FreeTrack Forum

I pulled the LEDs from my old and busted TrackIR and asked natural point for the specs on the LEDs and they replied (very quickly btw, awesome support ;)) that the LEDs have forward 5V and 16mA. I want to power them with USB, but when I use the LED wizzard and I put 5V in for the powersupply (USB), forward 5V and 16mA for LED but the calcuation doesn't work, the webage just remains in the wizzard data entry page.

I don't know much about electronics, but when I drop the LED voltage rating to just below 5V in the wizzard then the resistors shown have very small ohms. Does this mean that I should just set up the circuit in parallel without any resistors?

The reason I'm a bit worried, is that the LEDs are rated for 16mA and USB (as of wikipedia) shows that it supplies 100mA by default. I don't know enough about electronics to know whether the LEDs will only pull 16mA as the need, or will the USB push 100mA onto them frying them?

Hello vikstar

asked natural point for the specs on the LEDs and they replied (very quickly btw, awesome support ;)) that the LEDs have forward 5V and 16mA

Strange values......
IR leds usually have about 1.2 to 1.8v forward voltage.

Maybe these are special devices, with a limiting resistor already builtin...
If it is the case , you can hook those leds directly to a 5v power source, without using a resistor (since the resistor is already builtin).

AFAIK, there are no true 5v leds..... Each time you see something about a 5v led, it's either an error (usual error is to use reverse voltage instead of forward voltage), or a special led (with resistor build in).

when I use the LED wizzard and I put 5V in for the powersupply (USB), forward 5V and 16mA for LED but the calcuation doesn't work, the webage just remains in the wizzard data entry page

The wizard is made to help you choose a resistor and setting , when you use "standard" leds.

For leds, a resistor is mandatory. That means this resistor must get a little voltage to drop to work correctly.

The wizard has a few security checkings on the value you enter. One of this check is to be sure this resistor will get enough voltage to acheive its work.
Since you told the wizard to use a 5v led on a 5v power supply, this can't work, so the wizard refuses the input.

when I drop the LED voltage rating to just below 5V in the wizzard then the resistors shown have very small ohms. Does this mean that I should just set up the circuit in parallel without any resistors?

Never use a standard led without a resistor.

But since your leds seem to be special devices, try it....

The reason I'm a bit worried, is that the LEDs are rated for 16mA and USB (as of wikipedia) shows that it supplies 100mA by default. I don't know enough about electronics to know whether the LEDs will only pull 16mA as the need, or will the USB push 100mA onto them frying them?

A power supply doesn't "push" current in a device....
A power supply provides a voltage , and is drained from the amout of current the device needs.

The current value given for a power supply is a max value the psu can supply without being damaged.


So the correct term is :
your usb supplies 5V voltage, at a current up to 100ma.

If your setting need 16mA, the USB will provide 16mA.


hope this helps.


cya

Sweet, thanks for the info. It doesn't look like there is a resistor built into the LEDs, but I'll give it a go. Worst case I guess is I fry some LEDs for which I had wrong specs for anyway.

Here is a close up of one of the LEDs:

Really strange.......

They indeed look like standard leds......

A way to test it :

If you have a multimeter with a diode test mode, then just hook the Led to your multimeter.

In this mode , the multimeter provides the diode with a small amount of current and read the voltage drop on the diode.

So , if your read about 1 to 2v , thats a standard led.
If you read about 5v , it's a special device.

cya