what is the brighest LED you can use ?

Hi

What is the brightest LED that can be used with arduino and 9v battery?

thanks

Do not run power LEDs from square 9V battries it will not last very long. You can get LEDs that will flatten them in seconds. You can not power thes LEDs direct from an arduino you need a constant current supply.

Grumpy_Mike: Do not run power LEDs from square 9V battries it will not last very long. You can get LEDs that will flatten them in seconds. You can not power thes LEDs direct from an arduino you need a constant current supply.

The issue my device will be portable and won't be able to have external power source.

Buy a LED torch then put a FET in series with the battery and control the FET with the Arduino

rogerClark: Buy a LED torch then put a FET in series with the battery and control the FET with the Arduino

Good idea! I'm not familiar much with electronics, would be easy thing to do ?

Yes. Very easy. You can either buy a FET and a resistor and wire it up yourself, or various places e.g. EBAY sellers have FET modules that already contain the input resistor etc on a small PCB with terminals attached.

You will get a small voltage drop though the FET so the LED's will not be quite as bright as without the FET in circuit. If you zero resistance, you'd need to use a relay, (again search eBay for Arduino Relay Module) Relays will waste a bit more current than the FET would, as the relay takes some power e.g. 30mA to be energized

rogerClark: You will get a small voltage drop though the FET so the LED's will not be quite as bright as without the FET in circuit.

would you notice the difference ? when fading up an LED, my steps at minimal brightness have noticeable changes from analogout of 1 to 2 and 2 to 3. near full brightness, I jump over 10 and do not detect any change with the eye.

rogerClark: Yes. Very easy. You can either buy a FET and a resistor and wire it up yourself, or various places e.g. EBAY sellers have FET modules that already contain the input resistor etc on a small PCB with terminals attached.

You will get a small voltage drop though the FET so the LED's will not be quite as bright as without the FET in circuit. If you zero resistance, you'd need to use a relay, (again search eBay for Arduino Relay Module) Relays will waste a bit more current than the FET would, as the relay takes some power e.g. 30mA to be energized

Thanks legend !!! I'm gonna get this one from the local store: http://www.jaycar.com.au/productView.asp?ID=XC4244

The other issue would be how I can wire the led torch? say i get these cheap torches :http://i.imgur.com/taS7dxC.jpg how to connect it to my board?

Thanks again !

Grumpy_Mike: You can not power thes LEDs direct from an arduino

Correct, you need some driver (BJT, Mosfet...)

Grumpy_Mike: you need a constant current supply.

Assuming his max voltage would be 9V he can calculate the duty cycle required to power the LED and set up a correct PWM. It could even be changed by reading an ADC and changing duty cycle. Thats how most Chinese high power torches regulate power to the LED. Check your LED datasheet for the maximum allowed pulse current and duty.

Using 9V Batteries is the same as getting a high power torch powered from AAA batteries. If you want the real stuff get yourself a 7.2V lithium Battery, composed of 18650 cells, otherwise you might as well chose a 0.5W LED, After 1 minute brightness will be the same.

CS

Assuming his max voltage would be 9V he can calculate the duty cycle required to power the LED and set up a correct PWM.

No you can’t. There is no feedback from the PWM meaning there is no limit on the peak current. Therefore there is no control over the average current. You can do that sort of thing with motors but not LEDs.

Thats how most Chinese high power torches regulate power to the LED.

And that is an example of good design?
No those torches work because of the internal resistance of the battery and the fact that they are a throw away thing that is not designed to last. In fact that sort of design is guaranteed to fail.

There are many 7 segment displays that use no resistors. They use multiplexing and each LED is fed directly from 5V with no resistor with a given duty cycle, as to be able to refresh the complete display. I saw them being extensively used in the 90's before LCD's become popular, in alarm clocks and some large displays, and they lasted years. The LED manufacturer specifies the maximum peak current and duty cycle that can be used for calculations, such as a rectifying diode sees high current peaks, many times its rated current, at the peak of the sine wave.

As with anything care must be taken, if a software error turns the pin high the LED will smoke, the duty cycles need to be calculated carefully and the LED must have adequate heat-sinking and quite possibly some temperature compensation

If you wish to further refine throw an inductor in parallel with the LED and the inductor will supply the average current in function of the PWM duty cycle, just like a motor.

This is such a good design as any other if everything is set up correctly, I am just adding one extra option

if a software error turns the pin high the LED will smoke,

. . . if you're lucky. If you're unlucky, it'll take the processor with it.

AWOL:

if a software error turns the pin high the LED will smoke,

. . . if you're lucky. If you're unlucky, it'll take the processor with it.

I meant using an external switch (mosfet, BJT), not directly powered by the arduino. An opto-coupler is also a good insurance, should the transistor itself fail.

There are many 7 segment displays that use no resistors.

No.

Sigh, Another one who doesn't understand LEDs yet thinks he knows better than any one else.

Look for "high brightness" or "ultra-bright", etc. Take a look at [u]this page[/u] in the Jameco catalog. The light output is given as mcd.

"High Power" LEDs (1W or more) are different from "high brightness" LEDs. High power LEDs are normally run from a special constant-current power supply and they cannot be powered directly from the Arduino.