My input signal is pure square wave with 1.6v,70Hz signal connoted to 12 bit ADC of STM32F429I gives the output DFT graph but showing half of the signal frequency i.e. 35 hz . please give suggestions

[Bob S]

> please give suggestions

Without details of your code, ADC configuration, etc. all we can do is close our eyes and guess.

So my blind guess is that your ADC is sampling at twice the rate your DFT is expecting. Look at your raw ADC data and see if the number of samples per period is what you expect.