Feasibility of project/ do I need resistors?

Hi, I’m very new to this stuff so please forgive my ignorance. I have a project in mind, but I’m not sure about the details/feasibility, so I thought it would be better to post here before I end up buying parts that aren’t compatible.

I’m planning to make the circuit I’ve attached, with 13 SK6812 LED strips (60led/meter) that are cut to 77cm each (10m, 600leds in total), 13 AM312 PIR sensors and an Elegoo Mega 2560 R3 with a 5V 60A 300W switching power supply.

I’ve done a lot of reading and I’ve gathered that the strips will need a total of 180W (18W/m * 10m) and will have a current draw of 36A (180W/5V).

I know how to calculate resistance but I don’t know how to work out which resistor I need or if I even need one at all in this circuit. Any help would be appreciated.

Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
http://forum.arduino.cc/index.php/topic,148850.0.html.

Adafruit suggest for the Neopixel.

  • Place a 300 to 500 Ohm resistor between the Arduino data output pin and the input to the first NeoPixel. The resistor should be at the end of the wire closest to the NeoPixel(s), not the microcontroller. Some products already incorporate this resistor…if you’re not sure, add one…there’s no harm in doubling up!

Tom... :slight_smile:

These strip incorporate a control chip and looking at the data sheet should be powered just from 5v, so no resistor - but check

( last page has a wiring diagram )

Think I would power separate sections ( try in two lots of 5 strips with power going to the centre one and looping outwards to the two on either side ?) radially rather than looping from one to another or the supply cable voltage drop will make the distant ones dimmer .

Hi,
Can I suggest you down size to get your project going,
Just try and control ONE strip, forget about the PIR for the moment.

This will need to be done in stages.

Also your wiring, when you get to that part, will need to be heavy enough and layed out to minimise losses and provide good regulation to the strips.

Tom... :slight_smile:

5V supply should go to 5V on the Mega, not to Vin; spec for Vin is 7V minimum.

Be careful when connecting both USB and 5V (on 5V pin) to the Mega at the same time; I'm not sure what will happen.

sterretje:
Be careful when connecting both USB and 5V (on 5V pin) to the Mega at the same time; I'm not sure what will happen.

Small risk (same as with UNO, but not Nano) of "back-feeding" excess 5 v into the USB port of the PC/ laptop and at least temporarily upsetting it. Do not use "Vin" of the Mega for any purpose.

To be clear, there is no suggestion that resistors have any purpose whatsoever in the power supply of the addressable SK6812 strips however you should incorporate a series resistor - about 330 Ohm - in series with the data input of each strip that is any significant distance from the source of data or is connected to a different 5 V power source.

500 µF or 1 mF capacitors are advised across the 5 V and ground at the start of each strip and you should at least be connecting that 5 V and ground to each end of each strip and ensuring that where the data output of one strip connects to the data in of the next, the two respective grounds are connected at the same points by wire that travels as a pair with the data wire.

Thanks for the replies guys, I've ordered the parts and will try and get one strip working first without the PIR sensor as suggested.

I've attached an updated diagram of my plan.

I'm not sure I understand the bit about connecting the 5V and ground to each end. Is this to avoid discolouration? The strips will only be 77cm each.

Paul__B:
500 µF or 1 mF capacitors are advised across the 5 V and ground at the start of each strip and you should at least be connecting that 5 V and ground to each end of each strip and ensuring that where the data output of one strip connects to the data in of the next, the two respective grounds are connected at the same points by wire that travels as a pair with the data wire.

Yes, but you still have the power going only to the left hand side of the strips, so discolouration particularly at full white is a potential concern, and you have the data feeds at the right hand ends of the strips having no ground reference which for a radio-frequency (or really any frequency) data communication is a really bad idea.

77 cm of LEDs at 60 per metre, is easily 2.5 Amps at full white, and the foils on these strips will drop significant voltage, affecting the blue LED components the most as they have a higher voltage drop.