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Author Topic: daisy chaining 74HC595's  (Read 2215 times)
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ok, we all know i'm new.. so, excuse my lack of understanding this..

but according to:http://bildr.org/2011/02/74hc595/

the way they are daisy chaining them show 2 different ways.. both are using 2 74HC595's


and


the reason i am more aggravated than anything is... you get told different things by different people and when you look at tutorials - (not that youtube is good for any of that.. it's more like "look what i did" than actually teaching you something), people do it differently...


i just want to daisy chain as many as i want/need properly.. so can someone please explain (and show if possible) the right way of doing it as far as pnp's and capacitors go.. this is very important to me because most of my projects will revolve around this - (unfortunately because most of my projects involve using a lot of leds).

thank you
« Last Edit: February 13, 2013, 09:22:52 am by Ruffsta » Logged

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never mind, i get it... but where does uF capacitors go? i thought you needed 1 for every 74HC595? also, they may not be using 10 leds... but i'd like to know where the pnp goes as well (because i will be using 10 leds per row in a lot of my stuff)..
« Last Edit: February 13, 2013, 08:32:11 am by Ruffsta » Logged

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I would go to the MANUFACTURERS data sheets for the correct method - and then upload your own youtube vid smiley-wink
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that's not very helpful.. i have 74HC595's from different sources.. i don't know who the actual manufactures are nor am i going to track them down... (like i don't have other things to do)... and honestly, i don't know your skill level, but i'm not going to take advice from someone new who has less posts than i do.. no punt intended.
« Last Edit: February 13, 2013, 08:25:44 am by Ruffsta » Logged

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Those two schematics appear to show the same thing to me.

The first one just shows how the signalling wires are connected,    the power and ground wires and leds are omitted.
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yeah, i got it.. refer back to my second post..
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Well... It's probably the best advice you can have, and I (used) to design for a living, I just do it for fun now; what about you?

ALWAYS go to the manufacturer because many manufacturers have to produce variants to get around patents or to give their product an edge.

What you are really asking, and why you are poopooing the youtube video, it to have the design handed to you on a platter!

The manufacturer will provide you with ALL the information that you need.

Admin, can you please bump up my post rate, it's too low for some people. TY
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look, i'm getting sick of everyone's sarcasm around here! i'm not asking for anything to be handed to me on a silver platter.. i just want to know where the freaking pnp's and capacitors go! that's all i'm asking for!!! damn..

as for me, i have made ds games, pc games/software and websites, i have also owned an online mafia game, i'm mod on a gardening forum, i have done tons of security work and getting into armed security - i am a chef by trade! so good to all of us for having a past!

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.
« Last Edit: February 13, 2013, 09:17:07 am by Ruffsta » Logged

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With regard to decoupling capacitor placement - one lead should be connected to pin 16 and the other lead should go to directly to Ground (the Ground bus itself, as opposed to going to some point that's connected to another point that's jumpered to Ground.)

OK?

> > >
The board that I made for this display



uses 9 '595s - none of which gets "decoupled".
(There is one 1uF across +5/supply on the board.)
Rarely will anything on this level flop for lack of adequate decoupling.
« Last Edit: February 13, 2013, 10:53:35 am by Runaway Pancake » Logged

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never mind, i get it... but where does uF capacitors go? i thought you needed 1 for every 74HC595? also, they may not be using 10 leds... but i'd like to know where the pnp goes as well (because i will be using 10 leds per row in a lot of my stuff)..

You need a decoupling capacitor (0.1uF usually) as close as possible to the power leads of every chip.  Its perfectly possible to share
one between two neighbouring chips, if they are adjacent, the important thing is that the leads between the chip's supply pins and
the capacitor are short...  The purpose of the capacitor is to stop the voltage dropping as currents switch on a time scale of a few ns to us,
it far faster than the power supply can adapt to load changes.

With lots of LEDs the currents being switched are larger and extra decoupling capacitors (10uF or so) are probably a good thing -
these don't have to be as close to the chips as they handle a somewhat longer timescale.  Adding a few might be needed.

You mention PNP transistors - are you planning a multiplexed array?  Are you commoning the anodes then?
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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.
« Last Edit: February 13, 2013, 11:24:00 am by Ruffsta » Logged

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.. 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?
« Last Edit: February 13, 2013, 11:40:16 am by Runaway Pancake » Logged

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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.
« Last Edit: February 13, 2013, 01:01:09 pm by Ruffsta » Logged

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

TI is the authority:
http://processors.wiki.ti.com/index.php/General_hardware_design/BGA_PCB_design/BGA_decoupling
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