Simple Analog -- Could Use Some Help

JonnyMac · 2020-03-23 23:51

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 · 2020-03-24 00:26

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 · 2020-03-24 00:28

Disregard please/

ozpropdev · 2020-03-24 00:36

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

JonnyMac · 2020-03-24 00:37

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

pmrobert · 2020-03-24 00:37

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 · 2020-03-24 02:31

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

Simple Analog -- Could Use Some Help

Comments