| Author |
Beginners ADC offset question
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| alexz4junk@hotmail.com 2006-10-20, 3:25 am |
| 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.
| |
| TimPerry 2006-10-20, 3:25 am |
| alexz4junk@hotmail.com wrote:
> I have an application where ADC input voltage is 0-3.3 V and nature of
> signal is mixure of sine and cosine waves.
there is no such thing as ADC unless you are talking about Aid to Dependent
Children.
> 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" behavior.
please re-read your question and then restate it in such a way that we may
answer it.
| |
| Palindr☻me 2006-10-20, 9:25 am |
| alexz4junk@hotmail.com wrote:
> 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.
>
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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| Mark Siegel 2006-10-20, 9:25 am |
|
<alexz4junk@hotmail.com> wrote in message
news:1161314976.212871.216220@f16g2000cwb.googlegroups.com...
>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.
>
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.
| |
| alexz4junk@hotmail.com 2006-10-20, 9:25 pm |
| 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:
> alexz4junk@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.
| |
| TimPerry 2006-10-21, 3:25 am |
| alexz4junk@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 thought this was gonna be another thing about alternating DC.
| |
| phil-news-nospam@ipal.net 2006-10-21, 9:25 pm |
| On Sat, 21 Oct 2006 01:45:14 -0400 TimPerry <timperry@noaspamadelphia.net> wrote:
| alexz4junk@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 |
| first name lower case at ipal.net / spamtrap-2006-10-21-2011@ipal.net |
|------------------------------------/-------------------------------------|
| |
|
| phil-news-nospam@ipal.net wrote:
>
>
> | i thought this was gonna be another thing about alternating DC.
>
> DC transformers and AC batteries.
>
Ignition coils. Batteries made from unobtanium. :-)
Ed
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