hi, im working on a simple 8x8 LED matrix. the 74HC595 seems like a pretty popular package, it goods enough for simple applications and can source and sink current. ive been reading for a few hours today about LED matrices:
also, this IC is pretty lame on current ability(75ma max, +/-6ma per out pin). what is another arduino compatible, High current, PWM enabled(to dim LEDS), and can both source+sink current? if this doesn't exist whats the easiest way to still use ~3 arduino pins.
i don't think what i want exists, instead i would need a TLC5940 for sinking and then a MIC2981 for sourcing. but, the TLC5940 can be daisy chained and the MIC cant. could i use a 74HC595 to reduce the number of arduino pins the MIC uses?
The ULN2003 provides the necessary current to the matrix (presumably from an external power source) because the arduino does not have the capability to power that many LEDs.
could i use a 74HC595 to reduce the number of arduino pins the MIC uses?
I used 6 TLC5940's for my stairs project. I have grown fond of these controllers. They offer so much capability for the price. I've bought 20 of them off eBay for a very good price.
I could have used 3 and multiplexed but I wanted to ensure the every LED had the most current available to it.
They are working great!
I started the project trying to use AS1107's but couldn't get it stable with RGB LEDs. They source and sink current and have digital and analog brightness control. I will be using them on a LED matrix in the near future.
If you are willing to wait a bit, look to eBay for your LED needs as well. I've bought common anode diffused, common cathode diffused and common anode non-diffused RGB LEDs from there as well as 1000 blue LEDs. As a matter of fact, I've spent about $1000 over the past two months on eBay buying stuff mostly from overseas. LOL. I'm new to this hobby and have gone overboard like I do with my other hobbies.
Set them up like this. Arduino can drive Anodes high directly, or drive from 74HC595 if need to save a few pins.
NPN transistors can be be replaced with ULN2803, on output of Arduino pins, or from 74HC595.
Or use this http://www.ti.com/lit/ds/symlink/tpic6595.pdf Shift register with high current sink capability.
that was my first time buying LEDs, and i was going more for status LEDs not light shows(like i am now). but i did get some RGB LEDs (3 of them for testing) that are ~750mcd with same 20ma. thanks for the link, i guess digikey isn't so great(.5 vs .16 cents)
would the tpic6595 replace both the uln2003 and the 74HC595 for sinking current?
crap! i just realized that my RGB LEDs are only 3.3v, 1.9v and i put 5v into them... :D. They're not broke, but where can i get bulk RGB LEDs for cheap? i cant find any, and what about the voltage, are their any that use 5v instead of 3.3 or 1.9v etc? or do i have power them individually(each color)?
You need a current limit resistor on the unique cathodes (for a common anode part) or on the unique anodes (for a common cathode part).
Or use a part like TLC5940, 16 outputs, so can control 5 common anode RGB LEDs, plus 1/3 of another, and has built in current limiting so no resistors are needed.
"Did you put 5V across them with ground on the other side?"
nah i had resistors, so i think im good. they were random values from 220ohm to 330 ohm, as i didn't take the time to separate them from the bag.
"How'd you jump from simple 8x8 matrix to needing RGB LEDs?"
im eventually planning on using GRB LEDs and i just plugged in the 3 RGB that i had to test them.
"The ULN2003 provides the necessary current to the matrix (presumably from an external power source) because the arduino does not have the capability to power that many LEDs."
so i wouldnt have to use the uln2803 if i used a 5v 10A computer PSU to power the whole setup?
I've had good experience buying RGB LEDs from eBay. If you buy in bulk you can get good prices. For example, I was able to buy 200 7000mcd RGBs for $30 (they list the price as about $5, and then pull $25 from you for shipping). Comes out to about .15 per part. If youre willing to wait around a couple weeks for shipping id say that's definitely the cheapest option.
