Thread: some help needed for ADC programming

Hi,
I am trying to get a series of LED's to light up when a qtc pressure pill is pressed, using a 16f684. I have adapted an existing ADC program to try and do this and have managed to get the LED's to light up. The problem however lies with the fact that I can not seem to get the LED's to stay at the light level wanted (using the pressure) once the QTC has been released.

I have made 4 PWM's using for loops to set the required LED brightness for each of the ADC values.

I have a basic knowledge in C programming and have tried several different ways of trying to get the light level to stay.

What do i need to do in order to keep the light level constant (indefinitely) until the QTC registers another pressure? Do I need to make a switch case/ an interupt? As previously stated my knowledge in C is limited. Any help would be greatly appreciated. The code is below;

Code:

#include <pic.h>
#include <stdio.h>
#include <string.h>

/*  cFlash.c - Simple C Program to Flash an LED on a PIC16F684

RA4 - LED Positive Connection
RA5 - LED Negative Connection

*/

__CONFIG(INTIO & WDTDIS & PWRTEN & MCLRDIS & UNPROTECT \
  & UNPROTECT & BORDIS & IESODIS & FCMDIS);


int i, j;

//#define E RC4
//#define RS RC5
//#define QTC1 RA0					//Defines QTC1 as RA0 input
//#define QTC2 RA4					//Defines QTC2 as RA4 input
//#define QTC3 RA3					//Defines QTC3 as RA3 input


const char display_portc[]= {0b00000001, 0b00000010, 0b00000100, 0b00001000, 0b00010000, 0b00100000};

const char display_porta[]= {0b00000001, 0b00000010, 0b00000100, 0b00001000, 0b00010000, 0b00100000};

int ADCresult= 0;


void manualPWM()

{
						
					 //while (1)
					//while (ADCresult<= 60)
        			for (i = 0; i < 2; i++)  //  Simple 500ms Delay
            			for (j = 0; j < 10; j++);

       				PORTC= display_portc[0];                //  LED On

       				 for (i = 0; i < 10; i++)  //  Simple 500ms Delay
            				for (j = 0; j < 100; j++);

        			 PORTC= display_portc[1];                //  LED Off
      //GODONE = 0;

}



void manualPWM2()
{
					//	while (1)	
					  //while (ADCresult<= 120)
        			for (i = 0; i < 15; i++)  //  Simple 500ms Delay
            			for (j = 0; j < 5; j++);

       				PORTC= display_portc[0];               //  LED On

       				 for (i = 0; i < 10; i++)  //  Simple 500ms Delay
            				for (j = 0; j < 55; j++);

        			 PORTC= display_portc[1];                //  LED Off
//GODONE = 0;
}



void manualPWM3()
{
						
					//while (1)
  					 //while (ADCresult<= 180)
        			for (i = 0; i < 25; i++)  //  Simple 500ms Delay
            			for (j = 0; j < 10; j++);

       				PORTC= display_portc[0];                //  LED On

       				 for (i = 0; i < 10; i++)  //  Simple 500ms Delay
            				for (j = 0; j < 55; j++);

        			 PORTC= display_portc[1];                //  LED Off
					//GODONE = 0;
}



void manualPWM4()
{
					//	while (1)	
					   //while (ADCresult<= 240)
        			for (i = 0; i < 255; i++)  //  Simple 500ms Delay
            			for (j = 0; j < 129; j++);

       				PORTC= display_portc[0];                //  LED On

       				 for (i = 0; i < 10; i++)  //  Simple 500ms Delay
            				for (j = 0; j < 1; j++);

        			 PORTC= display_portc[1];                //  LED Off
//GODONE = 0;
       }  




main()
{
	int ADCresult= 0;
    PORTA = 1;
	PORTC = 0;
    CMCON0 = 7;                 			//  Turn off Comparators
    ANSEL = 0b00000100;       				 //Pin 11- RA2 as analogue input
	TRISA= 0b0000100;         							//PortA  input
   	TRISC = 0;                  				//PortC as output
	ADCON0= 0b00001001;  	//Result left justified format, voltage reference= VDD, 
							//AN2= analogue input, initiates ADC and waiting to start conversion.
	ADCON1= 0b00010000;   	 //  For 4 Mhz, 8Tosc= 2 uS, which > 1.6 uS, the minimum requirement








    while(1)               //  Loop Forever
   {
	GODONE = 1;                				//Start conversion.
     while (GODONE== 1);   				//Wait until conversion is done.
     ADCresult= ADRESH;    			//Transfer from ADRESH to ADCresult.  


if(ADCresult< 255) PORTA= 0; 
if(ADCresult<= 30) PORTC= display_portc[0];
        
else if(ADCresult<= 60) 
{
			manualPWM();			
					
      }

else if(ADCresult<= 120) 
{
		manualPWM2();					
					  
}

else if(ADCresult<= 180)
{
						
		manualPWM3();			
  					 
}

else if(ADCresult<= 240) 
{
		manualPWM4();					
					 
       }  
              




}  //  End cFlash
}

A big thanks to anyone that can help point me in the right direction as have been working on this for a long time without any real success.

O.lewis

How is this different from your other post. Cross posting, bumping and double-posting are all poor form. Read the forum guidelines. And have a little patience. Throwing 169 lines of messy code at us for your custom embedded setup and expecting an answer in a couple hours is a little silly. This isn't a full time job for us.

Now, on to your problem. This is all speculation since I don't have a circuit or anything to go off of, and I'm unfamiliar with QTCs. I suspect your lights are messed up because you are always reading the ADC value and updating ADCresult, even when the QTC isn't pressed. You need to figure out how your program will know the QTC is pressed or released, instead of just getting the current ADC value every time. Basically, your code needs to look something like this:

Code:

if QTC pressed
    ADCresult = get ADC value
// else it keeps the last value
set_lights(pressure)

That way, you're only updating the pressure value when the QTC is actually pressed. Once it's released, you will stop updating the pressure variable but keep running your PWM routines, thus keeping the lights at the appropriate levels.

I apologise for double posting, I hadnt realised that my other post was logged, as I couldnt find it, this shall not happen again. I do realise that you are taking time out to help without the need to and this is very much appreciated. Once again I do apologise.


For TimS.

The //500ms delay is incorrect and should not read this. These delays are to provide a dimming effect on the LED's (a manual PWM) as I could not get the real PWM to work properly.

The 4 different delay (for loop) functions allow for 4 different brightnesses with the LEDs. these are to try and accomplish 25%, 50%, 75% and 100% brightness. The brightness level is judges by the amount of pressure placed on the QTC sensor. although the problem lies with the fact that once the pressure is released, the brightness goes back to full, and will not stay at the desired level (PWM)


anduril462

The QTC is set in a potential divider, going into AN2. Would it help if I posted a circuit schematic?

I believe that you are correct in saying that the ADC is always being updated, and therefore the LED are reacting only when the QTC is pressed. as previously stated I can upload a circuit schematic if necessary.

I will try to alter the code (now tomorrow as it now late in the UK) as you have suggested to see if I can achieve the desired results, as your advice would achieve the effects that I need to achieve

Thank you so much for your help so far

O.Lewis

Go ahead and try my changes. If you still have trouble, then come back and post your schematic and modified code for us to take another look at it.

Yep! posting the schematic would be good, and why didn't the builtin PWM module work?

I believe in order to get the built in PWM to work, you need to have the 16f684.inc file. I tried this and it still didnt work. I was told by my lecturer that you can make your own PWM using for loops. This seems to be the best option at the moment in order to get a working program. Once the program has been written and is working I can then go back and alter the code to enable the on board PWM. The circuit schematic will follow shortly

Cheers,

O.Lewis

Originally Posted by O.lewis

Code:

if (QTC==1);

You certainly don't want that semicolon there. It makes that if statement do nothing whatsoever.

Code:

     GODONE = 1;                				//Start conversion.
     while (GODONE== 1);   				//Wait until conversion is done.
     ADCresult= ADRESH;    			//Transfer from ADRESH to ADCresult.

Those 3 lines are what cause the ADC to read in a value and store it in ADCresult. Assuming the QTC is considered as being pressed when QTC is equal to one (as in the above code snippet with your incorrect if statement), what I was suggesting simply to wrap the ADC reading code in a simple if block, like this:

Code:

if (QTC == 1) {  // QTC is being pressed
    // only read a value from the ADC when the QTC is being pressed
    GODONE = 1;                				//Start conversion.
    while (GODONE== 1);   				//Wait until conversion is done.
    ADCresult= ADRESH;    			//Transfer from ADRESH to ADCresult.  
}
...
// now, if the QTC wasn't pressed, ADCresult has the same value it did last time through the main while(1) loop.

Brilliant thanks for explaining that! I will give that a go on Monday as am not with my code until then. I really appreciate all the help so far. Hopefully this will enable the results that are needed.

Am I correct in saying that I need to define QTC as AN2 like

Code:

#define QTC RA2                     //defines QTC as input RA2

Regards,

O.Lewis

Originally Posted by O.lewis

Am I correct in saying that I need to define QTC as AN2 like

Code:

#define QTC RA2                     //defines QTC as input RA2

Regards,

O.Lewis

Yep! if it's wired according to the posted schematic.

Is QTC digital or Analog?

Tim S.

Originally Posted by O.lewis

itCbitC

QTC is a pressure sensor called Quantum Tunnelling composite. it acts as an electrical insulator until it is pressed which allows the flow electrons.

With regards to the code, I would like the program to register the highest ADC value when pressed, and change the light brightness to the relevant level. By this I mean, a 25% pressure will cause a 25% brightness. The problem that I am having is that the brightness then falls back to zero (as you said) and this is not wanted.

stahta01

From what I understand of QTC, it provides an analog signal when pressed.

If I understand you correctly, you're want to find the max pressure when the QTC is pressed and once it stops, you want to output the corresponding LED brightness until the QTC is pressed again?

So lets start with the find the maximum part. The general approach is:

Code:

initialize max to the smallest possible number
for each element being examined
    if the element is greater than max
        set max to the value of element

The problem with using just that code is that, if I press the QTC really hard the first time, then gently every time after that, your will never reset the max to reflect the most recent press, so it will always appear as if the QTC was pressed really hard. We need to find out when the QTC goes from unpressed to pressed, so we can reset max to the smallest value and start looking again. To do this, we need to know what state we were in last time and what state we're in now. Presumably the QTC will register 0 on your ADC if it's not pressed:

Code:

initialize prev_state to 0
infinite loop
    QTC = read ADC
    if QTC is not zero
        if prev_state is 0
            reset max to smallest number
        if QTC > max
            max = QTC
    prev_state = QTC
    display LED brightness for max