hye, i have an -/+2V ac input signal,with very low frequency range(0.1-45Hz).. Now i want to send the signal to an adc,witch only accept voltage range from 0-5V..I planned to shift the voltage(add dc offset) so that the input signal becomes 0 to +4V..is it possible if i use summing amplifier configuration(one opamp and 3 resistor) for this task? or do i need to use another circuit if the input's freqs is too low? thanks..

 

What are you interested in doing - recording the waveform, tracking the magnitude of the voltage, or tracking the frequency?

In all of the above cases, an op amp full wave rectifier can output the peaks as uniformly positive. You can also add some gain to make the voltage go 0 - 5 volts. Here is a link - http://en.wikipedia.org/wiki/Precision_rectifier

 

If you want to convert 4Vp-p AC (2V AC) to a DC signal, you can use a potential divider. Tie a 1k resistor to 5V and a 1k resistor from the other end of the first 1k to your signal - this will give you a 1V signal superimposed on 2.5V, so from 1.5V to 3.5V. If you want it to span the full range, you'll need to amplify it using an op-amp as beenthere suggests.

 

i want to record the waveform, but i need to shift the voltage level first.which means if input is -2v, output becomes 0v ; input 0v, output +2v ; input +2v,output +4v.. i want to shift the signal so that it varies from 0 to +4v ranges..

 

Try this...

Daniel.