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Topic: Control 24 led with multiple 74hc595 (Read 3479 times) previous topic - next topic

lorenzo_r

Nov 19, 2013, 08:42 pm Last Edit: Nov 19, 2013, 08:46 pm by lorenzo_r Reason: 1
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
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

nickgammon

Are you not using hardware SPI? If not, why not? SCK normally comes from D13, not D12.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

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.

Quote
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.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

nickgammon

You should have decoupling capacitors.

http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

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.
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Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

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