Simple Analog -- Could Use Some Help

JonnyMac

I have this constant:

con
'          %AAAA_BBBB_FFF_PPP_PPP_PPPPPPP_TT_MMMMM_0
  ANALOG = %0000_0000_000_100_011_0000000_00_11000_0

...and this little snippet of code using a 10K pot with between 3.3v and ground, with the wiper attached to pin 40.

  pinstart(40, ANALOG, %00_1011, 0)
  
  repeat
    waitms(100)
    level := rdpin(40)
    term.fstr1(string("POT = %d\r"), level)

It works, but instead of 0..4095 I am getting 705..3389.

JonnyMac

After seeing this in another thread:

Your measurement loop should periodically run the calibrate step on every ADC pin.

...I'm guessing this is what we need to do:

con
'           %AAAA_BBBB_FFF_PPP_PPP_PPPPPPP_TT_MMMMM_0
  AIN_GND = %0000_0000_000_100_000_0000000_00_11000_0
  AIN_VIO = %0000_0000_000_100_001_0000000_00_11000_0
  AIN_PIN = %0000_0000_000_100_011_0000000_00_11000_0


pub main() | lo, hi, level

  setup()

  pinstart(40, AIN_GND, %00_1100, 0)
  waitms(100)
  lo := rdpin(40)
 
  pinstart(40, AIN_VIO, %00_1100, 0)
  waitms(100)
  hi := rdpin(40)  
  
  pinstart(40, AIN_PIN, %00_1100, 0)
  
  repeat
    waitms(100)
    level := map(rdpin(40), lo, hi, 0, 4095)
    term.fstr1(string("POT = %d\r"), level)
    
  
pub map(value, inmin, inmax, outmin, outmax) : result

'' Maps value in range inmin..inmax to new value in range outmin..outmax

  value := (value - inmin) * (outmax - outmin) / (inmax - inmin) + outmin  
  
  return outmin #> value <# outmax

pmrobert

Disregard please/

ozpropdev

Be aware the ADC can measure below gnd and above 3V3.

JonnyMac

I think we're doing the same thing -- I'm using the RevB ES and the mode bits have changed.

pmrobert

pmrobert wrote: »

You apparently need to get the GND and VIO calibration values before scaling and calculating an accurate result. Here's some very sloppy C code that worked on 2 consecutive pins on my RevA P2-ES.

/* ADC Functions */

#define adc_read_mode 0b0000_0000_000_100011_0000000_00_01111_0
#define adc_gndcal_mode 0b0000_0000_000_100000_0000000_00_01111_0
#define adc_viocal_mode 0b0000_0000_000_100001_0000000_00_01111_0

int adcgndcal[2];
int adcviocal[2];
int adc_cycles = 600;

/* Returns voltage in microvolts from one channel */
int adc_acq(pin) {
    int val;
    int start_cnt;
    int acqdelay = adc_cycles*2;
    {
        /* Read the pin value */
        val = adc_read(pin);
        /* Return uv */
        //fds.printfss("Pin %d Val %d\n\r",pin,val);
        return(val - adcgndcal[pin]) * 3300000 / (adcviocal[pin] - adcgndcal[pin]);
    }

}

int adc_read(pin) {
    //fds.printfss("Reading Pin %d\n\r",pin);
    int val;
    int mode;
    int time;
    int acqdelay = adc_cycles*2;
    int loccycles = adc_cycles;
    adc_calibrate();
    mode = adc_read_mode;
    __asm{
        wrpin mode,pin
        wxpin loccycles,pin
        dirh pin
        getct   time
        addct1  time, acqdelay
        waitct1
        rdpin val,pin
    };
    //fds.printfss("Reading Pin %d Val %d\n\r",pin,val);
    return(val);
}

void adc_calibrate()
{
    int val;
    int mode;
    int time;
    int acqdelay = adc_cycles*2;
    int loccycles = adc_cycles;
    int pin;
    for(pin=0; pin<2; pin++)
    {
        mode = adc_gndcal_mode;
        __asm{
            wrpin mode,pin
            wxpin loccycles,pin
            dirh pin
            getct   time
            addct1  time, acqdelay
            waitct1
            rdpin val,pin
        };
        adcgndcal[pin] = val;
        mode = adc_viocal_mode;
        __asm{
            wrpin mode,pin
            wxpin loccycles,pin
            dirh pin
            getct   time
            addct1  time, acqdelay
            waitct1
            rdpin val,pin
        };
        adcviocal[pin] = val;
    }
}

Tubular

What OzPropDev said is the key, the ADC has a party trick that lets it measure beyond the rails

when we take a 16 bit ADC sample (0..65535),
"0" corresponds to around -0.7v DC
"10~12000" corresponds to 0v GND
"53~55000" corresponds to 3v3
"65535" corresponds to around 4v

You're working on 12 bits, so divide the above values by 16, gives you around 700 to 3400 that you are seeing