Power and Signal cable length in an LED project

[Davidelvig]

I have a project with:
- an amplified microphone (from @Neutronned) on a bedside table next to a clock radio, along with some buttons to change LED pattern effects
- LED's surrounding the bed's canopy
- power outlet on the wall near the bedside table

The guidance for LED projects is to "keep the cables short".
Of course, the mic leads cannot be overly long either (though they will be amplified).

The distances involved are as follows:
- from the clock radio to the top of the nearest bedpost: 118" (radio to the post then up to the top)
- from that top of bedpost to the start of the LED strip: 24" (from top of post to start of LED)
- from that top of bedpost to the end of the LED strip: 79" (I need to power both ends.)

Ideally, the Teensy would be on the bedside table with the microphone.


Any guidance?
- teensy placement
- power placement
- power and signal line gauge

 

[PaulStoffregen]

Generally you would run the power first to the LEDs, then from the LEDs to the Teensy. The LEDs use a lot of current relative to everything else, so you want that connection to be direct, so the LED current doesn't flow through any other wires. What wire gauge to use between the power supply and LEDs depends on the maximum current, which can be estimated from the number of LEDs (a detail I don't see).

The general guideline is 50 mA per LED, and you want to keep the voltage drop along the wire under 0.25V and ideally under 0.1V if you can. By Ohm's law, you divide the max voltage drop by the max current to get maximum resistance you can tolerate. Once you know the max resistance, you can look for wire that meets that need.

Use google to find lots of site that tell you the wire resistance per foot or meter. Since you know how long your wire will be, and how much resistance you can allow it to have, it's pretty simple math to check which wire sizes give you that resistance or less.