ADC Problem about calibration and resoultion

[poshiun_chen]

Posted on May 31, 2007 at 05:53

ADC Problem about calibration and resoultion

[poshiun_chen]

Posted on March 20, 2007 at 07:13

Hi,

I have two problems about calibration and resolution of ADC in ST7

First, In the datasheet, ST750 has the ability of 10 bit A/D converter, do I need to initialize it or the original setup of resolution is 10 bit?

Second, I got the example from ''C:\Program Files\IAR Systems\Embedded Workbench 4.0 Evaluation\ARM\examples\ST\STR75x\STR75xStdLib\StdLib\examples\ADC\Example2''.

In the readme.txt file, it describes ''Connect a variable power supply 0-3.3V to ADC Channel3(P0.17)'' in hardware environment. In software, there is only one funtion ''ADC_StartCalibration(ADC_CalibAverage_Enable)''. But I don't know how to calibrate it in hardware and software. In some cases, (Vhigh-Vlow)/1024 is gain, but now I don't know how it works and what gain it will be in the example. When input voltages are 3.25 and 2.01, the values are 787 and 41 respectively. Should it be wrong?? What should I do in hardware and software?? Thanks for your help!!

Sincerely,

Poshiun

________________

Attachments :

Example.zip : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HtAR&d=%2Fa%2F0X0000000aJr%2FlEbCQSeDRR_ycubmNCkc3gM6k.THDcmJdlOWsFlVxNs&asPdf=false

Readme.txt : https://st--c.eu10.content.force.com/sfc/dist/version/download/?oid=00Db0000000YtG6&ids=0680X000006HtAW&d=%2Fa%2F0X0000000aJt%2FEAdAsC7u8qmWOSP.7xoracKU2bbhzg5_q45hayapgvE&asPdf=false

[kaouther]

Posted on April 03, 2007 at 15:38

Hello,

>>I have two problems about calibration and resolution of ADC in ST750.

>>First, In the datasheet, ST750 has the ability of 10 bit A/D converter, do I need to initialize it or the original setup of resolution is 10 bit?

=> There is no need of initialization or configuration to setup the 10 bit resolution.

>>In the readme.txt file, it describes ''Connect a variable power supply 0-3.3V to ADC Channel3(P0.17)'' in hardware environment. In software, there is only one function ''ADC_StartCalibration(ADC_CalibAverage_Enable)''. But I don't know how to calibrate it in hardware and software.

=> If you are using the STR750-SK board or the STR750 Evaluation board MB469, for the variable power supply 0-3.3V you, already have the potentiometer connected to to ADC Channel3 .

=> what it is needed is only the software calibration which is already implemented in the example, no need for hardware

The ADC example provides a description on how to use the ADC Ananalog watchdog low and high thresholds detection.

The ADC channel3 analog input which is guarded by the Analog watchdog0, is converted in scan.

Hope it helps you.

Regards.

[xaviooo]

Posted on May 11, 2007 at 12:55

Well, it's an old topic, but I have another question :

Is it possible to convert a 5V signal with this ADC ?

(I'm using a STR750 Eval).

(My variable power supply is 2.5V - 5V).

At the moment I get :

3V3 ---> Conversion result = 1023.

5V ---> Conversion result = 1023.

Thank you in advance :)

[kaouther]

Posted on May 31, 2007 at 05:53

Hi Xavio,

The Conversion voltage range is from VSSA_ADC to VDDA_ADC. Since you are using the STR750 eval board, the maximum conversion voltage will be 3V3. This is not advised to convert a greater value than the VDDA_ADC which is in this case 3V3 and you will get the same results as the maximum conversion volatge 3V3 as tested. It is possible to convert the 5V if the mcu power supply is 5V.