Go Down

Topic: 900 Led controller (Read 1 time) previous topic - next topic

manteliukasx

Hi! i want to ask is any chip which supports arduino, have atleast 10output pins and 5input pins, also each can be loaded 500mA or more?
I want to make big project with led multiplexing, so my arduino one pin can load only 2 leds with 20mA current, but i need 25-30 leds in row to control. Also i think i could make 5bit combiter with bc547 transistors to use lesser pins. Please help me and leave advice :)

Grumpy_Mike

Quote
is any chip which supports arduino, have atleast 10output pins and 5input pins,

Yes there are lots.
One option is shift registers:-
http://www.elcojacobs.com/shiftpwm/

Quote
also each can be loaded 500mA or more?

No there are none that include his function.
To do this you have to add external FETs to the logic outputs of the expander chip.

Quote
leave advice

Forget 900 LEDs until you know a lot more than you do at the moment. Electronics do not scale up to this sort of size very easily.

manteliukasx

Quote
To do this you have to add external FETs to the logic outputs of the expander chip.

Can you explain about external FETs?

Boffin1

I use  TPIC6B595 shift registers to latch the high current outputs for long strings of LEDs , it can stand 50 volts )  Some of my projects use 2500 LEDs.

You would have to split the LED strings to have 150mA per pin  (  they can be daisychained and just use 3 pins of the Arduino )
With my mobile phone I can call people and talk to them -  how smart can you get ?

manteliukasx

Now i understand! that 5bit computer which i mean is shift register... Whats why in led cubes sets transistors, its like shift registers.. Thanks you. One more question, do you know any shift register which can load atlest 500mA current or more?

dc42

I don't think you will find a shift register with 500mA outputs. I suggest a regular 74HC595 with each output driving a mosfet or super-beta transistor through a series resistor.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

funkyguy4000

if you need to source 500mA but insist on using 74HC595 shift registers, you can use the UDN2981AT.  Its capable of sourcing your 500mA needed. 
Here is a video that covers the concepts extremely well.  You may or may not be using a dot-matrix display, but this guy is using the 595 and 2981A
Watch it, trust me, it'll help.

http://www.youtube.com/watch?v=wXvs0CrRPIw&list=FLfjRGtXoqzGDd_e_d6GS0TQ&index=1&feature=plpp_video
Accelerate to 88 miles per hour.

manteliukasx

Thanks you guys very very much. :)

dc42


if you need to source 500mA but insist on using 74HC595 shift registers, you can use the UDN2981AT.  Its capable of sourcing your 500mA needed. 


500mA is the absolute maximum output current of the UDN2981. The recommended maximum is 350mA, and at that current the voltage drop is 1.8V typical, 2.0V maximum. If you drive just 3 of the 8 outputs simultaneously at 350mA, you will already be close to the device maximum power dissipation. So I advise against using the UDN2981 in this application.

The ULN2803 current sinking driver is slightly better, with voltage drop 1.1V typical, 1.6V maximum at 350mA.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

manteliukasx

Can i use bc337 tranzistors instead supply drivers and with shift registers controll them?

dc42

BC337 performance is marginal in this situation. ZTX851 would be better, with a 4K7 base drive resistor (any lower and you will exceed the 70mA total current rating of the 74HC595).
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

packocrayons

Darlington arrays would be the best way to drive 500ma. What you could do is if you're concerned about overloading it, run half the led's on on darlington and half on another. I use them at near 400ma per pin, I haven't done it for a long period of time but it doesn't heat up at all in about 30 seconds, especially if they're off more than on.

manteliukasx

Maybe you have any advice to controll each led(or each row) resistance with arduino? what components i will need for that?

Grumpy_Mike

The shiftPWM does not use multiplexing but it requires a lot of refreshing to maintain the brightness level of the LED.
Do you need to control the brightness or are you going to just control on and off?
Controlling brightness AND multiplexing a matrix is possible but even more CPU intensive.
This is what you need to do for a multiplexed matrix.
http://www.thebox.myzen.co.uk/Workshop/LED_Matrix.html

manteliukasx

yes, im going to control each led brightness and also make matrix

Go Up