Discussion in "Project Help" started by    iamalien    Mar 26, 2015.
Thu Mar 26 2015, 01:13 pm
#1
Hello guys, i am doing a project on display using 8051 on led matrix(which i made myself considering dot matrix is very pricey)(also i am going to extend the project to use a keyboard so that it will run be input from keyboard and output to led matrix, but for now i am doing the display part so as to check if it works properly).
I have tested the circuit using 8051 p1 to cd 4514 to udn2981 to common cathode columns then from anode row to uln2003 to p2 of 8051, and i am stuck at a problem that the led is always dim(as in i can see it only if i concentrate to look at the display), but the text is being displayed and scrolled as it should be, i have tried to test it by many different ways but of no use, please help me overcome this problem.
(it is to be noted that i am using 1 adapter for all 5v 1a rated but it shouldnt cause problem since i am not keeping all led on at once only flashing columns, but still please tell me if it can cause problem)
(please need a help bit fast since i need to complete the keyboard part too and take another project in hand )


[ Edited Thu Mar 26 2015, 01:14 pm ]
Fri Mar 27 2015, 02:33 am
#2
As you say, each column is only on for part of the time.
If an LED is only on for 1/8th of the time it will only be 1/8th as bright.
You have two options
1: Put a large current through the LED when it is on.
2: Use a design that keeps the LED on longer.

Post your circuit so we can see what you are doing.


[ Edited Fri Mar 27 2015, 02:41 am ]
 iamalien like this.
Sat Mar 28 2015, 09:57 am
#3
i thought that lighting led for more times should be causing the problem but dismissed it thinking that led is going on for a fraction of second, but after your post i thought how stupid i have been and am flashing the sequence 200 times and now i can see it properly, now i will just interface a keyboard and then no need of computer to put in the sequence of letters, after this i'll be doing equalizer like display on it(might put these projects here)...
just a last question, can i change the eeprom memory(or the program memory) when i am executing the program? or is only ram the one which can be changed(i get it that its rom but it is also electrically erasable so please tell if it is possible)


[ Edited Sat Mar 28 2015, 09:59 am ]
Mon Mar 30 2015, 12:49 am
#4
EEPROM can be changed at runtime. Program memory can also be changed at runtime but it depends if your controller provides IAP (In-Application Programming) abilities.

Let us know what eeprom and 8051 controller you're using in your project.
Mon Mar 30 2015, 12:55 am
#5
i am using at89s52 i guess it is only isp not iap, so i wont be able to change rom memory during runtime then?
Mon Mar 30 2015, 01:07 am
#6
Correct, you cannot change ROM, but you can still change eeprom. I am assuming you are using some kind of I2C EEPROM.
Mon Mar 30 2015, 01:16 am
#7
yes either that or use the flash reprogrammable varient of 8051 or if its ok to display ~200 characters then i will not need anything else since the 256 bytes ram takes care of that


[ Edited Mon Mar 30 2015, 01:16 am ]
Tue Mar 31 2015, 09:40 am
#8
256 bytes ram for 200 char display... I think you need a better controller or you may fall short of memory. Do consider ram required for local variables and stack.
Tue Mar 31 2015, 10:01 am
#9
i have already compiled the program in keil thats why i was saying somewhat near 200 was available for the data i could save and i have now made the algorithm such that i would need only 1 byte to display 1 character
 ElectronicManiac like this.
Tue Mar 31 2015, 10:03 am
#10
Can you post Keil compiler output?

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