Comment by perlin | Hacker News Reader

Comment by perlin | Hacker News Reader

We've actually found that the RPi doesn't draw enough power, specifically to the USB ports. Our peripherals are within the USB spec of a 500ma max pull, but even so we are experiencing sporadic CPU brownouts. The first thought was to double the max_usb_current in /boot/config.txt, but that only lengthened the time between brownouts. We looked into hacks that could increase the current even more, such as this bypass method: http://hackaday.com/2015/04/06/more-power-for-raspberry-pi-u.... Unfortunately, this isn't a viable solution as we continue to scale up our deploys. Some viable alternatives include switching to a board that supports USB3.0, underclocking the CPU, or doing a custom solution through Element14. I really wish the RPi was more stable around power / fault tolerances, but they're a blessing nonetheless :) [Plug]: If you're based in NYC, enjoy hacking hardware and find these types of problems to be delightful, please shoot me an email: mykola@colorcreative.io ;)

It is normal that you are experiencing brownouts if you assume 500 mA is available.

If you power a RPi via micro USB, then the 500mA budget is shared between the RPi and all your peripherals. Your post doesn't say which RPi model you have, but a B+ or a gen2 B will draw anywhere from 230-420 mA idle, so your periphals only have 80-270 mA available.

[1] http://www.midwesternmac.com/blogs/jeff-geerling/raspberry-p...

Have you tried a BeagleBone Black or any kind of BeagleBoard? What are you scaling RPi's for? Arduino and Raspberry pis strike me as toys compared to BBB's. BBBs are a lot less forgiving and require way more understanding of basic electronics to do anything with, even as simple as lighting an external LED will break your BBB if you didn't do it right, but they seem more powerful in terms of what you can do (although underpowered compared to Rasbperry Pi when it comes to video processing).

I have plenty of experience frying BBBs while trying to make LEDs blink ;) http://colorcreative.io/portfolio.html. The reason we use RPis in my place of work is due to USB peripheral support. I love the dedicated PRU in the BBB, though. It's perfect for the tight timing spec required by the WS281x LEDs :)

Wait, how can you break the BBB with a LED? I'm going to use one for a LEGO robot, and I'd like to not fry it :P

Our team has personally blown through three of them through shorting faults. It's our fault, but the BBB is a pretty tender beast.

That's too bad, it's pretty pricy :/ It's no $2 ESP8266, I wouldn't feel very bad shorting that, but at $70, I'm going to be super careful with my BBB.

The gpio pins have low tolerance. Apply more than the 8mA or 3.3v and you permanently damage your board. LED's usually require 20mA to achieve a good brightness so you have to create a safe circuit using a bipolar transistor and the 3.3v power pin which supplies way more current than a gpio pin. If you hook up that transistor wrong or short the circuit it's game over.

I actually think you can even damage the board if you create a short between the gpio pins and ground. So any kind of circuit requires a resistor, carefully reading the system manual and data sheets for your components and using ohm's law prior to hooking up components.

That's good to know, thank you. I'll have to only drive the MOSFETs with it, in that case, and avoid too much experimentation.

Oh I wasn't saying not to use a bipolar transistor. In any case, both would work. Good luck!

Oh, no, I need the MOSFET anyway because of the load. I generally meant "I'll avoid unknown components/experiments with the BBB", thanks!

Also, make sure you set the max_usb_current setting to 1 to provide more juice to the ports (see: http://raspberrypi.stackexchange.com/q/27708).

Splice your power supply directly across to the USB cable of the thing you're driving. For the Pi Zero, use an OTG+power cable. I think you can get cables with two A connectors (one for power, one with data+ground but no VCC) and 1 B connector.

I'm not interested personally, but your HN profile doesn't seem to include any contact info.

thanks for pointing that out. I've updated the OP to add that + correct the typo pointed out below

Depending on your requirements a powered USB hub could solve your problems quite nicely.

Also, having a good power supply makes a big difference. I have 2 RPIs running OSMC and used to suffer random lockups/reboots/corruption using a random power supply. Once I switched to a decent supply, they have been rock solid.

Hey, I poked around your website and like what you do! I'm a tinkerer too and have messed with LEDs and mirrors, but was wondering if you've heard of HeavyM [1]? I enjoyed a lot and it looks right up your alley. It uses a projector for cool visual stuff.

Also - get wordpress and analytics.

[1] http://heavym.net/en/

I thought USB 2.0 had 500ma max current?

indeed, you are correct https://en.wikipedia.org/wiki/USB#Power

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