Hello guys this is my first post here, since long time i have seen many problems answered on this forum so here i am unable to solve a little problem for my led matrix display, please help if you can
I am using 8052 for displaying a string of letters on an led matrix that i made on dotted pcb(27 columns), i have checked each column individually by flashing all rows on each using 1k current limiting resistors, now in my design i use uln2803 for driving rows and then cd4514 for selecting columns, i have simulated the circuit using dot matrix available in proteus and it worked fine, but now when i am doing it on hardware the text is scrolling the way it is supposed to but only problem is that it is too much dim(like need to concentrate on display to see the letters moving), and after that i tried connecting without using uln2803 and the output comes same, i thought might be some problem in ic so i tried 2 other uln2803 but with same output. Can i please get any help about this?(i have tried using 500ohm as current limiting resistor after uln2803, then tried using 1k pull up resistor after uln2803 which didnt do anything either, the output comes same dimmed but it scrolls and displays what it is supposed to display)
thanks for any help you can give
8052 has internal pull up resistors on p1 p2 and p3 and i am using only p1, p2
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this is the relevant part of the circuit if u need(instead of the 74573 i am using uln2803, it was used only for simulation since proteus doesnt do uln2803 properly)
You can't use 2803 to drive both rows and columns. 2803 can only drive LED cathodes, anode side needs a PNP driver. SO i I presume your LED matrix has anodes connect to CD4514.
The other problem is that the output current of CMOS ICs is very low, probably not suffcient for reasonable LED matrix intensity, but you should see something at least.
yea man i am thinking that might be the problem, i didnt have the parts today so i am waiting to do remaining tomorrow by using 2x74154 then to 4xuln2003 and then to led matrix with common cathode columns and the common anode rows going to udn2981 then to the port of controller....just last two questions, is this configuration i wrote correct?(since using npn driver for coulmns and pnp driver for anode rows), and if it is then do i need to use 2981 on the rows or will a pull up will be alright there?
(btw thanks for helping me so far )
edit: i wrote reverse it should be 4xudn2981 and uln2003 for common anode rows, please correct me if i am wrong
please someone help need to complete this and start another project
i used uc to 74154 to udn2981 to led to uln2003 to uc and nothing was glowing
then i tried uc to 4514 to udn2981 to led to uln2003 to uc and it worked in the same dim way as it was before
what now
edit: nevermind that i got the problem and if anyone who has same problem you can solve it by flashing the sequence for more time period for single sequence then move the sequence and again display it, try not to include delay when flashing and just keep flashing it continuously