Newbie Needing Assistance - Pulsing LED's

I was asked to help a student create a stand of 30 LED lights that pulsed on and off for five minutes at a time.

I plan to buy an Arduino UNO, a push button switch and 30 LED lights from eBay; as well as some wire to connect all the lights in a strand (just in case). I found code that should work; but what I have a question with, is, will the processor by itself have enough power to power all 30 LED’s plus any other parts I may need.

I thought I may need a Relay, but then, I believe, that I would not be able to pulse the LED’s through the relay.

So, any help I could get would be great. This is a non-paying job, and if I understand right will need to be completed in just over a week from today.

Thanks in advance.
Brian

will the processor by itself have enough power to power all 30 LED's

No. The simplest way is to use a strip of addressable RGB LEDs and provide them with a seprate supply, Sparkfun or Adafruit sell them with code and wiring examples.

No matter what, you will need an external power supply.

If you are individually setting the color and brightness of each LED individually, use individually addressable LEDs as suggested above (WS2811, WS2812, or WS2812B) - these are available as peel-and-stick strips, strings like christmas lights, on individual breakout boards, or in arrays ("Neopixels" is one brand) . These are cheap and work well, and you can put as many on the string as your power supply can handle (5v@~60ma per LED), or more if you're careful not to light them all up at once.

If you're controlling the LEDs all at once, or in a few groups, you can use (groups of) leds in parallel or normal RGB LED strip (which is a bunch of RGB LEDs hooked up in parallel). In this case, you'd need to use MOSFETs* (a relay would only allow you to turn it on or off, not vary the brightness with PWM) to switch the power to the LEDs on and off. I think this is probably more educational - but individually addressable LEDs would be easier and could potentially look much cooler.

*Preferably N-channel enhancement type MOSFETs on the negative side of the LEDs.

Will the processor by itself have enough power to power all 30 LED's plus any other parts I may need.

No! One Arduino output can power about 1 LED. The spec is 40mA maximum from any one output pin, and I believe 200mA total. (A standard-everyday LED requires about 20mA.)

I thought I may need a Relay, but then, I believe, that I would not be able to pulse the LED's through the relay.

A relay should work fine.

Get a relay with a coil rated at 5V, and a coil current of 40mA or less. (There are some relays especially designed to work woth the Arduino.) The contact will need to handle the LED power (voltage & current) but just about any relay should be able to turn on/off 30 regular LEDs.

If you get a solid state relay look for one that works with a 5V control voltage. They usually work with a range of voltages and 5V solid state relays are far more common than 5V mechanical relays. Make sure the solid-state relay is rated to control DC.

Do you know how the LEDs will be wired? LEDs require a "constant current" power supply, and with standard (low-power) LEDs, that means just a resistor in series with each LED.

I was asked to help a student create a stand of 30 LED lights that pulsed on and off for five minutes at a time.

I assume that means on for 5 minutes and off for 5 minutes? If the timing is not too critical, you can use an [u]NE555[/u]. A 555 timer is less than ond dollar and it's "programmed" by selecting resistor & capacitor values so you don't need any software programming. But, the "analog" components are not as accurate as a crystal (or resonator) in a microcontroller. You could also build a crystal -controlled hardware-timer, but the Arduino and a littel software would be easier if you don't already know how to do it.

DrAzzy: No matter what, you will need an external power supply.

DVDdoug:

Will the processor by itself have enough power to power all 30 LED's plus any other parts I may need.

No!

Both wrong. LEDs can be multiplexed. 6 rows, 6 columns gives up to 36 LEDs. Drive each LED at 6mA (36mA sink current on the column pins). Average brightness (with a 1/6th duty cycle) will approximate the brightness of a 1mA LED, but most modern high-flux LEDs are visible indoors with that amount of current.

The real question is, how bright does the OP want his LEDs? Depending on that answer, the Arduino may or may not be able to drive them directly and external hardware may or may not be necessary.

Hi, before we go any further we need to clarify something. Do you want to flash all the LEDs together? Or do you want to flash separate sets of the LEDs independent of each other.

As I read the OP request, one lump of LEDs all flashing together, ie one output to control all the LEDs.

Tom....... :)

but most modern high-flux LEDs are visible indoors with that amount of current.

There a is a difference in being visible and being what a normal person would expect an LED to look like. Also while some modern devices would do that I would not say that most LEDs sold are of such modern design.