on page 4 (and used for the PCB layout)?
Have you made a PCB or is this on breadboard?

In any case, the first thing to check is whether pins 13 and 14 are being
shorted when S1 is closed.

 

[Jamie]

I'm not sure if anyone has built this circuit before (http://
www.nuxie1.com/guides/function-generator-2.html). The chip looks legit
and simple. I have hooked up an exact circuit with exact parts on
there. I have been able to see the square wave outputting at 0 to 12
V, and the frequency adjusts properly by adjusting R1 in the circuit
diagram. However, I have trouble obtaining the sine wave signal as
displayed on http://www.nuxie1.com/guides/function-generator-6.html
after playing around with the sine/triangular output switch and the
THD and symmetry adjustment potentiometers. I have been getting a
signal with a very small amplitude at best, with the frequencies that
are not responsive to the frequency potentiometer. I'm not sure what
went wrong there. I have hooked up everything correctly unless I have
used inappropriate types of potentiometers (those that induces noise
in the circuit?). Any comments on it would be appreciated.

You damaged the chip?
I looked up that chip number before. The output is suppose to
be 6V p-p, either that was a miss print or, yours having that
much output is in error!
Make sure you have a by pass cap at the Vcc and ground (common).
something like a .1 non electrolytic type.
and maybe you should try another chip.