USB-UIRT Forum

Hello,

I bought 2 IR Led to connect to USB-UIRT; I read on this forum the internal resistor limiting the current is quite hight, 82 Ohm so the USB-UIRT provide a low current to external LED;

The specification for the IR LED I Use (CQY 89) is 100 mA.

What is the maximum current the USB-UIRT can drive ?
The max instantaneous current ?
Can I plan to change the internal limit resistor by a lower value ? What is the lowest value ?
Can I change the resistor by a resistor in parallel with a low capacitor (like 0.1 uF // with the original 82 Ohm) to allow a high pulse instantaneous current and limit the mean current to a low value ?

Thanks.

I believe the capacitor is a bad idea, since it will badly mis-shape the IR pulse-train.

You can probably drop the internal resistors safely down to 10 ohms -- that is the value to the two (in series) built-in high-power emitters. This would give you about 250mA out to two IRLED's placed in series. This is more than your spec, but you're never greater than 50% duty cycle. More current than this and you're going to see USB power problems. I would also strongly suggest that if you crank up the 1/8" jack output power, you either disable electrically or with the Zone feature the built-in emitters.

-Jon

thank you for your answer