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how to design a 14x40 led matrix

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cuber18

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i want my led matrix in rows to be in cathode and columns in cathode? what appropriate transistors should i use in my columns and in my rows? if i use 74ls154 in my rows what transistors will use.. and in my columns 74hc595?
 

Sooo... rows are cathodes or anodes? Let' start from this point
 

my rows are cathode and column i anode sir takeshi..
 

cascade the 74hc595 shift registers for columns, try to calculate the full current for one column ie. 14 leds it will depend on the brightness required, that will help to select the transistor. it is possible to reduce the current further by using pwm.

ask for further help if required. :)

helpful?
 
how can i calculate about the pwm of the leds? same thing about the rows? i will calculate it also?
 

first calculate for using without pwm. it will be better if you first have the display working ;-)

to calculate just connect a ammeter in series with your led column. this will give you a rough idea of the current required.

note: make sure all leds are glowing.

then adding pwm will be easy with relatively few changes.

Helpful? Please click: Yes
 
sorry can you orient me about what is pwm mean?
 

theta how about "no".
And how about use octal->binary decoders for columns(sorry 6 ICs) and 2*7 drivers for rows?
In this case you will have maximum 14 LEDs "on" at each time-slot, so current will be 100-200mA depends on LED
 
Last edited:

i want my pnp transistor to sink current.. can i sink the current if my pnp's base in active low and my emitter to gnd, and my collector connected to cathode of my matrix?
 

collector to GND for pnp transistor, emitter to LEDs, don't forget resistor in the base circuit and current limiting resistors in anodes.
Also some octal-to-binary decoders have "open collector" output, which is "low" when active, so you can "sink current" with less components.
So in total
cathodes are columns, 14 LEDs in each column
anodes are rows, 40 LEDs in each row
at one time-slot you can light one column with 14 LEDs
by applying code to decoders, you will choose which column you will "turn ON"
by applying code to drivers, you will "turn ON" LEDs in column with active "1"

one more hint - if you want to save I/O lines of controller, you can drive decoders with counter, so you will need just one I/O instead of 6, but it depend what sort of MPU you will use
 
thank you sir.. what safe resistor could i use for my base, emitter and collector? :) my only problem is controlling it... thank you
 

in base, say 4.7kOm(40 of them for your columns and 40 transistors with Ic max>350mA)
in emitter you don't need one - you will have them on other side of your matrix in anodes
and in anodes - it depends on your LEDs and driving voltage. if you will drive your matrix with 5V, resistors will be 300-560Om(5V/InormLED and you need 14 of them)
if you are not sure about resistor, lets connect in serial 2 by 330Om, then if brightness not enough, shortcut one resistor in each row.
You will have only 14 extra resistors and the are not so expensive
 
ahhmm i dont get it.. heheh! :p

my base is 4.7k? and my collector i how much? my collector is connected to my negative row... and how about the 74hc595? what resistor should i use?
 

yeah i saw this one.. but im using 74hc138 and pnp transistor in my rows.. hhehe :) sir teach me how to calculate the resistance for my pnp transistor..
 

cuber18 said:
sorry can you orient me about what is pwm mean?
Click to expand...

pwm is pulse width modulation..and you dont need to bother your self to measure the leds with the pwm....simple leds can be measured using the multimeter...so dont be confused about the pwm...
 

hehehe.. yeah i know about pwm.. but i dont know the relation of pwm to led matrix.. heheh :) maybe i have many to know about electronics..
 

in my design is all the source and gnd the same? and what supply should i use?5v or 9v?
 

i have a ac supply with 1.2A.. is it enough for both pic and 595? and whats the output current of PIC? can it accommodate the total current of 5 595? and another supply for my transistors?
 

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