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Hello,
I am new to this forum so i hope that you can help me out guys.
I tried to find but i couldnt, informations about how many shift registers (595) you can attach to 3 pins on arduino, i found only examples for 2 registers, and i was wondering how many outputs can i get... what i am trying to do is, to control through serial, light bulbs making a big screen of them(and play a pong on it or something smiley ), and switch them on and off using a transmiter that closes cuircuit on +5V (logical 1) and opens on 0V, it is a simple electromagnetic switch. I figured out how to control 80 bulbs with 2 registers on each 3 pins, so i could get 80 bulbs. I was also thinking about Max7129 but it works fine only with led matrixes because it refreshes in about 50Hz so human eye can't see that at the moment not all led's are blinking, but in this situation i need to keep the 5V all the time if i want to make the bulb light...

thanks for any help!
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You can connect as many 74HC595 chips as you want!  But you will run into limitations due to complexity, power consumption and slow operation if you have very many chips connected.  Remember that all the devices (LEDs, relays, light bulbs, whatever) will consume current when switched on, and that current will add up!  Plus, with a bit-serial interface, it will take more time for each chip (8 bits) that you add to the system.
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i wanted to supply current to those chips outside of arduino, from power supplier. How  big delay would it be with 4 595 chips on 3 pins??, because this  transmiter switche have about 10ms delay before they switch on so maybe little bit more delay would not make difference?.
« Last Edit: March 03, 2009, 04:04:00 pm by azjata » Logged

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with 4 shiftregisters the delay will be very short, i can't say exactly how short, but very short.
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that's good, do i need an extra capacitor to handle the second pair of registers?
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to admin: sorry could you move this topic to hardware:interferencing, i made a mistake making it here

thx
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do i need an extra capacitor to handle the second pair of registers?

If you're talking about decoupling capacitors on the power supply, then yes.  You should fit one decoupling capacitor for every two chips, and lay them out close to the chips themselves.
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Thanks a lot, i figured how to connect 4 registers, i wrote a small app in c# that controlls all the leds, later to support displaying jpeg sequence animations. later on i will replace the leds with transmiters.
I will upload my progress on this 15x15 bulb screen...
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You can connect as many 74HC595 chips as you want!  But you will run into limitations due to complexity, power consumption and slow operation if you have very many chips connected.  Remember that all the devices (LEDs, relays, light bulbs, whatever) will consume current when switched on, and that current will add up!  Plus, with a bit-serial interface, it will take more time for each chip (8 bits) that you add to the system.

On power consumption, I'm worried about drawing too much from the 74hc595. I see that its specs (At least for the one from Fairchild sold by Futurlec) are ±35mA per pin, but "DC VCC or GND Current, per pin (ICC)" is ±70mA. Does this mean I'm limited to a total of 70mA on all output pins, or just under 10mA per pin if all are lighting an LED? The 600mW power dissipation suggests I should be able to run 15mA per pin at 5V.

Sorry if this is a really noob question, but I don't want to go and fry a bunch of chips, and this is all really confusing.
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Does this mean I'm limited to a total of 70mA on all output pins

Yes, with those chips, it looks like you are limited to 70mA in total.  As you say, just under 10mA per LED pin.
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Yes, with those chips, it looks like you are limited to 70mA in total.  As you say, just under 10mA per LED pin.

Thanks. I tried out some LEDs I had at low currents, and was rather surprised. They can light up pretty well at single-digit milliamps (Got them down to 3.3mA and they lit up almost as bright as at 10mA. There was a noticeable difference at 1mA though). I'm more used to driving them as hard as they can take rather than only as much as needed. smiley

I love your pictures in the Make: pool on Flickr BTW!
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Sounds like you'll be able to run the LEDs at, say about 9mA and stay under the 70mA limit.

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I love your pictures in the Make: pool on Flickr BTW!

Thanks!
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hello,
I become very worried, after the last 3 posts, i will use these transmiters(http://www.laro.com.pl/pdf/hm4100f-5v.pdf) and these 595 ( http://www.nxp.com/acrobat_download/datasheets/74HC_HCT595_4.pdf ) and I started to worry if 595 will handle 8 of these transmiters, can somebody help me out and check if it will switch, with 1 transmiter( because i have only one at the moment ) and 7 leds, it works perfectly with no problems, but i am worried if 10mA will be enough? if not, can i use a capacitor to help it to switch? or it will flicker on/off, when capacitor is loading and releasing the current? please help we have only 2 days to finish this project...

THANKS!!

btw. my transmitter has H in the name so it's 200mW
« Last Edit: March 08, 2009, 05:50:38 pm by azjata » Logged

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azi,

what's most common for relays running off of ICs, due to their high current demands, is to use a transistor to switch the coil. I have never done this, but this page http://www.kpsec.freeuk.com/trancirc.htm seems to have a lot of good info on how to set up a chip and transistor to operate a relay. Note that you'll need a diode, too, to deal with the EMF stored in the coil when you turn it back off.

Sorry I can't be of more help, but perhaps that page can tell you what you need to know in time.
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Its probably too late, since you said you only have 2 days left, but I've had good luck with the M5451 chip, which does 35 constant current switches each.  Each chip can handle 1 watt total so that sounds like it might meet your power requirements.  Actually, you could probably put a heat sink on the chip to drive it even higher :-).  

See my blog:
http://effluviaofascatteredmind.blogspot.com/2009/02/arduino-and-m5451-control-35-leds.html

and also a conversation in exhibition:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1235795499
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