Beginner question, regarding how many Volts to use

Hello! I'm new to all this electronics stuff so I'm sorry if I don't fully understand my own problem here. i'm just hesitant to even start the project because i don't want to blow something up.

my project is simple, I'm hooking up a P.I.R. (passive infrared sensor) to an LED strip, so when i pass the sensor the lights will turn on for a little while.

I have connected the P.I.R. to a single LED with resistors on a breadboard, and successfully powered it with my 9V battery. only as a test.

The LED strip user manual (it came with remote and usb,, but i only want the strips) only says "input: DC 5V. Power Consumption: Max 5W".

The P.I.R. info on the internet says "Input voltage is +5V for typical applications. Can range from 4.5V- 12V"

do i need to add the volts or something? What information do i need to to know what battery to use, or what resistors? absolutely clueless.

thanks in advance!!

by BeefJeff
April 04, 2021

Don't overcomplicate your project. The PIR says input 4.5 to 12v and you are using 9v so that's ok. The LED strip is a different matter, however. The spec is 5v and I would think 5v +/- 10% or 4.5 to 5.5 would be ok; it usually is. The 5W means 5 watts so the LED strip will require 5W / 5v or 1 amp. Your 9v battery is way too high voltage and would probably quickly damage the LED's then die from overcurrent if it's the usual size; about 2"x1"x0.5". I would suggest you buy a plug in supply rated 5v dc and either 5W or more or 1 amp or more and use it to power LED's and PIR. They come both ways and are often called a "wall-wart" . You may have to cut off the dc plug to connect it to the LED's and PIR. Be very careful to make sure you connect the + power supply wire to the + input of the LED's and PIR and - to -. The 2 wires should be colour coded for polarity but there are several colour standards. Red and black or red and white are red +. Black and white are black +

by Foxx
April 04, 2021

Thank you for your reply, this has helped so much,, its nice to see that I=P/V in action too.

I've stripped the wire that's attached to the LED strip, and i find: green, black, red and white. so i imagine the red is the +, and black is the -. Thanks again! :)

by BeefJeff
April 04, 2021

There may be more to this LED strip than is obvious. What are the "remote" and "usb" you mention? Is this a strip of neopixel LED's? I ask this because a plain old LED would need only 2 wires and you say there are 4 so this may imply some sort of smarts controlled by the remote. Neopixels are programmable for colour and brightness and require some electronics for control.

by Foxx
April 04, 2021

Ah right, yeah. The strips are part of a TV Mood light set, so I think you're right, they may be neopixels. I got the mood lights on discount because the remote control is faulty (maybe fixing that could be another project at some point).

I think I'll just order some basic LED strips so I don't overcomplicate it.

by BeefJeff
April 05, 2021

It just occurred to me there are 3 colour LED's available which use 4 wires, one for each colour plus one common so perhaps this is what you have. When you get the LED strips be sure to get data sheets for them. Regarding neopixels, I have used them for microscope illumination for mineralogical and gemological work and they work very well for this as you can get every colour there is by mixing. But they require a controller such as Arduino UNO, Mega, Nano, etc. so they are either a learning opportunity more than you want take on depending on how you look at it.

by Foxx
April 05, 2021

That is correct with the 3 colours. I was a little confused because on the actual strip, there are connections for R, G, B, 5V. I'm just not sure which to connect to ground. If I knew that I think I could make it work.

I have an UNO, but I wanted to practice more standalone projects for better understanding.

I'll stick with the basic LED strips for now, maybe I'll feel confident to work with the neopixels in the future. It sounds like they can be a useful component!

Thank you for all your help.

by BeefJeff
April 06, 2021

That's starting to make some sense. The 5v should be connected to a 5v source and each of the other 3 wires would be connected to ground to light up its colour or disconnected to turn off its colour. There should also be a resistor, a few hundred ohms in series with each of the 3 connections; it may be already in or you may have to provide it.

by Foxx
April 06, 2021

That's it!! I've a much better understanding of this project now. I know it's only a simple circuit, but you've no idea how helpful you've been, thank you for taking the time to help me, Foxx! Means a lot.

by BeefJeff
April 06, 2021
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