Greetings,

I am an amateur in this things and I am stuck with this problem:

I want to interface a signal to an ADC, but the signal is outside the limits of my ADC. So, what I am trying to do is basically, without altering the original signal to run it through a buffer (built with an op amp) and remove some of the original DC offset.

The signal has currently a base DC offset of 4.5 V and the voltage amplitude ranges from 3 - 6 V. My ADC operates between 0 - 3.3 V, so I was thinking that a new 1.7 V or 1.8 V offest would be appropriate.

I have tried to build myself some home-brew circuits starting from various schematics found on the internet, modified to suit my needs. I don't know where I am wrong - either at calculating the circuit or at the build phase - I could not obtain what I desire.

Please tell me if what I try to do is realisable and if yes please point me to a working schematic and tell me what would I need to modify or to take account of.

Also, maby this is not the only approach, so if you got other suggestions you're most welcome to tell me about it.

Last but not least maby you have knowledge of some parts that would simplify my design and eliminate build error.

Thank you very much !

Regards.

 

This sort of buffering with an op amp is standard. The web should help you find circuits that work. Also do not drive the converter outside the specs.

This might be useful:

http://www.opencircuits.com/Basic_C...uilding_Blocks#ADC_Voltage_Protection_Circuit

 

Hello and welcome.

If your 3 to 6 volt AC signal riding on 4.5VDC is fed to a voltage divider couple of resistors, you can attenuate it to the desired 3.3VAC maximum.

Applying such attenuated signal into a capacitor; and after the capacitor, a second voltage divider couple of resistors between 3.3VDC and ground, say 10KΩ each will make the attenuated 3.3VAC ride on 1.7VDC to feed the ADC converter.

Miguel