I want to make a pure AC Sinusoidal current source with variable frequency(2 Hz to 6 Hz) and variable RMS value(2 mA to 6 mA). I am using Arduino to generate sinewave and for controlling the output. I want to know that how to generate the bipolar current source using Opamps and other transistors ?
To make, DC current source I am using the circuit below.
Is there any way that the current of required amplitude and frequency can be generated using Opamps and Transistors?
Best Answer
You can make a decent sinus lookup table in software (might be what you are doing already but a bit unclear), and have the arduino step through it at varying rates to get the frequency you want. You will find even some generators for it online. A scaling factor can change the amplitude for you (but keep in mind that the harmonics and "pureness" gets worse as the amplitude is smaller). Some filtering before the constant current source will clean the edges a little bit for you as well. It wont be pure sinusoidal wave the mathematical sense, it will have harmonics, but you can get pretty close. How good it is depends on how large the table is, the number of steps.
Example generator
http://www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml
As for doing both the amplitude and frequency through pure hardware, is a bit more complex actually. And you will need two mechanisms to control this separately from the ardunio, analog or pulse train based. But both voltage-to-frequency conversion and scaling the amplitude both at the same time is not trivial in the sense it will take a bit of design effort. Maybe someone is lying on a good template for you, but this is where custom design insight might be needed.