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Sign with the letters filled with LEDs and diferent blinking(on) styles

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Alek

New Member
I need to design a sign for my school that will have the letters filled with LEDs. Every letter will be independent in managing and will have all LEDs in it in parallel (or serial if its a better solution).

Can someone suggests how can I turn on/off the letter ? Preferably with no relays, 'cos I plan to program the whole thing using multiplexing and produce different styles of blinking of the letters.

I'm thinking about some powerful NPN transistor (2N6290) that I will control with a microcontroller or with the output of a decoder.

The sign will have about 18 letters, and will be 2m by 50cm. I'm still designing the letters with the LEDs but there will be probably around 50/60 (maybe less) LEDs per letter.

Thanks in advance.
 

audioguru

Well-Known Member
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Ordinary LEDs have a max allowed current of 30mA and are used at 20mA or 25mA.
Some LEDs have a max allowed current of 1.5A (each) and are much brighter. I don't know which type you are using.

If you use 50 ordinary LEDs per letter then the total current is 1A to 1.25A.
A 2N6290 and nearly all power transistors need a base current of 125mA to switch 1.25A so you need a driver transistor in between the PIC and the power transistor, or use a logic-level Mosfet instead of the transistors.
 

audioguru

Well-Known Member
Most Helpful Member
An IRL3103 is a logic-level mosfet that switches on when its gate is 4.5V or more. It will be fine.
The resistor in series with the gate prevents the Mosfet from oscillation. Use 100 ohms if the Mosfet does not switch at a high frequency.
 

Alek

New Member
Thanks, I will present this to my professors tomorrow ... I don't think that anyone will have anything against this design.
 
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