I'm building a circuit that will generate various wave forms. The output from the circuit is fed to a summing amplified where positive or negative dc offset is being added. This signal should be attenuated or amplified according to what's written in code (this means no pots.). The control elements I currently have are the MCU with a few free GPIOs and a free channel on a bi-polar 14bit DAC. The solution should take in account the fact this design should be of high quality, so I am not sure using an LED+LDR combo or something like that is really an option as the control should be tight and repeatable.
Controlling an Op-amp gain using an MCU && || DAC
dacgainmicrocontrolleroperational-amplifier
Related Solutions
Simple use case: you want an output higher than the internal VREF (2.048V) but don't want to add to your parts count with an external reference.
The less obvious case is what the datasheet calls "multiplier mode". In this case you keep the digital signal fixed and feed an analogue signal into VREF. That gives you a programmable gain amplifier, and the 2*VREF mode lets you have a gain between 0 and 2. That could be useful for analogue control loops or sensor biasing.
An op-amp is not required. Given the minimal requirements given, a voltage divider will do. Gain = 0.5.
simulate this circuit – Schematic created using CircuitLab
If you need to buffer the output, you can just place a unity gain op-amp at the output of the voltage divider.
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Best Answer
You can certainly use a digital pot. You might also try a variable gain amplifier -- or maybe a switched capacitor circuit controlling a resistance value in a feedback path to change the gain by changing the switched cap clock frequency.