1 watt leds

Hi all,

Well my other topic hasnt ended yet and i have a new one already… Sorry fellas.

I bought some leds today and the guy in the shop was kinda weird so i didnt understand one bit what he was saying. So back to the Arduino community :slight_smile:

So i was wondering how i should wire up my two 1 watt leds

I have a red one (1 watt star 625nm - 30 lm)
And i got a blue one (1 watt star 475nm - 10 lm)

i did understand that i cant wire them up to a Arduino using only a resistor. What should i use and why? Please explain me in plain english because im not an electronics guy. I understand the basics but when i heard the guy this afternoon i felt like such a sucker thats in way over his head…

Thanks guys :slight_smile:

Yes those suckers draw a whopping 350mA at 3.2V to 4V The arduino can at most drive 40mA (pushing the limits hard)

The USB cable is not gonna like more than 150mA so basicly...

You need to power the led from a transformer that outputs between 3.3V and 4V with at least 350mA or more.

So what you want to do is use a transistor and send the signal from arduino to the transistor and the transistor switches the powersupply voltage on/off to the led for you, so almost no power is used from the arduino.

The image is taken from the arduino playground (wich you should read a bit from) and the transistor used here is: http://en.wikipedia.org/wiki/2N2222

Additionally you need a few resistors 1. from the pwm pin 2. to the led from the powersupply, use a led calculator on the web this depends on if the powersupply gives more than 4V

the schematic shows many leds but just ignore the first 3 of them the schematic also shows the ARDUINO+5V, this is where you place the powersupply.


The reason you cant run it directly off of the microcontroller is that theres a limit to how much power it can have going directly through it. Theres typically a per pin limit and a chip-wide limit.

You're going to need two pieces, a transistor to switch enough power, and a current limiter. Since the LED is so big you're going to not want to use a resistor for current limitations.

I've got a 3w rgb sitting on my desk waiting for me to figure this all out.

You could use the leds at a very low power level directly from your arduino, but it wont be any fun kind of bright.

Somebody on the forums is making a shield that holds 4 of these http://ledsupply.com/buckpuck.php but at around $20 a module it would make sense to use them for more than one LED.

Actually in richmond, near the olympic speed skating oval theres some lights along the path that look like its got 54 1 or 3 watt leds in it.

Ideally you would use a constant current circuit to prevent damage to your led. For example: http://www.instructables.com/id/Power-LED_s---simplest-light-with-constant-current/step1/What-you-need/

There are also many other ways to create a constant current source. Try googling for some more examples. There have also been quite a few threads on this subject here in the forums you could read through.

You could also go for a simple logic level MOSFET and current limiting resistor setup but you risk damage to your LED from things like thermal runaway and fluctuations in your supply voltage.

You can buy constant current drivers on Ebay, both 1W and 3W. Sure Electronics does some at a decent (low) price.

well i was planning to hook up the Arduino to a powersupply but my guess is that that isnt going to cut it...

Second, i want to hook up 2 and each of them will respond to a motion sensor separately. And that isnt going to make this easier, right? And, if i understand correct from the example that ArduinoM gave, i need another supply to power the leds. That kinda sucks, it makes the project alot harder.

I keep wondering that its kinda weird that these led are 3 somthing volts and the Arduino gives 5 that it should be fine, apperently im to much of a plug and play kinda guy and thats not an advantage :-/

So what is a easy way to go from here? Just figure this out with the bright leds? (And risk it that i will ask alot of questions about it because i know squat about this type or wiring)

Or do you guys have another suggestion when it comes to a bright source of light? As an example, i bought a flashlight with 9 leds in it and it runs on 3 AAA batteries. Is that an option? Can i replace the batteries with the juice from the Arduino?

I might as well explain the project, makes thinking about it much easier.

I want 2 light sources behind a canvas (made of fabric that is not as dense as real canvas) from different angles so that the colors mix. Then there are 2 motion detectors that trigger a fade of the leds. Should be cool to see a painting made of lights (in a very basic way).

Again, thanks alot! This communitie is really a powerfull source of knowledge, lets hope that i can do my part in it :-)

I am not that familiar with high current LEDs. How important is it with constant current on those leds? I mean those things cannot cost that much that it is not feasible to change them once in a while :frowning:
A well chosen cap should smooth out ripples in dc-supply right?
my biggest leds used are 3.6V 20mA ultra blue (3500 mcd), just the right size for testing 3.3Vout pin on the arduino with pwm pin as ground :wink:


I am not that familiar with high current LEDs. How important is it with constant current on those leds?

Many would state, me included, that these 1 watt and above power LEDs should always be driven via constant current drivers. I bought one of those Sure Electronic 3 watt CC drivers and it works well, gives you a TTL contol input that the Arduino can drive either as on/off or PWM for variable brightness.


How important is it with constant current on those leds?

It doesn't have to be constant current (you can drive them with a low and/or varying current to dim them, for example), but it's very important that you keep them below their maximum specified current: hook one of them directly to, say, a 5V 1A supply, and you'll quickly change it from a LED to a FED (Flash Emitting Diode) :(

As a general rule, the higher the nominal current rating of the LED, the fussier it gets about not exceeding the maximum to avoid damage.

How important is it with constant current on those leds?

Controlling the current in a high power LED is tricky because the voltage across (and hence the current through) the LED changes with temperature. This means that it is imposable to set the current correctly and keep it constant with just a resistor. Hence if you try the brightness will vary and you could end up either running the LED a lot dimmer than it should be or risk burning it out.

I found a tutorial on Youtube about this subject.


Whats your thought on this video?


Not shure if the used led is 1 watt...

specs of the radioshack site:

  • Ideal for hobbies and electronics projects
  • High visibility, 5mm Round T-1 3/4
  • Intensity 7000mcd (typical);viewing angle 30°
  • FW current 25mA; FW supply 3.3 (typical), 3.6V (maximum)
  • RoHS compliant

Whats your thought on this video?

I think they are being ultra cautious about the maximum current for the arduino, 50mA is well under rating it.

However this is nothing to do with your problem of driving a high power LED, this is a whole new ball game.

Hows about this one:


Posted by: metalmini Posted on: Today at 18:04:07 Hows about this one:


They driving the 1W LED with only 100mA (18 ohms resistor) so it not full brightness.

Well ok, lots of replys. It seems that alot of people have some different approaches to this matter.

But i dont really have an complete awnser, an awnser that i can work with.

So what is the best way to go? As i said earlier i want to hook up 2 of these leds in combination with 2 PIR sensors.

I wanted to make schematics but Fritzing doesnt have the PIR sensor or the high powerd leds. I have posted the request over there because i van imagine that loads of people will want to use these leds.

Or do i keep it simple (stupid) by using this thing that i yanked from a flashlight, it has 9 leds and works on 3 AAA batteries:

(sorry for the blurry pics, my iphone cam isnt good and my Olympus doesnt want to focus without a macro lens...)

So the 1 watt thread is way to advanced for me.

So this is my closing the topic comment :-)

Thanks anyway for the help guys. I just dont know enough about electronics, yet ;-)

For the people that are intrested in the 1 watt led stuff. I found a site with led drives that power 1 watt leds.