Neopixels & regulators

[AndyB871]

So We're toying around with the idea of using Adafruit's neopixels for some fun projects this year, I know other teams have done similar things, and I'm also aware of the rioDuino MXP widget.

That being said, I'm concerned about total current draw and where to source that current. The large neopixel strips can draw upwards of 4 amps. The VRM can only source 2A, Plus the neopixels are finicky about having a common ground between the data signal and power supply.

My Question is this:
If we were to use an arduino as a coprocessor to control these strips, does anyone have any reccommendations for legal 12V-5V >4A DC-DC regulators? Ideas how to ensure that power supply ground & arduino DIO ground is connected?

I'm a Comp-Sci Guy, I've only lightly dabbled in EE, so while I "understand" this stuff, I'm not as fluent as Id like to be (obviously)

Thanks!

[Knufire]

What about the voltage converter that powered the radio on the old control system?

http://www.andymark.com/product-p/am-0899.htm

[orangemoore]

Originally Posted by AndyB871

So We're toying around with the idea of using Adafruit's neopixels for some fun projects this year, I know other teams have done similar things, and I'm also aware of the rioDuino MXP widget.

That being said, I'm concerned about total current draw and where to source that current. The large neopixel strips can draw upwards of 4 amps. The VRM can only source 2A, Plus the neopixels are finicky about having a common ground between the data signal and power supply.

My Question is this:
If we were to use an arduino as a coprocessor to control these strips, does anyone have any reccommendations for legal 12V-5V >4A DC-DC regulators? Ideas how to ensure that power supply ground & arduino DIO ground is connected?

I'm a Comp-Sci Guy, I've only lightly dabbled in EE, so while I "understand" this stuff, I'm not as fluent as Id like to be (obviously)

Thanks!

Try the old KOP 12v -> 5v converters. Those things should work just fine and you should probably have some lying around not being used.
http://www.andymark.com/product-p/am-0899.htm

EDIT:Ninja'd

[billbo911]

Using a simple UBEC/BEC that are commonly found in the R?C hobby, you should easily be able to strings of NeoPixels.

First, calculate the current draw with every pixel running full brightness and white. Then double that to find a suitable BEC to use. That level of safety margin will just about guarantee you will not have an issue with the BEC overheating.

[RyanShoff]

We ran 150 neopixels off the 2A VRM output without issue last year. It was a 5m strip 30 leds/meter. We never used all white full power, but otherwise took no special precautions. Grounding was not an issue. We grounded one end of the strip to the VRM and the other to the Roborio. For reference, the same programming would brown out the Roborio 5V supply.

[AndyB871]

*facepalm* I'd totally forgotten about the old regulator. we DO have a bunch of them laying around...

Well thanks for the quick replies!

[Greg Needel]

The other important thing to remember is what affects current draw. Each led Pixel is made up of 3 small LED dies - Red, Blue, & Green. If you put them on full power each die can draw around 20 mA, so 60mA per pixel max. This does add up, but odds are you are not just going to make an all white strip all the time.

If you do simple things like sweeps of single colors at a 50% duty cycle (which is still very bright), you can actually get away with driving the LED's off the VRM or even just the 12-5v regulator on the RIOduino/ arduino. It is easy to bench test this as you will see the LED's not work as expected and likely the arduino will restart if you pull too much current.

Last season we drove our LEDs directly off the regulator as described, but yes having a 12 to 5v regulator just for LED's is a good idea. The one for the old radio is a good option, but it is also very heavy. I have bought many of these http://www.amazon.com/KEEDOX%C2%AE-C...dp/B00A71CMDU/ They are light, cheap, and work great.



As a side note, while LED's on robots can be awesome looking and add some awesome bling, please keep it within reason. I also challenge teams to use the LEDs on their robots for practical things like indicators for drivers instead of just bling.

[Thad House]

Note the old KOP regulator has a fairly high dropout. We used one in 2014 to power our lights, and everyone at competition kept asking why our lights would randomly flicker and turn rainbow. It was because anytime we would start moving the voltage would drop to 8 volts and the regulator would brown out. We used these this year, and they were much more reliable. http://www.amazon.com/NEEWER%C2%AE-U...eywords=bec+5v

[BenGuy]

On our robot this year, we used an Arduino to control two 60 led strips, and we are using the two VRM ports power on it. Also, we have an inline resistor to the signal cable and a capacitor in line to the strip power cables to smooth out the voltage/current. Works perfectly.

[Joey1939]

Originally Posted by AndyB871

That being said, I'm concerned about total current draw and where to source that current. The large neopixel strips can draw upwards of 4 amps. The VRM can only source 2A, Plus the neopixels are finicky about having a common ground between the data signal and power supply.

We had two strips of 59 neopixels (long story) on our robot last year. We powered them off of the old radio 5V convertor without any troubles. We were also concerned about the shared ground but didn't experience any problems without connecting the grounds. The Arduino was powered off the USB port on the RoboRIO which lets us also send serial signals over USB.

[InFlight]

We used separate power supplies for the Display processing and LED displays. 2A for the processor and separate 9 amp supplies for the display. Any high demand by the display doesn't brownout the processor that way.

You can search on 3574 here if you want more design info on some over the top LED usage. The 2014 and 2015 robots where both fairly unique.

[Chadfrom308]

Don't even go to the old DC-DC converter. Since it's decoration (at least this was the case in 2014) you can use anything you want to power these things. Seriously all you need to do is look on hobbyking.com for a BEC. There are like 20 of them that output 5a @ 5v. That should be more than enough. And if you need more, you can get a Castle Creations 20a 5v (If you need this you are doing things very wrong).

And the best part is that they weigh under an ounce! I have ran plenty of neopixels on these guys before. They work perfectly every time.

If you don't like hobbyking for some reason, you can always search up on pololu or amazon for a 5v BEC or Buck converter. Super cheap and light stuff (Unlike the old dc-dc converter)

http://www.hobbyking.com/hobbyking/s...dProduct=62640

(Note: They may have changed the rules for this upcoming season. I am sure you would be fine ordering these, but still make sure they are in the rules

[feverittm]

Since people are talking neopixels and arduinos on their robots. Anyone care to comment on the code required to communicate between the roboRIO and the arduino to control the LEDs (on both the Arduino and the roboRIO please)? Serial or I2C communication? Independent Arduino or an integrated device like the roboDuino?

Thanks

[Thad House]

Originally Posted by feverittm

Since people are talking neopixels and arduinos on their robots. Anyone care to comment on the code required to communicate between the roboRIO and the arduino to control the LEDs (on both the Arduino and the roboRIO please)? Serial or I2C communication? Independent Arduino or an integrated device like the roboDuino?

Thanks

We just used a regular arduino, connected directly to the roboRIO using a USB cable. That both powered the arduino and gave a serial connection between the 2. From there, the easiest way is to send simple commands over serial to the arduino, and have the arduino use those commands to change the lights.

[Chadfrom308]

Originally Posted by feverittm

Since people are talking neopixels and arduinos on their robots. Anyone care to comment on the code required to communicate between the roboRIO and the arduino to control the LEDs (on both the Arduino and the roboRIO please)? Serial or I2C communication? Independent Arduino or an integrated device like the roboDuino?

Thanks

You can use anything. You can send a pwm signal to it and have the arduino read the pulse width, you could have just a simple on and off line going to it, you can have an I2C (which is much more reliable on the roborio), you can have CAN shield and attach it to the network, you can use serial, you can use ethernet. Whichever seems the most viable to you. I say use the one you know the most