How should I wire my LED strings for a home theatre? - Page 1
Forum section: electronics / projects

author: radian
author_rank: Contributor
timestamp: September 22, 2019, 11:57:39 pm
content: Hey folks. I have 15 pieces of 15 ft RGBW LED strings that I want to install for ambient lighting in a new home theatre build. Studs are exposed, so I can get creative with wiring.Here's my dilemma. I want to avoid running standard AWG 14 house wire (romex) with 110V AC to each string as then I'll need junction boxes, etc. I'd much prefer to run a wire through the drywall through a small hole. This way, in case I sell the house, the next owner doesn't need to patch 15x holes in the wall from junction boxes. So I'm stuck with a low voltage solution (<50V).My first through was to use 5-conductor AWG 18 "thermostat" wiring from a centralized controller to each LED string. Thermostat wire is rated class 2, so it can be concealed behind walls. Then I could use one wire as +12V common anode, and then the other four as cathodes for each of the RGBW lines. The strings will be up to 40ft away from the controller, and will draw 2-4A, so I'm concerned about the voltage drop as well as EMI from PWM over long distances.Another idea is to send +12V and GND over two wires, then some communication signal over the others. Then a receiving controller could PWM the string locally. The problem is that the thermostat wire doesn't have twisted pair, and I'll still have the voltage drop issue and possible EMI that back-propagates onto the power/ground wires as well.The last idea is to use 2-conductor thermostat wire to send a low-voltage AC to each string, then either use WiFi/separate CAT5 for communication.What would you do in my situation?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 23, 2019, 12:11:53 am
content: You can do the PWM at a modest frequency like 1-2kHz with slow edges, by simply increasing the value of the gate resistors on the switching MOSFETs. To reduce voltage drop, you can use a cable with additional conductors to parallel for the supply voltage.

author: radian
author_rank: Contributor
timestamp: September 23, 2019, 12:22:46 am
content: Even with modest PWMing, we're still talking 15x4 = 60 PWM lines snaking through the room. The theatre will dual-purpose as a recording studio - would all the high-frequency disturb sensitive electronics such as microphones? I couldn't find any articles online that suggest that this is the preferred method, so that makes me nervous. Most suggestion I found point towards PWMing locally, but I wonder if it would be better to transfer power to the LEDs via DC or AC... hmmm.

author: ledtester
author_rank: Super Contributor
timestamp: September 23, 2019, 12:28:59 am
content: Quote from: radian on September 22, 2019, 11:57:39 pmI would do this because a CAT5 cable run can be used for a lot of other purposes and it will be usable by the next owner of the house.100baseT only uses 4 conductors, so you could carry ethernet + power for your LEDs over one cable.There is even a standard for transmitting power over ethernet (PoE) which you might consider looking into.

author: radian
author_rank: Contributor
timestamp: September 23, 2019, 12:42:16 am
content: Quote from: ledtester on September 23, 2019, 12:28:59 amWhat about this for an idea... what if I send 48V DC and GND over 3-pairs (3 for power, 3 for ground) of the CAT5 cable and skip the thermostat wire entirely? The total surface area of 3x AWG24 wires will be 25% less than AWG18, BUT if I use 48 V then I can reduce the current to 0.25-1A. According to the PoE spec, each pair should handle up to 960 mA (Type 4).

author: radian
author_rank: Contributor
timestamp: September 23, 2019, 01:33:35 am
content: Decided to perform a small test. I cut a 2-foot section of CAT6, then twisted together two sets of 3-wires. Looped the twisted sets together on one end, and connected power and ground to each set respectively on the other end. This gives me a 4-foot long conductor comprised of 3x 24-gauge wire. I've been flowing a constant current of 1 A for the last half-hour. So far I have not been able to detect a noticeable temperature increase, neither at the individual twisted-pair strands nor the bulk cable sheathing. This gives me confidence that the CAT6 should handle the job without a risk of fire.

author: sokoloff
author_rank: Super Contributor
timestamp: September 23, 2019, 11:31:48 am
content: If you can provide the room with Cat6 outlets that would be usable by a future owner, that's a good path.Because you haven't mounted things yet, I'd consider using APA102 (2-wire power plus 2-wire digital bus) LED strips, which have individual LED control. That provides an easy way to drive from a micro (meaning you could drive from an ESP32/8266 with wifi) as well.In terms of the recording interference, the obvious solution is to turn the ambient lighting off iff it becomes a problem while recording.

author: MarkF
author_rank: Super Contributor
timestamp: September 23, 2019, 04:15:10 pm
content: Maybe you can get some ideas from Jim Conner's Digital Sky project: