ESP8266 Community Forum

- Wed Jun 15, 2016 7:17 am #49208 Hi

I am putting together a project that will display some numbers on some 7 segment displays. I am trying to charlieplex the 7 segment displays as this minimises the number of shift registers required.

I have code working using a Ticker that alternates 2 of the bits on the 2nd shift register which in turn activate 2 2n7000's that grounds just 1 of the 7segment displays at once.

The problem is the leds sort of pulsate a bit. The refresh rate seems ok (50hz). I suspect the ESP8266 is doing some other work and delaying the Ticker which makes one of the segments glow slightly longer causing this pulsating.

I couldn't find any examples of anyone doing what I am doing. I have tried varying the Ticker timer down to 1000 times per second (500hz) with no improvement.

code:
I have cut this down to the bare minimum, each 7seg hard coded with a number to display for testing.

Code: Select all#include <Ticker.h>

#define CLOCK   12
#define LATCH   13
#define DATA     15

Ticker charliePlexTicker;

uint8_t segment[3];
uint8_t segmentFlag = 0;
uint8_t counter = 0;

void setup() {
  pinMode(DATA, OUTPUT);
  pinMode(CLOCK, OUTPUT); 
  pinMode(LATCH, OUTPUT);
  charliePlexTicker.attach(0.008,charliePlex);
  segment[0] = 8;
  segment[1] = 9;
}

// mapping of numbers to shift regster output
const uint8_t seg[11] = {
   0b01110111,
   0b01000001,
   0b01101110,
   0b01101011,
   0b01011001,
   0b00111011,
   0b00111111,
   0b01100001,
   0b01111111,
   0b01111011,
   0b10000000
};


void loop() {

}

void charliePlex(){
  segmentFlag ^= 1;
  if (segmentFlag) {
    shiftOutFast(0b10000000);
    shiftOutFast(seg[segment[1]]);
  } else {
    shiftOutFast(0b01000000);
    shiftOutFast(seg[segment[0]]);
  }
  latch();
}


//********************************************************************************************************

void latch() { // trigger latch
  GPIO_REG_WRITE(GPIO_OUT_W1TS_ADDRESS, 1 << LATCH);
  GPIO_REG_WRITE(GPIO_OUT_W1TC_ADDRESS, 1 << LATCH);
}

//********************************************************************************************************

// function found here http://nerdralph.blogspot.com.au/2015/04/a-4mbps-shiftout-for-esp8266arduino.html 4mbit shift out
void shiftOutFast(byte data)
{
  byte i = 8;
    do{
      GPIO_REG_WRITE(GPIO_OUT_W1TC_ADDRESS, 1 << CLOCK);
      if(data & 0x01)
        GPIO_REG_WRITE(GPIO_OUT_W1TS_ADDRESS, 1 << DATA);
      else
        GPIO_REG_WRITE(GPIO_OUT_W1TC_ADDRESS, 1 << DATA);
      GPIO_REG_WRITE(GPIO_OUT_W1TS_ADDRESS, 1 << CLOCK);
      data >>= 1;
    }while(--i);
    return;
}