What type of Mosfet to Drive two 5V / 2A LED Strips?

Using Arduino Motors, Mechanics, Power and CNC
1

Hey you all! I have purchased two WS2801 1 Meter, 32 LED Strips and intend to power them both at the same time from an Arduino UNO.

Given one of the settings options on my product will be for all LEDs to be on (bright white light) for extended periods of time I am opting to run them from an external 5V/4A adapter. I have a couple questions I was hoping you all could help me with:

  1. If a 5V/4A adapter sounds good to you all, what would be a good Mosfet to use if I got one for each strip (and just used the Arduino to control the flow from the adapter through the Mosfet to each strip). I know I need an N-Channel, L-Series Mosfet, but what model (V, A etc)? The calculations on that are a little beyond my comfort zone. (I believe the spec sheet on the strips calls for 5V/1.8A each)

  2. For anyone with experience using the WS2801 LED strips, will they run wide open for a long time or is there a more durable / reliable strip product I should use?

  3. I've heard that I should use a Teensy instead of Arduino because of the increased speed, but I'd rather stick with an Arduino product. I am just using the UNO for testing, but is there a better Arduino I should use for production - an Arduino product that is minimal, fast and capable of running the same sketches?

Thanks so much for any advice you all may have.

2

The WS2801 is a programmable chip with three mosfets inside. One for each colour.
You con't need extra mosfets.
The IC/strip just needs a constant voltage (5volt) supply.
Maybe you can find more info about the WS2801 on the Adafruit website.
Leo..

3

Wawa:
The WS2801 is a programmable chip with three mosfets inside. One for each colour.
You con't need extra mosfets.
The IC/strip just needs a constant voltage (5volt) supply.
Maybe you can find more info about the WS2801 on the Adafruit website.
Leo..

Thanks Wawa, but what I mean is the Arduino does not have the power to run the strips by itself so I will need to have a configuration like this:

In this screenshot he is powering a 12V strip by way of an external source and using the Arduino as a control through the gate pin on the mosfet.

I would have to duplicate this times 2 (with two 5V strips) but using a 5V / 4A supply to power both strips and I'm just not sure which mosfets would be best for the job.

4

Do you have a normal LED strip that needs mosfets.

Or do you have a digital WS2801 LED strip that doesn't need external mosfets.

A digital strip needs a beefy 5volt supply and just one-wire control DATA from the Arduino.
The data controls which LED on the strip is on/off/dimmed.

A normal strip only has smd resistors between the LEDs.
A digital strip has a (14-pin) chip on the strip for each RGB LED (5volt strip) or for each 3 LEDs (12volt strip).
Leo..

5

I need to run 2 of these:

and combined they would draw around 4 amps which is too much to run through the Arduino.

So I was looking for a way to power them through an external source but control them with the arduino. Similar to this:

6

You connect the Gnd of the supply to the Arduino Gnd and to the Gnd of the strip.
You connect the 5V of the supply to the strip.
You connect the signal pins to the Arduino.
Nothing else.

7

Connect as CrossRoads explained.

You DON't use mosfets with this DIGITAL strip.

DO use software for a DIGITAL WS2801 strip.
Normal PWM does NOT work with this strip.

A digital strip like this one can do much more than a common analogue strip.
With a common strip (the one that needs three mosfets) you can only set the colour/ brightness for the whole strip.
With a digital strip, you can change every individual LED to any colour/brightness you like.
And make coloured patterns, running lights, etc.

Lots of info on the net.
Here's one page.

Leo..

8

Wawa:
Connect as CrossRoads explained.

You DON't use mosfets with this DIGITAL strip.

DO use software for a DIGITAL WS2801 strip.
Normal PWM does NOT work with this strip.

A digital strip like this one can do much more than a common analogue strip.
With a common strip (the one that needs three mosfets) you can only set the colour/ brightness for the whole strip.
With a digital strip, you can change every individual LED to any colour/brightness you like.
And make coloured patterns, running lights, etc.

Lots of info on the net.
Here's one page.
http://www.tweaking4all.com/hardware/arduino/arduino-ws2812-led/
Leo..

Thanks a bunch CrossRoads and Wawa! This is essentially what I want to do then with Clock and Data on Digital 6 & 5 (unless I messed up):

(the reason I have the 2 strips connected is because I want them to run at exactly the same time from the same sketch)

So the problem I have now is what if I want to power the Arduino from the same 5V supply but that supply has to be close to 5A now. Can I just power it from the same source without some type of protection or resistance given its the same V?

9

I see no problem in powering the Uno from the same 5volt supply (connected to the 5volt pin).
Providing it's regulated, and never goes over 5.5volt.

A good regulated supply is important, because every LED on that strip has a chip with the same voltage limitations.

Best to disconnect the wire between the supply and the 5volt pin when you connect the Arduino to a computer.
You don't want USB supply to fight the LED strip supply.
Leo..

10

Thanks so much for all the advice you all. I guess I was trying to make it more complex than it really was.

11

Wawa:
I see no problem in powering the Uno from the same 5volt supply (connected to the 5volt pin).
Providing it's regulated, and never goes over 5.5volt.

Well if you do this, you'll need to ensure thorough decoupling, as its a high current supply.
0.1uF + 10uF + 470uF or so would be the sort of thing to use. In general you have an easier
time if you don't share logic and high current supplies. If you have long cabling runs you
should decouple at the strips themselves, and you'll need thick wires for high current low voltage
to avoid IR voltage loss along the cables.