I am trying to experimentally find the TF of 1st order LPF implemented with op-amp. I have wired it in breadboard. I gave a step input and recorded the response. How to get the transfer function from the recorded data? is it the right approach?
Step response gives a mixture of linear low-pass with large signal behavior, e.g. due to slew rate limitations. Nevertheless it can useful to test the circuit in time domain with signals similar to that expected in the final application.
In any case it depends on the cut-off frequency to OP speed relation if you see an ideal low-pass response or something different.