Arduino Forum

Using Arduino => LEDs and Multiplexing => Topic started by: Passenger12 on Feb 17, 2017, 10:13 pm

Title: Shift register for simple 10x3 LED Array with Duty Cycle?
Post by: Passenger12 on Feb 17, 2017, 10:13 pm
Hello,

I currently have a 10x3 LED circuit that works great. The LED's are always on and they run off of a 12VDC power supply. Each 3-LED branch recieves 20mA (I'm using 20mA LED Drivers). However, now I want them all to blink simultaneously. I can use my UNO to program the LED's to blink at set Duty Cycle, but the ATMega328 obviously cannot meet the power requirements of my array (12V,200mA).

Is it possible to upload the sketch to an appropriate shift register and drop it into my circuit?


Thanks for reading. 
     
Title: Re: Shift register for simple 10x3 LED Array with Duty Cycle?
Post by: PaulRB on Feb 18, 2017, 09:16 am
(http://forum.arduino.cc/index.php?action=dlattach;topic=456527.0;attach=199777)

Your question does not make sense. You cannot upload a sketch to a shift register. A shift register is not a programmable chip.

What did you mean by "I'm using 20mA LED Drivers"?

To drive your array with Arduino, you need a transistor. A bc337 will be OK, with a 470R base resistor.

If you simply want to flash your array, you could use a 555 timer chip. You would still need a transistor for 200mA.
Title: Re: Shift register for simple 10x3 LED Array with Duty Cycle?
Post by: Passenger12 on Feb 19, 2017, 05:45 am
Great info, thank you.

As far as the drivers go, I'm just using them in place of resistors to supply a constant current to my branches.

Thanks for the direction.
Title: Re: Shift register for simple 10x3 LED Array with Duty Cycle?
Post by: PaulRB on Feb 19, 2017, 09:23 am
As far as the drivers go, I'm just using them in place of resistors to supply a constant current to my branches.
Not necessary in this circuit. Resistors will do fine. Constant current circuits are important when high current leds (e.g. 300mA per led) get hot and their forward voltage changes. CC circuits adapt to that change. But your leds will not get very warm at all, so their Vf will stay pretty constant.