Tseting a long chain of individually addressable LED's (but only using some) - Page 1
Forum section: electronics / beginners

author: Youkai
author_rank: Regular Contributor
timestamp: June 06, 2022, 03:02:12 am
content: What happens if you try to run a chain of LED's longer than you have the power output for?Use case:I ordered a 1m length of 144/m RGB Dotstars. I don't know how many I'm going to want in a section for the correct brightness so my plan was to hook the whole string up to an Uno and run some tests powering on between 2 and 10 to see how many I need in my setting. Then I am going to trim the string for actual use. I'd guess that the Uno can't power 144 of the LED all at once. Do the ones I'm not using factor in to the power consumption or cause problems in some other way?

author: james_s
author_rank: Super Contributor
timestamp: June 06, 2022, 03:28:50 am
content: The power draw will be proportional to the number of LEDs you have lit and the brightness. There will be some quiescent draw of unlit LEDs but it is not much. I know from experience that a string of 100 addressable LEDs works just fine connected directly to an Arduino, I don't remember how many I tried powering at once.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: June 06, 2022, 11:33:53 am
content: Were the LEDS actually powered through an Arduino IO Pin or was it just the data line. I have many strings of these lights under my kitchen cabinets that required several 5 amp power supplies. I have a single data line commanding them all, but actual power is from multiple power supplies.

author: james_s
author_rank: Super Contributor
timestamp: June 06, 2022, 05:51:33 pm
content: Mine were powered from the +5V rail on the arduino. The key is to not light up all the LEDs at once at high brightness.

author: tooki
author_rank: Super Contributor
timestamp: June 06, 2022, 06:06:11 pm
content: Quote from: Youkai on June 06, 2022, 03:02:12 amThis scenario (more LEDs than available power) is so common that the better addressable LED libraries let you define the maximum current in software, and if you try to exceed it, it’ll limit overall string brightness.Each LED uses a maximum of about 60mA (20mA per color). That’s 8.6A for the whole string — far, FAR, FAAAAR in excess of what an Arduino can supply.You shouldn’t draw more than 500mA from the Arduino’s 5V pin. So that’s about 8 LEDs at full brightness. At lower brightness, the maximum number of LEDs scales proportionally.You’d be much better off powering the LEDs from a bench power supply.

author: james_s
author_rank: Super Contributor
timestamp: June 06, 2022, 07:27:05 pm
content: For testing though it doesn't really matter. Doing what the OP proposes and lighting up only a portion of the LEDs at a time is a perfectly valid way of testing and will work without issues.

author: Youkai
author_rank: Regular Contributor
timestamp: June 06, 2022, 07:47:04 pm
content: alright. thanks guys. Yeah this test is just a proto thing. For the final project I'll have a number of these sections connected together in a chain and I'll power them from a different source than the micro-controller. But for my quick test I was just going to use the Uno 5v pin.