Table LED Matrix, Weeks of debugging, column problems

[mekohler]

I don't think using the ULN2004 chip would require recoding. Would the replacement of the 74LS require the coding for the PIC to be different? Should I use an inverter, and if so, can you recommend one? I have been working on this for so long I am losing my mind haha. Here is the sample code I am using

#include <pic.h>


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

int i, j, k, n, Dlay, CurLetter;

const char Letters[] = {
	
	0b0000001, // A
	0b0000001,
	0b0000001,
	0b0000001,
	0b0000001,
	
	0b0000010,
	0b0000010, // B
	0b0000010,
	0b0000010,
	0b0000010};

main()
{
	PORTA = 0;			// All Bits are Low
	PORTC = 0b000001;	// Start With Top Left
	CMCON0 = 7;			// Turn Off Comparitors
	ANSEL = 0;			// Turn Off ADC
	TRISA = 0b101000;	// RA5/RA3 Inputs
	TRISC = 0;
	
	CurLetter = 0;		// Start With "A"
	
	while (1 == 1)		// Loop Forever
	{
		for (Dlay = 0; Dlay < 25; Dlay++)
		 for (i = 0; i < 5; i++)
		 {
			 j = Letters[(CurLetter * 5) + i];
			 k = (j >> 2) & 0b010000;
			 PORTC = j & 0b111111;
			 PORTA = k + i;
			 for  (n = 0; n < 259; n++);	// 4ms Delay
		}

	CurLetter = (CurLetter +1) % 2; //Increment Letter
	}
}

If you have the time, a quick schem would be great. I am new to all of this, this is my first project. thanks!

[Ioannis]

The ULN chip is inverter! Of course you will have to change the data driven to output of PIC. Just reverse 1's and 0's.

Ioannis

[jukeman]

Does the 74LS138 and 74HC138 see data in different ways. Is it truly a drop in replacement?

[mekohler]

Before I go about trying to implement some of the suggestions, can anyone explain to me why my row's, when activated, only go to .98V? Also the ouput to my decoder from the PIC is at a constant 1.98, 1.98, .98 V (3 ouputs controlling 5 columns). Why is this so? I posted the code in a few posts back.

[jukeman]

Is there a pnp driver just the opposite of the ULN2004?

[Ioannis]

Before I go about trying to implement some of the suggestions, can anyone explain to me why my row's, when activated, only go to .98V? Also the ouput to my decoder from the PIC is at a constant 1.98, 1.98, .98 V (3 ouputs controlling 5 columns). Why is this so? I posted the code in a few posts back.

How are you measuring that voltage? By Multimeter or Oscilloscope?

Ioannis

[mekohler]

Voltmeter. I have the ground pin connected to the ground of my PSU and the + to the ouput of the respective pin on the PIC. Could it be something in the coding? I am also using the Return output of my PSU for ground.

[Ioannis]

You cannot measure the pulses with just an voltmeter. You need for sure an oscilloscope.

The measurement is an "average" of the pulses. So that value sounds OK on a voltmeter.

Ioannis