[En-Nut-Discussion] AD conversion resolution?

[Gerwin Voorsluijs]

Hi,

Maybe I didn't make myself clear, but I don't need to know if the ADC is 
linear or not, I want to know why I don't get certain values when I'm 
sure they have to be in there (voltage is very slowly varying!) Consider 
the following short int values that are in my data (and their binary 
counterparts): isn't it odd that there is no values in the range 
256-303? That was btw the way I noticed there was something wrong: the 
value would stay on 255 for a very long time while I was doing my 
voltage sweep.

  156 010011100
  158 010011110
  159 010011111
  176 010110000
  177 010110001
  184 010111000
  188 010111100
  192 011000000
  193 011000001
  195 011000011
  199 011000111
  206 011001110
  207 011001111
  224 011100000
  225 011100001
  227 011100011
  231 011100111
  240 011110000
  241 011110001
  248 011111000
  252 011111100
  254 011111110
  255 011111111
  304 100110000
  312 100111000
  316 100111100
  318 100111110
  319 100111111
  327 101000111
  335 101001111
  348 101011100
  352 101100000

Cheers,

Gerwin

Alexander Baranov wrote:
> Hi.
> If you want to estimate ADC linearity here is one of the ways to do it:
> Feed pure sine signal to it's input (with a half range offset), program ADC
> for measurements with constant sampling rate satisfying Nyquist  criteria
> and send the samples to PC through serial port. Let it be 1024 samples. Then
> you estimate the spectrum of obtained signal (e.g. with the help of Excell
> or MATLAB) and get  the linearity characteristics.
> Regards, Alex.
> ----- Original Message ----- 
> From: "Gerwin Voorsluijs" <g.m.voorsluijs at wanadoo.nl>
> To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
> Sent: Thursday, December 15, 2005 4:35 AM
> Subject: Re: [En-Nut-Discussion] AD conversion resolution?
> 
> 
> 
>>Hi Alexander,
>>
>>I am slowly turning a potentionmeter that is linked to an external power
>>source. To my knowledge that gives a continuously varying voltage and
>>therefore the AD readout should show the 10 bit resolution plus possibly
>>a little jitter.
>>
>>Alexander Baranov wrote:
>>
>>>Hello.
>>>Do you mean that you control the input voltage steps and they are
> 
> precisely
> 
>>>equal?
>>>
>>>----- Original Message ----- 
>>>From: "Gerwin Voorsluijs" <g.m.voorsluijs at wanadoo.nl>
>>>To: <en-nut-discussion at egnite.de>
>>>Sent: Wednesday, December 14, 2005 12:50 PM
>>>Subject: [En-Nut-Discussion] AD conversion resolution?
>>>
>>>
>>>
>>>
>>>>Dear all,
>>>>
>>>>I'm trying to use the 10bit AD conversion of the Ethernut and with some
>>>>trial and error I've managed to get some data out of it. The values I
>>>>get seem OK, but I'm a little disturbed by the fact that I don't get a
>>>>continuously climbing value out of it when I raise the voltage slowly.
>>>>For example, for the purpose I am using it (which I am sure has
>>>>continuous voltages!) I get the following set of "steps":
>>>>
>>>>156   158   159   176   177   184   188   192   193   195   199   206
>>>>207   224   225   227   231   240   241   248   252   254   255   304
>>>>312   316   318   319   327   335   348   352
>>>>
>>>>I know I am not using the full range of 0-5 V (I measured with a
>>>>"normal" voltmeter around 0.8-1.7 V so that seems OK)
>>>>
>>>>Does anyone have any idea what is going on? Lemme include the little
>>>>piece of code I used:
>>>>
>>>>#include <cfg/crt.h>    /* Floating point configuration. */
>>>>#include <string.h>
>>>>#include <stdio.h>
>>>>#include <io.h>
>>>>#include <dev/board.h>
>>>>#include <sys/timer.h>
>>>>#include <dev/adc.h>
>>>>
>>>>int main(void)
>>>>{
>>>>    u_long baud = 115200;
>>>>    FILE *uart;
>>>>
>>>>    u_char ad_chk;
>>>>    u_short adc_value;
>>>>    NutRegisterDevice(&DEV_UART, 0, 0);
>>>>    uart = fopen(DEV_UART_NAME, "r+");
>>>>    _ioctl(_fileno(uart), UART_SETSPEED, &baud);
>>>>
>>>>    ADCInit();
>>>>    ADCSetRef(AVCC);
>>>>    ADCSetMode(SINGLE_CONVERSION);
>>>>    ADCSetChannel(0);
>>>>
>>>>    for (;;)
>>>>{
>>>>ADCStartConversion();
>>>>while (ADCRead(&adc_value))
>>>>   NutThreadYield();
>>>>fprintf(uart, "%i ", (int) adc_value);
>>>>    }
>>>>}
>>>>
>>>>
>>>>_______________________________________________
>>>>En-Nut-Discussion mailing list
>>>>En-Nut-Discussion at egnite.de
>>>>http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion
>>>>
>>>>
>>>
>>>
>>>
>>>_______________________________________________
>>>En-Nut-Discussion mailing list
>>>En-Nut-Discussion at egnite.de
>>>http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion
>>>
>>>
>>
>>_______________________________________________
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>>En-Nut-Discussion at egnite.de
>>http://www.egnite.de/mailman/listinfo.cgi/en-nut-discussion
>>
>>
> 
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