Control 24 led with multiple 74hc595

[lorenzo_r]

Hi i'm currently planning to do a small project for christmas.
I want to switch on/off specific LEDs (They all can be on at the same time) based on the ds1307 hour.

I have to control approximately 24 led with 3x 74hc595.

This is my schematic
Full screen
http://i39.tinypic.com/154kew0.jpg



I use a second usb power (2.1A max) as power source for the leds and the three 74hc595.

I wonder if it's all right or i have done something wrong. Just to be sure.

Thanks  

[nickgammon]

These Fritzing diagrams are not easy to follow. Do you mind posting a proper schematic?

In case it helps, I have a page about 595s, I had 32 of them in one setup.

http://www.gammon.com.au/forum/?id=11518

[nickgammon]

Are you not using hardware SPI? If not, why not? SCK normally comes from D13, not D12.

[lorenzo_r]

Thanks for your reply!
I have done a better schematic
http://i44.tinypic.com/2i23jnm.png

I don't know what spi is. I'm a student and i'm still learning these things. This is my first serious project.

I looked at your link and i wonder if i really need to use a external usb power supply to control those leds. I read arduino maximum current is 200mA i think it's not enough

[nickgammon]

http://www.gammon.com.au/spi

Read my link above about controlling the LEDs using SPI.

I looked at your link and i wonder if i really need to use a external usb power supply to control those leds. I read arduino maximum current is 200mA i think it's not enough

I had 32 LEDs from 4 x 595s in my project. A lot would depend in your current-limiting resistors, which I trust you have.

[nickgammon]

You should have decoupling capacitors.

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

[CrossRoads]

24 LEDs with 8mA thru each (the most you should put thru an 74HC595 pin assuming 8 can be on) will require 8x24 = 192mA. The Ardiuno can power that, from USB, or from the 5V regulator, assuming you have say a 7.5V power source feeding the barrel jack.
http://www.dipmicro.com/store/DCA-07510