adc problem in lpc2378

Started by jithu_ag18 January 7, 2011
hi I am currently doing my project. Iam handling the mcb2300 board.I am entirely new for the ARM.

Can any one tell me how to handle the negative voltages given to the input of the ADC.Because the ADC range which I am using is 0 to 3.3V.

Actually I want to give the sine wave as an input to the ADC and read the digital values....

Also please tell me how to see the digital values from the board.

Thanks in Advance.....

An Engineer's Guide to the LPC2100 Series

--- In l..., "jithu_ag18" wrote:
>
> hi I am currently doing my project. Iam handling the mcb2300 board.I am entirely new for the ARM.
>
> Can any one tell me how to handle the negative voltages given to the input of the ADC.Because the ADC range which I am using is 0 to 3.3V.
>
> Actually I want to give the sine wave as an input to the ADC and read the digital values....
>
> Also please tell me how to see the digital values from the board.
>
> Thanks in Advance.....
>

Use this circuit:

http://www.leonheller.com/images/Bipolar-unipolar.gif

Leon

I want to give the sine wave as an input to the ADC and read the digital values which is AC not DC.

keep smiling....
J i t h u . . .
On 07/01/2011 09:36, jithendranath swamy wrote:
> I want to give the sine wave as an input to the ADC and read the digital
> values which is AC not DC.

That little circuit converts a bipolar signal to unipolar. I thought
that was what you wanted!

You'll have to write the software yourself. You should find some
examples of how to use the ADC in the Files section.

Leon
--
Leon Heller
G1HSM
--- In l..., "jithu_ag18" wrote:
>
> hi I am currently doing my project. Iam handling the mcb2300 board.I am entirely new for the ARM.
>
> Can any one tell me how to handle the negative voltages given to the input of the ADC.Because the ADC range which I am using is 0 to 3.3V.
>
> Actually I want to give the sine wave as an input to the ADC and read the digital values....
>
> Also please tell me how to see the digital values from the board.
>
> Thanks in Advance.....
>

There is NO ADC that can measure any voltage below ground.

Please read up and any ADC let alone the ADC in the LPC2378.

After you burn out a few processors, then you will understand that you can not does that.

Google is your friend, help us help you be understanding what it is you want to do first.

good luck, you're going to need it.

Also, ask your professor.

don

--- In l..., "jithu_ag18" wrote:
>
> hi I am currently doing my project. Iam handling the mcb2300 board.I am entirely new for the ARM.
>
> Can any one tell me how to handle the negative voltages given to the input of the ADC.Because the ADC range which I am using is 0 to 3.3V.
>
> Actually I want to give the sine wave as an input to the ADC and read the digital values....
>
> Also please tell me how to see the digital values from the board.
>
> Thanks in Advance.....
>

As shown on Leon's schematic, the idea is to lift the sine wave up by 5V.

There is another way with a simple op amp. Read Chapter 4 of "Op Amps For Everyone" and calculate the 4 resistors required for the circuit.

The book is a free TI download, Google for it.

With the 4 resistors, you form a little analog calculator that solves the standard linear equation: y = mx + b. Let's say you have a 10V bipolar signal; it swings through -5..0..+5. You need to rescale that 10V swing to 3.3V so 'm' (the gain) needs to be 3.3/10 (thus a gain of 0.33). That will give you a signal that swings through -1.65V..0..+1.65V. Now all you need to do is lift the signal up by 1.65V so 'b' = 1.65.

Find the proper form in the case studies of Chapter 4 such that you can solve y = 0.33x + 1.65

The TI TLV247x op amp will work on 3.3V and gets very close to the rails for input and output. If you want to be absolutely certain that the op amp isn't saturating, change the gain such that the output voltage swings from 0.1V..3.2V. That keeps you away from the corners of the transfer function.

Richard

Actually, I had a little difficulty following the intent of the illustrated circuit ;) It wasn't immediately clear (to me) if the batteries represented the incoming signal, or were an attempt to bias the incoming signal to the correct range. Given a sine wave input, my first thought would have be to capacitively couple the incoming signal to the center of a resistor divider biased around the midpoint of the ADC's input range.