I am trying to implement pulse oximeter circuit. I am using LM358 as an amplifier. My analog circuit works well but I am giving this output to Arduino analog input- and because of the fact that Arduino could not get negative voltage as an input, I should generate positive DC offset in the analog output(or output of LM358). I give 0.1V DC input bias and 100mVpp sinusoidal signal(to simulate pulse oximeter sensor output) but the output saturates at 5V, even if the supply voltage of LM358 is 12V. Why it saturates?
And if is there any suggestion to obtain AC voltage which average voltage is not 0V, I'll be very glad. I am very confused about how can I obtain positive DC bias for my circuit output.
PS: I attached the amplifier circuit to this post.
Thanks in advance. Duygu