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# Problem with driving circuit for 16*64 LED sign

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#### maboelectro

##### Newbie level 6
hi all

i have design 16*64 moving text led sign and i use multiplexing tequnic . the sign working good but i notice two problems .
first the brightness of the sign is low
second the brightness of columns that have few leds on is greater than columns that have mor leds on >
i know that my proplem is in driving circute but where excatly i dont know .
i use for drive 16 rows and 64 columns bc337 transistors and use cmos gates ic connected to 180 ohm resistors connected in turn to bases of that transistors .
and i use 12v/1a transformer for all and 7812/1a to drive led matrix and 7805/1a to drive control circute . notice : i use columns scan tequnic

thanks

help me

You'll need to over-drive the LEDs to about 60ma to get them bright enough.
So 60x64=3.84A you'll need to beef up your power supply and row drivers. Depending on your CMOS driver you may need to add transistors to them too.

PS put a more descriptive title on your message next time. Help me is useless.

janagyjr

### janagyjr

Points: 2
16*64 led sign

dear blueroomelectronics

first : you are absolutely right if i use row scan technique , but i use column scan technique , that means i have just one column will be active in any moment .
so if i try to over- drive all led in one column so the current will be 16*60 = 960 mA if all leds in one column were ON in same time .
but i think that my problem is in the duty cycle of column scan that equal 1/64
so even i over-drive the led to 60 mA >> the current through the led will be
60/64 = 0.937 mA .
so my analysis that if i want to get 20 mA in every led and with that duty cycle
the over-drive current will be 20*inverse duty cycle >> 20*64 = 1.280 A
what do you think ?

second : i already use transistors bc337 driven by cmos gates ICs through 180 ohm resistors .
thank you

Re: help me

hi

I think your you need to use row scan techniques, then your problem will be solved. why dont you upload your project so that you get right solution for it and it wiil be good help for others who want to make this.

regards

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