Making the jump from USB Power to External

noob questions again.

i building 6 led modules controlled by  74hc595 shift registers daisy chained. 1 shift register on each module. modules in straight line. want power whole project 12v external battery. since driving leds has been recommended me use tpic6a595s current rating.

to avoid frying anything, best way this? want individually control each led want them powered external power source , not getting regulated down 5v arduino. current wiring schematics tutorials shiftout. feel should have transistors somewhere?

i feel cant simple swapping in tpics , having more current through because itd still going through ardunio first correct? want arduino signal.

i have code required run on basic 595s, hardware clueless.

quote

i feel should have transistors somewhere?

the tpic6x595 provide transistors. these 74hc595 open-drain outputs added, designed sink current high voltage sources.
for example, offer board uses tpic6b595 sink current thru led strips powered 12v. each led needs current limiting resistor, of value (vsource - vfled)/current  = resistor ohms. 12v, single red led vf of 2.2v, , 20ma (0.02a), r = 490 ohm.
make sure have 0.1uf cap on vcc pin of each shift register, , not on signal lines.
http://www.crossroadsfencing.com/bobuinorev17/

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