multiplexing 7 segment display

[evaradharaj]

Hi,

I am using PIC 16f877a for displaying the counter which is of 0 to 9999. I am using 4 seven segment leds.

There I am having flickering problem. I have changed the delay to many numbers in milliseconds, but I can't eliminate the flickering problem.

Here I have given the code, please correct my mistake.

I am using common cathode 7 segment led and I am giving ground to the 7 segment led by means of switching the transistor(BC548).

I am using Port C0, C1, C2, C3 pins for switching transistors and port B for displaying the digits.

[Douglas Kennedy]

Well the eye can begin to see flickering at around 1/80th of a second or about 12.5 ms. You have 4 digits each with a 5ms on time so every digit gets action every 20 ms so flickering is not unexpected. Leds switch very fast so try delay values in the high us range.

[John P]

I'm not sure that the problem is the 5msec delays, though that's an awful technique. How often is this routine executed? If there's a delay in the rest of the progam, it could cause the interval between operations of the LED digits to be long enough to be visible.

I would set up a repetitive timer interrupt to run at (let's say) 400 Hz. Then every time the interrupt executes, send out the data for one digit and increment a counter that cycles through the 4 digits. That way, you will know that each digit will be illuminated for 2.5msec, 100 times a second. You aren't wasting time with the delay routine, so your processor will have more time to do other things.

[evaradharaj]

Thanks John and Kennedy for your valuable comments. For incrementing the counter I am planning to use the timer 0 interrupt.

Please tell me, can I use the in built function delay_ms() for delay between the digits shifting and timer interrupt for incrementing the count?

Thanks and Regards,
Varadharaj E
_________________
embedding innovation in engineers