help making a nightlight please

Hello,

I picked up an arduino uno a couple days ago and could use some help with my project..

I basically need to have 3 groups of LEDs doing different things...

Group 1 and 2 are stars and a back lit horse I just need some white LEDs to stay lit all the time, this I have figured out as far as programming goes but Im not sure how to wire 20-30 LEDs with limited I/O pins.

Group 3 is for fireflies and I just need 4-6 yellow LEDs to fade in and out...

Programming it all I have covered but wiring it is throwing me off and im not sure where to start or what to look for...

I have: 5mm white LEDs 25mA 3.3 5mm Yellow LEDs 20-30mA 3.0v 74hc595 shift register x1

Thank you in advance for any help.

wire 20-30 LEDs with limited I/O pins

I have:
5mm white LEDs 25mA 3.3
5mm Yellow LEDs 20-30mA 3.0v

If you are going to get more LEDs, consider “neopixel” (from adafruit or others). A chain of them could be controlled by only one pin.

The LEDs that are on all the time don't have to be connected to I/O pins unless they'll be turned on & off by the Arduino.

If they do need to be controlled, they can all be controlled by one I/O pin, but they can't all be directly powered by one I/O pin. You'd need a transistor or MOSFET to boost the current.

The Arduino I/O pins are rated for 40mA maximum (about 2 LEDs maximum per pin) and a total I/O current of 200mA. (i.e. You can't get 40MA from all output pins at the same time without potential damage to the Arduino.)

Group 3 is for fireflies and I just need 4-6 yellow LEDs to fade in and out...

You can use PWM to fade LEDs. Again if they all fade together, you can use one I/O pin and a transistor/MOSFET to boost the available drive current. If they need to be controlled/faded independently, each one needs it's own PWM output.

I don't think you need the shift register... With shift registers, 3 I/O pins can independently address/control an unlimited number of LEDs (you can daisy-chain shift registers) but you can't independently dim LEDs with a shift register.

...20 or 30 LEDs at an average of 25mA may be too bright for a night light. You may need to cut-down the current (by using higher-value current-limiting resistors).

DVDdoug: ...20 or 30 LEDs at an average of 25mA may be too bright for a night light. You may need to cut-down the current (by using higher-value current-limiting resistors).

the light from the 20-30 LEDs are only going to be visible through small holes so they wont be too bright... I may be able to get away with using less as long as the light is visible..