Maximum sustained current (and brightness)

kriegsman

Hi Blinkinlabs! I've got a question about the maximum current that the BlinkyTape is designed handle for sustained periods.

I noticed this line of code in your ColorSwirl sketch:
LEDS.setBrightness(93); // Limit max current draw to 1A

With the brightness set to "93", the ColorSwirl's default animation draws around 250mA (a quarter Amp). Changing the "93" to "255" in that sketch bumps the power draw up to 675-725mA.

With all pixels set to full-on white, and brightness set to the maximum of "255", the BlinkyTape draws 1.5+ Amps.

My question is this: what's the maximum current that the BlinkyTape is designed for handle for sustained periods? Is the "1A" comment in the code there more to preserve battery life, or is there an element of the BlinkyTape's electrical design that makes it a bad idea to run at more than one Amp for more than a short period?

Maybe to rephrase my question a bit: does the "+5" power line to the LED strip run directly from the USB port's +5 line, or does it go through a power regulator?

Thanks! I'm loving the BlinkyTape so far... and I'll be publishing some animations for it this weekend, I hope!
-Mark Kriegsman

Xan

I guess you know that well, but according to the standard most USB 2.0 host hardware won't provide more than 500mA and can forcibly power down if you try to draw more.

I know it doesn't answer your question, but just a relevant comment.

kriegsman

Thanks, Xan, and yes. I'm sometimes driving the BlinkyTape power sources that can deliver (more than) 2 Amps at 5 volts, e.g., an iPad charger, a lithium battery pack designed for 2A draw, etc.

For what it's worth, I'm measuring USB current (and voltage drop) with a PortPilotPro -- which I love. http://portpilot.net/portpilot-pro/ If you need fast, accurate, precise power info about a USB-plugged device (and you can justify the cost), this is the way to go. My next-favorite option is significantly cheaper, but not quite as nice: http://www.amazon.com/dp/B00DF2485S/

Xan

I understand that you can drive the BlinkyTape with more - but you don't want to end up with a situation when your firmware causes host hardware to disconnect it before you can reflash.

It's more of a warning for other people who might read this thread later.

kriegsman

Absolutely! And believe me, I've been there. These days, I start all of my high-current programs with a 3-5 second delay during which the strip is totally black, so I have a window to jump in and reflash if needed. I also most often have the brightness then ramp up from black to 'full power' over a several second period, as well, just in case. Plus, it often looks nicer than just WHAM! LIGHTS!

Matt Mets

The BlinkyTape can handle the high current, it will just get pretty warm. I would recommend making sure they are unrolled if you're going to use them like that. The biggest concern is the USB power draw.