Creating LED display that can vary brightness | LabJack

Creating LED display that can vary brightness

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jaisler
Creating LED display that can vary brightness

Hello. For my job we need to create a LED display with a red, blue, and infrared LEDs in order to test the image quality for CCD cameras we are working with. I was given a LabJack U3-LV and was wondering how I could go about programming and making this using the LabJack or any advice. Once we connect the LEDs to the LabJack (with resistors for each LED) we will be able to program them to vary their brightnesses, correct? Is there a specific function/set of functions within LabJack necessary to achieve this? Is the assumption that we can just connect the LEDs to ports in our LabJack correct? Additionally, is there any advice anyone has on how to achieve this more easily or effectively, or tips on how to do it?

Thanks

LabJack Support
So 3 LEDs, correct?
So 3 LEDs, correct? What is the max current you need to source to each LED?
jaisler
Correct, 3 LEDs, and it looks

Correct, 3 LEDs, and it looks like the max current needed to source each is 700mA

LabJack Support
The normal solution to vary

The normal solution to vary the brightness of a high power LED would be to use PWM to control a switch which turns power to the LED on/off at a very fast rate, thus presenting an apparent average brightness that varies.

1. You need a power supply that provides at least 2100 mA at the voltage that winds up working with your system. Perhaps ~3 volts.

2. You need a resistor in series with each LED to set the current to the max value you want. These resistors will be dissipating some power so you want power resistors.

3. Add a switch in series so you can turn power on/off to the LED at a fairly fast rate. A normal switch we look at is the Jameco 175222 (Kyoto KF0604D), but max frequency is 70 Hz which is probably too slow, so might have to find a faster switch.

4. You will use PWM outputs from the U3 to control the switches. For example, say you turn the switch on for 250us and off for 750us and repeat. That means the average power delivered to the LED will be 25% of the max. The U3 has 2 PWM outputs, so you need to use 2 U3s or move up to the U6 or T7.