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Topic: daisy chaining 74HC595's (Read 2 times) previous topic - next topic


Feb 13, 2013, 05:14 pm Last Edit: Feb 13, 2013, 05:24 pm by Ruffsta Reason: 1
most of my projects will involve ATLEAST 100 leds - (some 50)... whether they be single color, bi-color or RGB - (most are RGB), but i have a few projects that are single color..

right now for this specific project, i have a sheet of pegboard - it will hold 1,012 RGB leds.. so,  1 uF capacitor for every 74HC595 and 1 pnp for every 10 leds is what i'm told...

i may do the same project using just blue leds, but for that i can use max7219's - as each one can drive 64 leds - requiring less than the one with RGB leds.... may even try one with bi-color leds.. haven't decided if i want to build a third project of it.. but the RGB one and the single color one - i am interested in doing right now.

Runaway Pancake

Feb 13, 2013, 05:37 pm Last Edit: Feb 13, 2013, 05:40 pm by Runaway Pancake Reason: 1

.. so,  1 uF capacitor for every 74HC595 and 1 pnp for every 10 leds is what i'm told...

Oh ? ? ?
So, who's The Authority?

... i am a chef by trade!

How many cloves of garlic does chicken get cooked with?
How much baking powder should I use with flour?

Catch my drift?
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"


Feb 13, 2013, 06:52 pm Last Edit: Feb 13, 2013, 07:01 pm by Ruffsta Reason: 1
Quote from: Runaway Pancake

Oh ? ? ?
So, who's The Authority?

if you must know... CrossRoads... mod and 22 yr engineer on here...

Quote from: Runaway Pancake

How many cloves of garlic does chicken get cooked with?
How much baking powder should I use with flour?

Catch my drift?

depends on what kind of chicken dinner/lunch you are making.. but atleast i was being specific on my project!

here we go again with the sarcasm...

k, i'm taking a break from arduino and the bs sarcasm... it's really starting to piss me off and i don't need anyone's crap anymore

anyways, thanks for not making me feel welcome on this forum everyone.. wish i could say it was a blast.. but i won't lie, it wasn't thanks to all the bs sarcasm that has been dished out to me more than once.. i hope this isn't how you treat all new people to arduino and the forum.


starting to feel sorry i bought this damn thing for my son and i to have something to do together and joining this forum.. since day 1 i never felt welcomed here... and i still feel the same way. glad i won't let my son join this forum... i can imagine how he would be treated.

and for all of you "experts" on here.. shame on you for not remembering what it was like being new and/or not having the patience to those that are new.. and you should also stop talking to all the new people like they know as much as you.

Maybe you've been disappointed because you're so hostile.  There's a LOT to learn when getting into electronics.  You can't just go to the forums and demand that someone show you how to do things.  When the first poster suggested checking the datasheets you got mad.  But that's step 1 when using ANY new component.  You ALWAYS start by looking up the datasheet, as it's filled with info that will help you use their product properly.  All you have to do is look at the part number. 

74HC595 is a type of IC made by lots of manufacturers, but they all have their own unique part number.  For example, the ones I got from TI are SN74HC595N.  By looking up that datasheet, I found that the maximum current it can handle is 50ma.  If you use 180 ohm resistors as shown in the image in the OP, lighting up more than 3 rows of lights will fry the chip.  And that's with a PNP transistor switching their current.  Just the gate current drawn by the transistors will put you over the top.

So try not to get frustrated.  There's a lot to learn, but all it really takes is a bit of research.  Engineers spend years learning this stuff in college.  Don't be afraid to spend an hour with your nose buried in a datasheet.  You'll be a lot more successful and things will make a lot more sense when you come back to the project armed with knowledge about how it works and why each component is needed.

Also, the first image that you posted leaves the output enable pin floating.  That's not good.  But you'd know that if you had read the datasheet.   8)


Ruffsta is actually referring to a 0.1uF cap that will go on the VCC pin of every 74HC595.

TI is the authority:
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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