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.....

# adc problem in lpc2378

Started by ●January 7, 2011

Reply by ●January 7, 20112011-01-07

--- 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

>

> 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

Reply by ●January 7, 20112011-01-07

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 . . .

keep smiling....

J i t h u . . .

Reply by ●January 7, 20112011-01-07

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

> 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

Reply by ●January 7, 20112011-01-07

--- 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

>

> 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

Reply by ●January 7, 20112011-01-07

--- 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

>

> 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

Reply by ●January 9, 20112011-01-09

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.