Hi, I am currently trying to design a project which uses 96 individual LED bulbs (2V forward voltage, 20 mA). I want to be able to address each individual bulb so I am planning to use 10 74HC595 shift registers daisy chained together to achieve the amount of I/O pins needed. I plan to have all 96 in parallel with each other as well as each LED being in series to a 150 ohm resistor. Can the Arduino power this set up and will this even work the way I am intending it to?
In a worst case scenario where all of the LEDs are lit, 96 LEDs * .02 amps = 1.92 amps. You don't want to exceed .5 amps with the Arduino's power regulator, but you can certainly use an external power supply to power the LEDs. That just requires connecting the Vin/GND of each of the 74HC595s to that additional power supply and then additional link between the supply's GND and the Arduino GND.
Thank you for responding so quickly, do the specs of the external power supply matter or is any one fine as long as it has enough current to power the LEDs and I adjust my resistors properly for the voltage?
You can use 2 x max7219 chips instead of the 10 x 74hc595. This will save you many components and make your circuit much more simple. It will also use less current so that you may not need an external power supply.
Also 74HC595 has maximum Vcc or GND current 70 mA so you cannot provide 20mA to more than 3.5 LEDs via one chip at the same moment.