Electrical – Two multiplexed 7-segment displays flickering

7segmentdisplaymultiplexerpicproteus

I'm working on a temperature sensor.
I've got:

  • LM35 (Sensor)
  • LM741 (Op-amp to amplify LM35 Vout to 5V)
  • PIC 14F458

The temperature is shown on two 7-segment displays with only one BCD converter (4511). Therefore I multiplexed these two displays.

The problem is that my 7-segment displays are flickering a lot and I don't know why.

If you want to see the simulation on Proteus: LM35 – SSD

Here's the schematic diagram on Proteus :

schematic diagram

And here's the C code on CCS.

#include <sonde2.h>
#include <math.h>

#define CONV_CST 0.48875855327
#define TRESHOLD 25
#define TENS_DISPLAY PIN_E0
#define UNITY_DISPLAY PIN_E1
#define GREEN_LED PIN_C0
#define RED_LED PIN_C1


int simpleBCDConverter(value) {
   // Shift tens from 4 bits to the left
   // So we have ([Tens] [Unity]) XXXX XXXX
   return ((value / 10 % 10 << 4) + value % 10);
}

/**
 * Convert a number of 10 bits to its BCD equivalent
 */
void bitsToBCD(int value) {
   int tens = value / 10 % 10;
   int unity = value % 10;

   output_high(TENS_DISPLAY);
   output_d(tens);
   output_low(UNITY_DISPLAY);
   delay_ms(10);

   output_high(UNITY_DISPLAY);
   output_d(unity);
   output_low(TENS_DISPLAY);
   delay_ms(10);


}

/**
 * Check temp level, and switch on the right led
 */
void checkLed(int temp) {
   // If temps is greater than treshold
   // Blinking Red LED with 555 (astable)
   if (temp > TRESHOLD) {
      output_low(GREEN_LED);
      output_high(RED_LED);
   } else { // Otherwise, green LED
      output_high(GREEN_LED);
   }
}

void main()
{
   setup_adc_ports(AN0);
   set_adc_channel(0); // A0 connecté à l'entrée analogique
   setup_adc(ADC_CLOCK_INTERNAL);
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_1|RTCC_8_BIT); // 51,2 us overflow
   setup_timer_1(T1_INTERNAL|T1_DIV_BY_1); //13,1 ms overflow

   setup_low_volt_detect(FALSE);

   int temperature;

   while(TRUE) {
      //delay_ms(10);
      // Read the value from A/N converter (10bits [0 => 1023])
      // And convert it to a range from 0 to 100 (°C)
      // 0.48 => (5 / 1023) * 100
      temperature = read_adc() * CONV_CST;

      // Check temp level
      checkLed(temperature);

      // Convert bits to BCD
      // And show temp on 7 segment displays
      bitsToBCD(temperature);
   }

}

Thanks.

Best Answer

The problem is that my 7-segment displays are flickering a lot and I don't know why.

run the display routine in a timer isr so it is updated on an fixed interval.

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