connecting super bright LED's to Arduino

Hi there,

I am currently doing a project with some computer fans controlled by an arduino, inflating and deflating some standard plastic bags, which cover them. As I am interested into human interaction I need to animate the modules. I was thinking about placing a number of LED's (2 per module) inside of the plastic bag, attached to the computer fans, which gives the bags some color. I have started doing some testing with super bright LED's. So far I only used a resistor to get the LED's to work. I am running everything from a 12V battery, and everytime I connect the LED's to the battery (with the suitable resistor) they (LED's) just blow up. I guess it is related to the uncontrolled voltage / current of the batterie which causes the problem? I had a look an the forum and there seems to be two methods to get it to work, both in connection with high power led's. The first one reducing the voltage (http://www.instructables.com/id/Super-simple-high-power-LED-driver/), the second one with a setup I don't completely understand (http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/step8/a-little-micro-makes-all-the-difference/). I only need to turn the LED's on or off, nothing spectacular.

Which method is more suitable for my setup?

I was also thinking about using some 1W high power LED's, but I am not sure if they are not getting too hot, burning the plastic bag as they are going to be located inside. I could cool them down with the computer fans, but maybe someone has already had some experience with these LED's?

Thanks for your support!

and everytime I connect the LED's to the battery (with the suitable resistor) they (LED's) just blow up.

That shows you the resistor is not suitable and you are sending too much current down them.

For high power LEDs you need a constant current driver.

Instructables are, in general, rubbish do not read them, look elsewhere.

Most LEDs can only handle 5V. You can out 3 in series with your 12V source and a current limit resistor to keep the string under 20mA.

Most LEDs can only handle 5V.

No they can only handle their forward voltage, the resistor makes them able to handle any voltage because it drops the rest. There is nothing wrong with powering an LED from 12 or 24 volts.

If the reverse voltage is too high, the LEDs won't look like they are turned fully off. I used superbrightleds in my scoring machine, I needed 3 LEDs across 12V to turn fully off. 1 and 2 would somewhat on even when the drive transistors were off.

I think that is down to leakage on the transistor rather than anything to do with the LED.

The first one reducing the voltage (http://www.instructables.com/id/Super-simple-high-power-LED-driver/), the second one with a setup I don't completely understand (http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/step8/a-little-micro-makes-all-the-difference/). I only need to turn the LED's on or off, nothing spectacular.

Which method is more suitable for my setup?

In general Mike's comment about 'Instructables' is correct, but in this case they seem OK. Neither of these is 'reducing the voltage' as they are both constant current supplies and both techniques are suitable for your setup.

The sooner you stop thinking about applying voltage to LEDs the better off you will be. LEDs are rated in terms of their current, not voltage. The 'forward voltage' mentioned in the specifications is the voltage that you can expect to measure across the device after you somehow get the specified current flowing through it. When you design a power supply for an LED you must make sure that your supply can deliver [u]more[/u] than the LEDs forward voltage and then you use other components to limit the current to the required value. The 'reverse voltage' mentioned by Lefty is a value that is not normally of concern in DC circuits if you have your LED connected properly. If the reverse voltage across the LED is too high the LED will definitely be off, permanently.

Don