chips & leds

can anyone please tell me the following:

1.) how many single leds can you control with 1 chip and which chip?
2.) how many bi-color leds can you control with 1 chip and which chip?
3.) how many RGB leds can you control with 1 chip and which?

i'm having a hard time understanding these because my arduino projects vary and i would like to know in which direction to go when i decide which project i am doing.

some projects will have 50 leds, some will have 100 and some can even reach 500 leds.. if i know which chip can handle what i'll know how to go about assembly. the other issue i am having is resistors. i have heard you can use less of them at times. and the stuff that really confuses me is stuff like PNP and NPN.

i assure you, none of my projects will have less than 25 leds and i am way to new to ever use more than 1,000. i am more of a games kinda person.. IE: keno, bingo, powerball.. so, this is where i want to focus on - just to give a reason as to why i need to now the above.

it all depends on what i want to accomplish - the type of led is usually bi-color or RGB. a single color really gets boring for any project when using a lot of them in a single project.

thank you very much

There isn't a one-size-fits-all answer to this, because it depends on how the LEDs are wired, i.e. direct to the MCU, multiplexed, charlieplexed, some RGB types have their own built-in driver chips that are daisy-chained or bussed, etc. etc. etc.

The best approach for any given project will depend. On not only the number of LEDs, but on things like refresh rates.

Given that you are talking about large numbers of LEDs, I'd say some sort of multiplexing is in order, so I'd be researching external chips that can help with that. You should also be comfortable with using (and calculating values of) resistors to limit LED current, and the application of transistors as drivers. Although multiplexing chips can greatly reduce or eliminate the need for these, there are still basic principles that need to be understood regardless of the particular drive circuitry.

1.) how many single leds can you control with 1 chip and which chip?

It is the same answer to the how long is a piece of string question. The MAX6954 can control 128 LEDs but you might not like the price.

2.) how many bi-color leds can you control with 1 chip and which chip?

Half the number of "normal" LEDs so 64 with the MAX6954.

3.) how many RGB leds can you control with 1 chip and which?

Guess what one third the number of normal LEDs. However there are three types of RGB LED, common anode, common cathode and separate anode and cathode.

i'm having a hard time understanding these because my arduino projects vary

In the same way as I am having a hard time answering this very woolly question.

the other issue i am having is resistors. i have heard you can use less of them at times.

Depends on the chip, some chips like the TLC5940 and the MBI5168 and many others have a constant current drive in the and so need no resistors with the LEDs at all.

it all depends on what i want to accomplish

Indeed it does, when you have that nailed you can start to ask sensible questions.

cupstacker:
can anyone please tell me the following:

1.) how many single leds can you control with 1 chip and which chip?

How long is a piece of string?

cupstacker:
2.) how many bi-color leds can you control with 1 chip and which chip?

See answer to (1)

cupstacker:
3.) how many RGB leds can you control with 1 chip and which?

See answer to (1)

As discussed, there are many ways to get there grasshopper!

For example, say you were to make an 8x8x8 RGB LED cube.
One way to multiplex is to use 64 RGB LEDs per layer.
64 RGB LEDs means 192 LEDs per layer.
If you had common anode parts, one way to get there is to use a P-channel MOSFET to source current for each layer, and 192/8 = 24 8-bit shift registers to sink current from the individual cathodes. PWM the output enable to have brightness control of the layer. Use SPI.transfer()s to load the 24 bytes per layer in ~30uS, have each layer on for 1mS for 125 Hz refresh rate.
(1/ (.001S/layer * 8layer) = 125Hz)

Alternately, use cd74HC164 to drive the anodes in each layer, and N-channel MOSFET to sink the current from each layer. Have to PWM the N-channel in this case as that shift register does not have an output enable.

Or, use 11 parts like WS2803 to sink current for 18 cathodes, and have individual brightness control. Or 12 parts like TLC5490 - that one has more levels of brightness control; both parts need a lot more data sent because more than just on/off is being sent for each LED.

Making a flat display? Look at MAX7219, $1.25 each at taydaelectronics, can control 8 columns of 8 common cathode LEDs. If use 2 common cathode RGB LEDs/column, (so rows are not used), each chip can drive 16 RGB LEDs.
With some multiplexing, can have 3 chips drive an 8x8 RGB LED Matrix.

Many solutions for each situation.

If you've got a 1000V power supply you can light up tens of thousand of LEDs with a single chip.

Yep, strings of 300 LEDs with Vf = 3.3V if you had 1000V rated transistors.
Or relays I guess. Only switching 20mA.
Parts are a little pricey

CrossRoads:
Parts are a little pricey
http://www.digikey.com/product-detail/en/IXFB44N100P/IXFB44N100P-ND/1994992

And you need a driver for the gate of that chip, to use it with an Arduino.

Yes, simple transistor to let Gate go from 0 to 10V.
No Logic Level gates on the high voltage parts.

looking to accomplish something like this

that right there is 100 rgb leds. i want to control each individual led, be able to fade color to another color.. i don't know if i want 100 rgb's or 200/250 rgb leds.

so i am seeking the proper chip and how many also brings me to resistors of how many and which

thank you

Check out WS2801, daisy chain as many as you want, one per square.

WS2801.pdf (423 KB)

:astonished: that's a lot of chips, i don't think that's the angle i want to go

thank you though

Well, then there’s WS2812B, combines chip & LED in one device.
Make a little board with in & out signals, mount them in their own pockets in your table.

Chips themselves don’t seem very pricey
http://www.ebay.com/itm/like/261322802114?lpid=82

Pre-mounted - how spread out did you want them? 8)
http://www.ebay.com/itm/4M-60LED-M-WS2812-5050-SMD-WS2811-Built-in-Individually-Addressable-RGB-Strip-/111138125443?_trksid=p2054897.l4276

WS2812B_preliminary.pdf (347 KB)

WS2812B_breakout.png

WS2812B_sch.png

pretty cool, but i couldn't find them on ebay - looking for a green board with an led? or does it look like a square led?

thank you

I just posted links for them.

so i just pop one of those white squares in each hole i want and then it's just a matter of wiring them up? what about resistors?

http://www.ebay.com/itm/like/261322802114?lpid=82

otherwise the premounted i couldn't say how far apart i want them..

thank you

I posted the datasheet in reply #12 - no resistor needed. Just a 0.1uF cap per device across power & Gnd.

keeping in mind that the box is made of wood or whatever i decide to use, they don't make circuitboards that big, so i would like to see how to daisy chain / wire these up.. any schematics?

thank you

Look at the datasheet.
Look at the board schematic I posted.

You can have boards any size you want - smaller is less expensive.
Did you want just 10, 20, 30, 40?
http://imall.iteadstudio.com/open-pcb/pcb-prototyping/im120418001.html?options=cart
Did you want 50 or more?
http://imall.iteadstudio.com/open-pcb/small-batches-pcb/im120418013.html?options=cart

Did you want to put several on a 50mmx50mm board and cut the boards apart yourself?
Or put one at each corner of a square board and mount it so the 4 LEDs each face up into their own pocket?

This guy has already done what you're looking to do, and much more. Take a look at his website and you can follow his instructions, or at least gain a grounding of a way that can work.