Resistors for LDD driver

Other Hardware General Electronics
1

Over a year ago I built an led light using LDD drivers (http://www.meanwell.com/search/LDD-H/LDD-H-spec.pdf) and I recall having issues wiring them up the first time. I found a diagram online that worked well for me but unfortunately the full size image appears to be gone, a smaller copy of the image can be seen here (Arduino & Mean Well LDD Drivers | REEF2REEF Saltwater and Reef Aquarium Forum). The part that I was not doing correctly is placing a resistor in between the pwm signal and the ground. My question is why does this need to be done and what size resistor should be used? Upon inspection of my current light that works, I used 1k ohm resistors but have seen online people saying to use 10k ohm (http://www.ultimatereef.net/forums/showthread.php?726703-How-To-Wire-up-LDD-Mean-Well-Drivers-with-Arduino-Dimmer-Control). Would this cause a problem if i use less ohm resistors?

I found a thread where someone thinks you can simply connect the vin- on the driver to the ground on the arduino to get it to work (UkReefs.com is for sale | HugeDomains). If this works the same it is simpler as it does not need the resistor. Can anyone give me some guidance on how to properly wire this up.

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The resistor will hold the voltage on the PWM line low (and the LED off). I can't find it in the documentation for the driver but I suspect that the driver has an internal pullup that will keep the voltage high when the PWM input is left disconnected.

1K to 10K is fine. The 10K would be preferred because you'll drain less power from your Arduino output through it. V/R = I, so 5V / 1K = 5ma. It's only 5ma, big deal, but the 10K resistor would lower that to .5ma. Not something to lose sleep over but the 10K would be preferred.

3

I have never used these Meanwell drivers, but I have worked with other LED drivers.
The PWM input of those was a current source to an internal 5volt line.

A resistor to ground is not needed when Arduino drives the PWM input.
But when you turn the Arduino off, or during bootup, Arduino pins are tristated (open circuit).
Then the led drivers are fully on.

If you don't want this to happen, you have to add that resistor to ground.
In my case, 10k was always enough to turn the LED driver full off.
But the Meanwell datasheet states a maximum PWM current to ground of 1mA, and an "off" voltage of >0.8volt.
That means that ~820ohm could be needed to fully turn them off.

I guess you have to try 10k, 4k7 and 1k from PWM input to ground on the Meanwell driver.
No Arduino connected.
And see when the LEDs are full off.
Leo..