I have two questions… the first isn’t necessarily a FastLED issue but this forum has such great support I hope y’all don’t mind if I pose it here…
I’m about to hang a sign that’s using about 70 2812s. I’ve designed the fixture and everything - I’ve added a 1kuf 25v cap in line with the +/- voltage to the strip, and will be powering the unit from an Arduino Uno. I’ve measured the usage of my fixture and it seems to be between 4-5 watts. I’ve got a 2amp 5v power supply that should be more than enough.
I was going to use some 22/4 unshielded wire ( think solid core phone cabling ) to drive the sign. I was thinking of putting the Arduino inside the sign itself, but now I’m thinking I’d put the Arduino about 5-10 feet away and push the power and data signals over 3 wires of the 22gauge 4-strand. Does anyone see any problems with this? I was also going to run the 3 wires straight off the Arduino instead of running power directly to the strip - does this seem ok? Is there any real advantage to bypassing the Arduino 5v output and going directly to the strip when I’m pulling less than 1a?
Also, if that 22/4 wire is good to push voltage + data to the strip, how long can such a control line be before it might have issues?
If you put the Arduino away from the strip, you’ll have to add a resistor to the data line. Let’s say about 370 ohms.
The 5V PS wire can plug directly into the 5V pin of the Arduino as well as the strip. Just don’t plug anything into the Vin line.
Those 70 LED’s are capable of drawing up to 4.2A (70 LED’s * .06mA max each), so if you want to drive them directly off the Arduino, you’ll really want to use the power managed functions of FastLED, or you will have problems if you don’t know what you’re doing.
I tested this strip and program and they’re pulling a lot less. I’ve also test-run the setup now for a few days and the 2a power supply runs cool with no trouble.
What are the “power managed functions” you’re talking about?
Any idea how long the control line can be before there are problems? Why does there need to be a resistor on the data line?
I tested the setup with about 18 feet of 22/4 and it seemed to work. I put a 330 ohm resistor on the data line - does it matter of that resistor is at the near or far end of the cabling? I put it on the arduino side and it seems to not affect performance as far as I can see.
Resistor should be near lthe LEDs, it’s there to attenuate noise on the data line. Off the top of my head 22ga is good for what you doing ~5amp, just watch the distance, 53ohm ohm/Km @22ga. I wouldn’t power the strip off the arduino imo.
After trying different setups, it does look like it’s best to power outside the Arduino. so I’ll run the power supply to the strips and the arduino via the pins.
If the resister is on the arduino side does that defeat the purpose?
Here’s another quick question… on this string of 70 LEDs, i have them broken into three segments. The third (farthest most) segment randomly blinks on and off. The first and second segment simply change colors but stay on. I notice that when the third segment blinks, the first two segments dim ever so slightly about the same time the third segment blinks. Is this normal? Is this something that would be allieviated if power was supplied to both ends and/or the middle of the strip?
My project is pretty much already sealed so I won’t be testing it. Was just wondering if this is a common behavior of only applying power to one end? I’ll have to keep that in mind for future stuff.
Measure twice, cut once. Test a BUNCH of times, seal once.
Have you completely sealed off the sign? What happens if an LED dies or a connection fails? If you have any access at all, it’s super simple to run some extra power leads.