Tiva Launchpad ADC reading incorrect

I do not see reference settings.

Please refer to http://www.ti.com/lit/ds/symlink/tm4c123gh6pm.pdf 13.3.4.1 Voltage Reference

Regards,
Maciej 

Thanks Maciej for pointer.

I have added ADCReferenceSet(ADC0_BASE,ADC_REF_INT);

But still the value is in-between 0x140 to 0x170, no matter what is i/p voltage (0 to 3.3 volts) always getting reading in this rang. Even when I kept the pin floating still read value is in given range. 

Seems ADC reading noise or not activated correctly. ( input voltage is correctly applied externally, I have verified the voltage level on Pin).

Any suggestions??

Hi,

I think you did not configured the ADC input pin as  analog pin-try read the data sheet and/or read also the driver lib function GPIOPinTypeADC(). 

Petrei

Yes Petrei, I did it.

Forgot to mentioned in code snippet.

Void EK_TM4C123GXL_ADC(Void)
{

/* ADC0 */
SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

/* enable pin for analog input */
GPIOPinTypeADC(GPIO_PORTD_BASE, GPIO_PIN_2 ); //Fix Me


}

Ok, you haven't posted complete code therefore it is hard to tell what is missing.

To use ADC you need to:

1. Initialize clocks
2. Initialize GPIO ( I do not see GPIOPinTypeADC)
3. Initialize ADC

I apologies for not posting complete code. here is the complete code and I am having problem using this code.

#define  ADC0_SEQUENCER3   3

Void EK_TM4C123GXL_initGeneral(Void)
{
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOC);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
}

/*
 *  ======== EK_TM4C123GXL_initCOMP ========
 */

Void EK_TM4C123GXL_ADC(Void)
{

    /* ADC0 */
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);

    /* enable pin for analog input */
    GPIOPinTypeADC(GPIO_PORTD_BASE, GPIO_PIN_2 ); //Fix Me


}

Int main(Void)
{
	int i;
	FPMsgObj *msg;
	Error_Block eb;

    SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                       SYSCTL_XTAL_16MHZ);

    /* Call board init functions */
    EK_TM4C123GXL_initGeneral();
    EK_TM4C123GXL_ADC();
    ... // other init for UART, COMP1 and GPIO

ComparatorConfigure(COMP_BASE, 1, (COMP_TRIG_FALL | COMP_ASRCP_PIN | COMP_OUTPUT_NORMAL ));
ADCSequenceDisable(ADC0_BASE, ADC0_SEQUENCER3);
ADCReferenceSet(ADC0_BASE,ADC_REF_INT);
ADCSequenceConfigure(ADC0_BASE, ADC0_SEQUENCER3, ADC_TRIGGER_COMP1, 0 );
ADCSequenceStepConfigure(ADC0_BASE, ADC0_SEQUENCER3, 0, ADC_CTL_CH0 | ADC_CTL_IE | ADC_CTL_END );
ADCSequenceEnable(ADC0_BASE, ADC0_SEQUENCER3);
ADCIntClear(ADC0_BASE, ADC0_SEQUENCER3);
ADCIntEnable(ADC0_BASE, ADC0_SEQUENCER3);
Hwi_enableInterrupt(33);
BIOS_start();

return (0);
}

isr()
{
unsigned int adcValue[1];
ADCIntClear(ADC0_BASE, ADC0_SEQUENCER3);
ADCSequenceDataGet(ADC0_BASE, ADC0_SEQUENCER3, adcValue);
 
}

Thanks Kel,

It's working, able to read proper ADC values.

I didn't know that the Channel ADC_CTL_CHX must be the same corresponding AINX input we select.

Markel Robregado,
can you help me in the similar problem , i am working on the project "Acoustic Source Localisation" ,In that project I am using Two mics (MAX9812) for estimate the Direction of arrival of sound
So for I am using Adc0 sequencer 3 , and i am required to take signal from two channels (for two mics)
I have initialised as given below
void ADC0_Init(void){ volatile unsigned long delay;
SYSCTL_RCGC2_R |= 0x00000010; // 1) activate clock for Port E
delay = SYSCTL_RCGC2_R; // allow time for clock to stabilize
GPIO_PORTE_DIR_R &= ~0x05; // 2) make PE2 pe0 input
GPIO_PORTE_AFSEL_R |= 0x05; // 3) enable alternate function on PE2 PE0
GPIO_PORTE_DEN_R &= ~0x05; // 4) disable digital I/O on PE2 PE0
GPIO_PORTE_AMSEL_R |= 0x05; // 5) enable analog function on PE2 PE0
SYSCTL_RCGC0_R |= 0x00010000; // 6) activate ADC0
delay = SYSCTL_RCGC0_R;
SYSCTL_RCGC0_R |=0x00000300; // 7) configure for 1M Samplespersec
ADC0_SSPRI_R = 0x0123; // 8) Sequencer 3 is highest priority
ADC0_ACTSS_R &= ~0x0008; // 9) disable sample sequencer 3
ADC0_EMUX_R &= ~0xF000; // 10) seq3 is software trigger
ADC0_SSMUX3_R &= ~0x000F; // 11) clear SS3 field
ADC0_SSMUX3_R += 3; // set channel Ain3 (PE0)
ADC0_SSCTL3_R = 0x0006; // 12) no TS0 D0, yes IE0 END0
ADC0_ACTSS_R |= 0x0008; // 13) enable sample sequencer 3
}
I multiplex both mic signal by changing
ADC0_SSMUX3_R &= ~0x000F; // 11) clear SS3 field
ADC0_SSMUX3_R += 3; // set channel Ain3(PE0)
and
ADC0_SSMUX3_R &= ~0x000F; // 11) clear SS3 field
ADC0_SSMUX3_R += 1; // set channel Ain1 (PE2)
In the course "Embedded system "PE2 was used as channel
Now in my project adc conversion from PE2 is working properly but from PE0 even if there is no sound its adc converted data in varying unexpectedly while from that of PE2 remains quite constant when sound is applied(Pe2 is working properly)

So please tell what I am doing Wrong in this project

Hi mohd irfan,

I am not available to help at the moment, so wait for other forum members to help you.

I suggest you use Tivaware C API's. Also provide more information about your hardware set-up, like what Tiva board are you using?

- kel