[General] LED Matrix display flickering

[archusvijay1]

HI,
I want to build an 64X8 led matrix display. for making that i want to first build the 8x8 matrix display using two 74595 (one for row and other for column) and 74hc595 and cd4017. if i use two 595 flickering occurs but cd 4017 has no problem

how ca i reduce this flickering effect?
if i make cd4017 based display what is the maximum size of the dot matrix display? (number of column) If any standard calculation is available for this?

 

[udayan92]

Can you give some information on how have you connected the LED matrix between the 74HC595 ICs, with a circuit diagram if you have one ?

 

[Easyrider83]

Better use MAX7219
**broken link removed**

 

[archusvijay1]

Can you give some information on how have you connected the LED matrix between the 74HC595 ICs, with a circuit diagram if you have one ?

i am not drawn the ckt diagram, its a basic diagram which one 595 connected in row and other is connected in column, data are send through the column 595,row produce the shifting operation only

Better use MAX7219
**broken link removed**

max7219 is a good option. my intention is to make a large scrolling display 16x 96, if i try to implement it using 7219 large number of 7219 is required,and the production cost is also large

 

[KlausST]

Hi,

To get a non flickering display i recommend to use a fixed timing. The wole display should be interrupt drven.

To be non flickering you need about 50 complete display updates per second.
(If this needs too much processing power look for "interlacing")
With 8 rows you need 50Hz x 8 = 400Hz interrupt.

Mind that the LEDs are driven with 1/8 duty cycle. To get more brightness you may overdrive the LED current. ( specified max DC led current)
If you see artefacts (from the previous driven row) then you may switch off all columns, then update row, then enable new column.

To calculate the max Leds per row:
The column driver must be able to supply (Led_current x Leds_per_row) worst case for the given duty cycle.

Klaus.

 

[archusvijay1]

With 8 rows you need 50Hz x 8 = 400Hz interrupt

i am run the clock speed of 4Mhz and updates is very higher than 50Hz

Mind that the LEDs are driven with 1/8 duty cycle. To get more brightness you may overdrive the LED current.

i am using 5V dc. for over driving of led is to change the voltage to 6V

The column driver must be able to supply (Led_current x Leds_per_row) worst case for the given duty cycle.

i am using ULN2804 for current sinking for each 595 maximum 8x8 (64)led is loaded.so if i use more power rated current sink ic maximum of how much 595 can be connected in column.

 

[Easyrider83]

Each 595 can provide 20mA per pin.

 

[KlausST]

Hi,

i am run the clock speed of 4Mhz and updates is very higher than 50Hz

This is exactely what i NOT recommend.

i am using 5V dc. for over driving of led is to change the voltage to 6V

Usually the current is set up with current limiting resistors.



Klaus