help on dot matrix display..

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cuber18

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im task to build a 14rows and 40columns led matrix.. as of now i have build a 10x40 led matrix display.. what should i do? im using 74hc595 in my columnss and 74ls154 in my rows with tip147.. and my scroll should be scroll to right and left.. and in static mode.. and also do some blinking.. anyone have a code for this scroll? btw im using pic16f877a microcontroller.. this is a two liner led matrix.. how can i input characters from first line and another different message in the second line? i really need some help because im new to this..
 

Hey i wonder how it would be done! well i m not that expert but this link might help you.
h**p://www.avrprojects.net/index.php?option=com_content&view=article&id=79:dot-matrix-scrolling-led&catid=38:avr-projects-with-leds&Itemid=58

---------- Post added at 21:17 ---------- Previous post was at 21:15 ----------

another one
https://www.edaboard.com/threads/157348/
 
thank you for the reply sir.. im not using assembly in my programming btw, i want a mikroC programming for this project..
 

sir, i have constructed a led matrix w/c rows is negative and columns is positive.. if i will connect a pnp transitor on my rows whats the connectioN?
 

Hi,

You may simply connect base of pnp transistor to signal line through a resister. To turn on transistor you may pull-down that signal line.

Selection of transistor and resistor depends on connected number of LEDs and their requriement of current and voltage (also the supply voltage).

Thank you,
 

whats that again sir? my base to the output of my 74l154 and my collector to the row of my matrix? and emitter to the ground?
 

Hi cuber18,

I guess you use 5V supply;

You can connect output of 74LS154 to your pnp transistor's (eg 2N3906) base through 4.7K resister. Since you use pnp (for rows), you have to connect emitter to +Ve (not the ground). Then connect collector to LED-anode through 1K resister. (then LED cathode to -Ve directly)

Hope this solve your problem, thanks,
 

**broken link removed**

i have thiz as my reference.. i think the row is in cathode and the column is in anode.. and he said that in reality in a common anode i have to connect PNP tranziztor.. so when i connect a tranziztor to the row, the display is broken..
 
Hi,

According to above diagram LED block should have "common cathode" along a row; (since 74LS138 select the line by grounding). But in reality you have "common anode" LED block along a row, and you connected PNP transistor for those rows.
Also you replaced 74LS138 with 74LS154. Am I correct ?

Then how you connect other pin of LED block; is it directly to 74hc595 like in above schematic ?

(If you can post your modified schematic, it will be easy.)

Thank you,
 
so in reality my row is cathode and my column in anode? yes your right im replacing that 74ls138 to 74ls154.. i dont have any modified schematic.. that is my only reference to build my own led matrix.. thats why i need professional help on you guys..
 

Hi,

Ok,
7 LEDs Column is anode : you use 74HC595 as on schematic, it out "high" (+ve) to turn on LED

5 LEDs row is cathode : You can use 74 LS138 as a replacement for 74ls154. It out "Low" (-ve) to turn on LED

So no need of transistors. However you should able to connect pins of LED in matrix as "5 LEDs row is cathode" and "7 LEDs Column is anode". Is this possible in your LED matrix ?

Thank you,
 

you mean 5 led Column is anode and 7 led row is cathode? i never tested it in actual thats why i need some advice.. and im applying it to 14x40 led matrix with 14 rows and 40 columns..
 

Hi,

You can increase row,columns up to 14 rows-cathode and 40 columns-anode.

In your schematic it has 7 row and 40 columns, so you only need to double the rows. Hence you need one more 74 LS138 to control them.

Thank you,
 
thank you for the reply sir now im confident about my circuit.. thank you..
 

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