AD9833 Amplitude change

[TheDice_again]

Hello I would like to be able to change the amplitude of the AD9833 output signal. The board is controlled by an Arduino micro. I've read a lot that it shouldn't work with a normal poti? Are there still other options?

[Kleinstein]

For not too high a frequency one can still use a more normal pot with not too high a resistance (e.g. 1 K) . The problem is that parasitic capacitance will also effect the amplitude for the higher frequency part.

There are variable gain amplifier chips and programmable gain amplifiers. Some multiplying DACs can be used as variable gain attenuator for the lower frequency range.

Many other DDS chips have the option to change the DAC reference voltage for a fine adjust of the amplitude.
Coarse amplitude steps can be build with relays and CMOS switches.

[TheDice_again]

which boards are these? are they as easy to program as the AD9833?
Ijust need to change the amplitude of a 50Hz signal.

[Kleinstein]

For a lower output frequencey (e.g. up to 100 kHz) a normal potentiometers is OK and also digital potentiometers work (keep in mind the signal has to stay inside the supply range).

The variable gain amplifiers come as integrated circuits and are not common to use with hooby systems like the Arduino - so no such boards. Many of the variable gain amplifers are controlled with a votlage or current.

Variable attenuators / amplifiers for the RF range come as rather expensive modules, so not suitable here.

[MarkF]

The AD9834 DDS is an example that has an external reference voltage to control the output amplitude.  (See attached app note CD0156.)

The programming for the AD9833 and AD9834 is the same. 
I built a DDS Function Gen based on the AD9834 and used a MCP4802 to control the amplitude and DC offset. 
$Re: Looking for <$50 function generator.  The external voltage reference is 0V - 1.2V.


Edit:  I don't know if those AD9834 boards bring out the ext. ref. voltage for the user to set.

[Terry Bites]

https://www.eevblog.com/forum/projects/ceramic-potentiometer-maximum-frequency/

A pot will do unless the flatness of your response is super critical.