lots of leds in serial


I want to pulse 8 IR leds at 38khz.
I can pulse one at this frequency using the tone() function.
Could I place 8 IR leds in series powered off one digital pin on an arduino mega 2560?
The leds have a 1.5v forward voltage and a 50ma max forward current so im guessing like 10-20ma forward current.
Or would I run out of power. Im sorry im not sure how voltage etc works. I just know it drops some over an led?

I guess if this series approach doesnt work Il have to hook them up with each led on its own digital pin?
the only problem with this solution is I think you can only use tone() on one pin at a time.

Any advice would be greatly appreaciated

8 x 1.5 = 12V.
You'll need a transistor and a higher voltage supply.

Is there any simple ways to get a higher voltage supply? Preferably not a battery.
Thanks :slight_smile:

Define "simple".

PC supply, wall-wart, . . .

You could have 2 sets of 4 LEDs, each with its own transistor and dropping resistor with the bases wired in parallel to the tone pin. Then the voltage requirement is 6V (+Vce of transistor). That would give more choices as to power supply.

You can run 6 of those LEDs on a single pin by making 2 strings of 3.

Each string would cause a voltage drop of 4.5V -- within the 5V available from your board.

Each string would also use 20mA, or half the current available on a pin.

It's probably a good idea to add a small resistor to each string to specifically limit the current to 20mA -- 22 or 28 ohms.

If you can find IR LEDs that use 1.2V, then you could power 2 strings of 4.

Cheers guys all great ideas. I like the sound of running two strings of them and then them receiving the tone in parralel off one digital output. Il have a look at it tonight
Thanks for all the great input