ADC multiple Channel Sampling - Erroneous readings

Hi Joshua,

First, did you know you can use ADC0_BASE instead of writing the base address number? Also for the GPIO you can use GPIO_PORTF_BASE.

The ADCSequenceDataGet() takes care of loading into the array all the programmed samples. In your case is 4 samples so in resultBuffer[0] holds the first value, resultBuffer[1] the second, and so on.
So when you are doing resultBuffer[2] you are indeed just checking the 3rd sample.

Also, you are missing the config for the ADC pins. I don't quite know how to explain the behavior you are experiencing but you have to configure the GPIO as ADC inputs.

Second, why are you using direct register access to control the LEDs? The GPIO data is not that straight forward and I don't know if the the macro GPIO_PORTF_DATA_R is using the correct address to control all at the same time or the base address for controlling them (it's different).

Edit:

How far apart are the sensors? You never know exactly the value they have!
I advise you to try to monitor the value with the Code Composer Tools. Really handy! A need to learn early.
I don't quite know if it's the best document to read up that.

But try this.
Debug
Don't start the code
Set a breakpoint after ADCSequenceDataGet();
Go to "View"->"Expressions". It should open a window.
There add "resultBuffer".
Now it should be possible to see the values of resultBuffer when the breakpoint is reached. Just start the code now.

Try this to see what is your problem 

It's usually faster, easier and more productive to employ a simple voltage divider - and feed that voltage into your ADC. (Your sensor will likely exhibit wide variations due to ambient, temperature & supply voltage - that's non-ideal for ADC checkout)

A series connection of the same resistor value yields nice, predictable, equally stepped signal levels - which speed & ease your ADC analysis.

KISS - most always - proves fastest - easiest - simply best...

Thank you for your reply Luis. I really appreciate the time you are taking to help me out.

I was aware of using the base defines but I don't know which file they are stored in, so i haven't yet used them.

I added in the config function and I now use the TivaWare API to control the LEDs. I prefer to use direct register access because that is how I was first introduced to the Tiva board and I find it easier to simply write "GPIO_PORTF_DATA_R=0x04;" rather than fill in all the arguments for the GPIOPinWrite function. Nevertheless, I removed this element in order to eliminate it as a possible cause for this weird behaviour.

Here is my new source code:

uint32_t resultBuffer[4] = {0};
uint32_t *resultBufferAdd;


int main(void)
{

		//assign pointer used by ADCSequenceDataGet function to resultBuffer array
	
		resultBufferAdd = &resultBuffer[0];
		
		//ENABLE GPIO AND ADC PERIPHERALS
		
		SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
	 	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
		SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
	
		//Configure port F as output for use of multicolour LED on Tiva Board
	
		GPIOPinTypeGPIOOutput(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);

		//Configure PE1-3 as ADC inputs
	
		GPIOPinTypeADC(0x40024000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);
	
		//Configure ADC0 Sampling Sequencer 1 for 4 samples with channel Ain3 being the final channel to sample in the sequence
	
		ADCSequenceConfigure(0x40038000, 1, ADC_TRIGGER_PROCESSOR, 0);
		ADCSequenceStepConfigure(0x40038000, 1, 0, ADC_CTL_CH0);
		ADCSequenceStepConfigure(0x40038000, 1, 1, ADC_CTL_CH1);
		ADCSequenceStepConfigure(0x40038000, 1, 2, ADC_CTL_CH2);
		ADCSequenceStepConfigure(0x40038000, 1, 3, ADC_CTL_IE | ADC_CTL_END | ADC_CTL_CH3);
		ADCSequenceEnable(0x40038000, 1);
	
		while(1)
		{
				ADCProcessorTrigger(0x40038000, 1); //Begin sampling
				while(!ADCIntStatus(0x40038000, 1, false)){} //wait for sample sequence to finish
				ADCSequenceDataGet(0x40038000, 1, resultBufferAdd); //Get samples and place in resultBuffer array
				if(resultBuffer[2]>1000){GPIOPinWrite(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3, 0x4);} //if the 3rd element is over 1000, turn LED on
				else{GPIOPinWrite(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3, 0x0);}//if the third element is not over 1000, turn LED off
		}


}

When I used your method of monitoring the sample values while stepping through the program, it actually worked as expected. When I put my finger in front of an individual sensor, its corresponding sample would go up, while the adjacent sensor outputs would also increase slightly, as expected as they are very close together. However, when I just run the code and watch the samples, they are all over the place, no matter where I put my hand, they all fluctuate wildly. 

I did actually originally try to do it all using just direct register access, so I am quite well acquainted with this part of the datasheet. I also found a mistake in my code, where I did not initialise the pin corresponding to channel 0 with the  GPIOPinTypeADC function. I also thought I should specifcally make it an input using the GPIOPinTypeInput function. The new source code now has this corrected, but the same problem still remains.

uint32_t resultBuffer[4] = {0};
uint32_t *resultBufferAdd;


int main(void)
{

		//assign pointer used by ADCSequenceDataGet function to resultBuffer array
	
		resultBufferAdd = &resultBuffer[0];
		
		//ENABLE GPIO AND ADC PERIPHERALS
		
		SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
	 	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
		SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
	
		//Configure port F as output for use of multicolour LED on Tiva Board
		
		GPIOPinTypeGPIOOutput(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);
		GPIOPinTypeGPIOInput(0x40024000, GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);
		//Configure PE1-3 as ADC inputs
	
		GPIOPinTypeADC(0x40024000, GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3);
	
		//Configure ADC0 Sampling Sequencer 1 for 4 samples with channel Ain3 being the final channel to sample in the sequence
	
		ADCSequenceConfigure(0x40038000, 1, ADC_TRIGGER_PROCESSOR, 0);
		ADCSequenceStepConfigure(0x40038000, 1, 0, ADC_CTL_CH0);
		ADCSequenceStepConfigure(0x40038000, 1, 1, ADC_CTL_CH1);
		ADCSequenceStepConfigure(0x40038000, 1, 2, ADC_CTL_CH2);
		ADCSequenceStepConfigure(0x40038000, 1, 3, ADC_CTL_IE | ADC_CTL_END | ADC_CTL_CH3);
		ADCSequenceEnable(0x40038000, 1);
	
		while(1)
		{
				ADCProcessorTrigger(0x40038000, 1); //Begin sampling
				while(!ADCIntStatus(0x40038000, 1, false)){} //wait for sample sequence to finish
				ADCSequenceDataGet(0x40038000, 1, resultBufferAdd); //Get samples and place in resultBuffer array
				if(resultBuffer[0]>1000){GPIOPinWrite(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3, 0x4);} //if the 3rd element is over 1000, turn LED on
				else{GPIOPinWrite(0x40025000, GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3, 0x0);}//if the third element is not over 1000, turn LED off
		}


}