Beginners ADC offset question

I have an application where ADC input voltage is 0-3.3 V and nature of signal is mixure of sine and cosine waves. I need signal to be present
around mid point, such as, for example, sine waves with small amplitude will have zero point at 1.65V etc. How do I do that? I need like "-1.65 + 1.65V" behaviour.
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snipped-for-privacy@hotmail.com wrote:

there is no such thing as ADC unless you are talking about Aid to Dependent Children.

please re-read your question and then restate it in such a way that we may answer it.
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Other folks do not have issue with ADC, which stays for Analog-To-Digital Converter in any book. Keep reading the forum - it will come to you.
TimPerry wrote:

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snipped-for-privacy@hotmail.com wrote:

i thought this was gonna be another thing about alternating DC.
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| snipped-for-privacy@hotmail.com wrote: |> Other folks do not have issue with ADC, which stays for |> Analog-To-Digital Converter in any book. Keep reading the forum - it |> will come to you. | | <grumble>, i'd type that as A/D converter.
I see both of these ways to refer to it about 50/50.
| i thought this was gonna be another thing about alternating DC.
DC transformers and AC batteries.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net wrote:

Ignition coils. Batteries made from unobtanium. :-)
Ed
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snipped-for-privacy@hotmail.com wrote:

Not a problem, in theory and quite possibly easy in practice. You simply need to sum your input signal with a very stable dc offset voltage before presenting it to the ADC.
This could be as simple as a potentiometer (multi-turn is possible a good idea) and capacitor. The pot goes between a stable positive supply voltage and ground and its wiper goes to both the input of the ADC and to a capacitor connected to your input signal. Adjust the wiper to give the 1.65v offset needed to bring the zero point of the input signal up to the mid-range voltage of the ADC.
Or it could be something a lot more complex - it depends on the accuracy of measurement that you need and the bandwidth and source impedance of your input signals. For example, you may need to build a quite complex, low noise, reference voltage generator plus a complex low noise analogue buffer amplifier to match the impedance of the source.
--
Sue








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If your processor has a PWM with a max output 3.3V just set the PW to 50% and feed it into the ADC through a high pass filter maybe a 300ohm Res and a .1uF Cap. The noise from the PWM will give you a small amplitude sine wave.
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