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I have a 5V LED strip that used to be behind a TV powered by its USB port - but it got mangled by the dog - and I can definitely use the scraps for a raspberry pi project. I have done my research prior to posting but most of the topics online are referring to driving a 12V LED strip.

I have Raspbian Jessie With Pixel & Pi 3 Model B

Here is the LED strip I have: https://amzn.com/B01HTEXN76

And in case of link rot - here is a picture:

enter image description here

I only want to use 10 segments and each be controllable via PWM. From the research I've done I've read that LEDs can use up to 60mA each, but I don't know if people just take that into consideration for 12V strips only or not.

I was wondering if someone could help me with the wiring diagram.

The other topics stated buying a DC power jack etc but I don't need one cause I have a 5V LED Strip. And since it's 5V LED Strip and my power supply for my Raspberry Pi is 5V & 4.8A (2x 2.4A USB ports) see here on Amazon: https://amzn.com/B00QTE09SY

I thought I could just used the chewed up USB cord, cut the chewed up part off (the part of the led strip that had a controller you can see it the Amazon links picture) and wire the ground to the Raspberry Pi ground, and then proceed with wiring the positive wire to the 5V line of the LED strip.

Im guessing I would have to set it up somewhat like this: http://popoklopsi.github.io/RaspberryPi-LedStrip/#!/

However, I wont need the power jack because I have a chewed up USB cord that I can just cut and rewire with and plug that USB end into my power supply.

So my question is will I need MOSFETs if Im only driving up to 10 LED's with the same voltage as raspberry pi? Or can i just use a diode to block back current? If so, which ones would you recommend?

Thanks for you understanding and patience with my Pi noobiness

soulshined
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    Correct @SteveRobillard and thanks for the response. My concern is about current going back to the Pi and ultimately rending the whole device useless. So your saying all I need to do is attach the + to 5V and RGB to GPIO pins. What about grounding it? Do I just take the - from the USB and put it in the ground GPIO? I just don't want mess anything up because everyone online is using transistors or diodes but again, all those examples are based off 12V strips – soulshined Oct 19 '16 at 03:42

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You will not be able to power it from the Pi 5V pins on the expansion header. No matter what the ratings of your power supply, the current in limited by a polyfuse to 2.5A - less that needed to run the Pi and any other peripherals. See Raspberry Pi Power Limitations for detail.

You may be able to run it from a separate 2.4A. NOTE if the PSU is designed to charge smartphones, it will probably supply 2.4A, but may drop the voltage to 3.6V. The only way to know is to test it.

I don't know the detail of the LED strip. If it has controllers driven by logic levels then you should be able to run from GPIO (watch the voltage, it should not exceed 3.3V or you could damage the Pi). If the strip needs more current on the RGB inputs you will need MOSFETS, and you could use these in any event.

This is easily tested (without even connecting to the Pi) with a multimeter.

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Milliways
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  • Hey! Thanks for the reply! Yeah I updated my question with relevant links to the power supply and deleted the paragraph about me plugging it in the 5V pin, i didn't want people to think that was my intention. I know not to do that based off all the how-to's online. My power supply has 2 usb ports each with 2.4A. So my final decision was to plug it into the power supply with the chewed up (refurbished) USB cord, take the USB + to the 5V + on the LED strip and then connect RGB to the GPIO with a common ground to the Raspberry Pi but wanted to run it by anyone and everyone that knows their stuff – soulshined Oct 19 '16 at 03:56
  • But essentially, your saying it doesn't hurt to use MOSFET regardless of the need for them – soulshined Oct 19 '16 at 03:57
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    @soulshined I regularly use MOSFET, even for relatively low currents. This way you are protected from excessive voltage on external devices. – Milliways Oct 19 '16 at 04:03
  • Okay I will test with a multimeter and get back to you before buying anything. Thanks @Milliways – soulshined Oct 19 '16 at 04:12
  • Milliways I plugged it into the wall socket, cut down the strip to 10 LEDs and its showing a reading of 5V - from a 5V 2.4A power supply. Does it matter which MOSFETs I get? – soulshined Oct 19 '16 at 04:49
  • Put the meter on a current range. Connect from a RGB to ground (the LED should light) to determine current. I use cheap BS170 (cost 20c) or BS270 these can switch up to 500mA. You may need higher power devices. You need MOSFET with a low Gate Threshold Voltage (3V or less) to switch reliably from the Pi. – Milliways Oct 19 '16 at 05:30
  • Sorry for the late reply. Getting ready for bed. I checked out the B line and it came out at 97mA (for 10 LEDs) G is similar and R is similar – soulshined Oct 19 '16 at 06:51
  • [this one](https://amzn.com/B00LQOZ270) should do just fine right? it states in the description Vgs is 3V which is under your recommendation of keeping it under 3.3V – soulshined Oct 19 '16 at 19:25