0 state not actually 0

[mungoj]

Hi,
I've created a circuit board with pic32mx250 and I'm powering the it through the programmer (pickit 3). For the test, I've included a LED on one of the digital pins. Problem is, that it won't completely "turn off" and go to 0V but it has some voltage drop if it's in 0 state, so it's shinning a little but it's ok in state 1 (it's shinning in full brightness).
Is the problem in ground connection somewhere maybe? Any ideas?

 

[esp1]

hi,
Do you have a voltmeter to check the output pin voltage levels when the pin is at +V and 0V.?

Its important that the PIC's 0V pin and the cathode of the LED are connected to the same 0V.
I assume you have a current limiting resistor in series withe the LED.?

E

 

[mungoj]

They are on the same 0V (I have a ground plane over the whole circuit). Resistor in series is 4k ohm (I didn't have any lower and use the 4k one). I think this shouldn't be a problem.

- - - Updated - - -

I can't measure it right now, cuz I'm at work. But it's not so small gap between levels. I've also saw that when it's in 1 state it's stable but when in 0, it flickers a little (at really small voltage).

 

[esp1]

I've also saw that when it's in 1 state it's stable but when in 0, it flickers a little (at really small voltage).

As you say a 4K is too high a value for a LED limiter, , usually its in the order of 220R thru 560R depending upon the LED colour.
The flickering suggests that the pin maybe not be configured correctly as an I/O pin.?

 

[KlausST]

Hi,

disable the PIC internal pullup (port setup)

also be sure that no other periferal uses this pin. (programmer, RS232, I2C....)


Klaus

 

[wp100]

Hi,

Also quiet possible that your program is in a closed loop turning the led pin on and off very quickly so giving that appearance as if its glowing slightly.

 

[mungoj]

#include <stdio.h>
#include <stdlib.h>


// PIC32MX250F128D Configuration Bit Settings

// 'C' source line config statements

//#include <xc.h>
#include <plib.h>
// DEVCFG3
// USERID = No Setting
#pragma config PMDL1WAY = OFF           // Peripheral Module Disable Configuration (Allow multiple reconfigurations)
#pragma config IOL1WAY = OFF            // Peripheral Pin Select Configuration (Allow multiple reconfigurations)
#pragma config FUSBIDIO = ON           // USB USID Selection (Controlled by Port Function)
#pragma config FVBUSONIO = ON          // USB VBUS ON Selection (Controlled by Port Function)

// DEVCFG2
#pragma config FPLLIDIV = DIV_2         // PLL Input Divider (2x Divider)
#pragma config FPLLMUL = MUL_16         // PLL Multiplier (16x Multiplier)
#pragma config UPLLIDIV = DIV_5         // USB PLL Input Divider (5x Divider)
#pragma config UPLLEN = OFF             // USB PLL Enable (Disabled and Bypassed)
#pragma config FPLLODIV = DIV_2         // System PLL Output Clock Divider (PLL Divide by 2)

// DEVCFG1
#pragma config FNOSC = PRIPLL           // Oscillator Selection Bits (Primary Osc w/PLL (XT+,HS+,EC+PLL))
#pragma config FSOSCEN = OFF            // Secondary Oscillator Enable (Disabled)
#pragma config IESO = OFF               // Internal/External Switch Over (Disabled)
#pragma config POSCMOD = HS             // Primary Oscillator Configuration (HS osc mode)
#pragma config OSCIOFNC = OFF           // CLKO Output Signal Active on the OSCO Pin (Disabled)
#pragma config FPBDIV = DIV_2           // Peripheral Clock Divisor (Pb_Clk is Sys_Clk/8)
#pragma config FCKSM = CSDCMD           // Clock Switching and Monitor Selection (Clock Switch Disable, FSCM Disabled)
#pragma config WDTPS = PS1              // Watchdog Timer Postscaler (1:1)
#pragma config WINDIS = OFF             // Watchdog Timer Window Enable (Watchdog Timer is in Non-Window Mode)
#pragma config FWDTEN = OFF             // Watchdog Timer Enable (WDT Disabled (SWDTEN Bit Controls))
#pragma config FWDTWINSZ = WISZ_25      // Watchdog Timer Window Size (Window Size is 25%)

// DEVCFG0
#pragma config JTAGEN = OFF             // JTAG Enable (JTAG Disabled)
#pragma config ICESEL = ICS_PGx1        // ICE/ICD Comm Channel Select (Communicate on PGEC4/PGED4)
#pragma config PWP = OFF                // Program Flash Write Protect (Disable)
#pragma config BWP = OFF                // Boot Flash Write Protect bit (Protection Disabled)
#pragma config CP = OFF                 // Code Protect (Protection Disabled)

#define CONFIG         (CNB_ON | CNB_IDLE_CON)
#define PINS           (CNB0_ENABLE)


int main() {
int count=0;
mPORTBDirection(0);

//mPORTBSetBits(BIT_5);
while (1)
{
mPORTBToggleBits(BIT_5);
while(count)
{
count--;
}
count=1000000;
}

return (EXIT_SUCCESS);
}

This is my code. wp100, well I don't think this is problem, cuz I tried to put pin on state 0 with a simple code and LED was also flickering. I think this should be due to the floating ground somewhere.

 

[KlausST]

Hi,

maybe a problem of schematic or a bad solder joint.


Klaus