Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Raspberry Pi Zero – Conserve power and reduce draw to 30mA

midwesternmac.com

Post reply on HN
Print view View original

81–90 of 90 posts

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#81

Post by petra »

roymurdock wrote: post #56
petra wrote: post #34

Earlier quoted context omitted.

In general the mbed has the better options for low power , but if you prefer the arduino, this would be a good starting point: http://jeelabs.org/tag/lowpower/ And if you want a long-range, low-power wireless connection - use LoRa , There's a driver here: http://www.airspayce.com/mikem/arduino/RadioHead/classRH__RF...

How have you found the mbed OS tools/community/documentation to be? I've played around a bit with Arduino but I'm interested in checking mbed out.

In general Arduino definitely leads in documentation. The mbed community is smaller , but on the other hand more professional - so stuff would be of higher quality , less bugs , etc - but somewhat more complicated. Same goes for the tools - more complicated but more capable. If you're aiming towards something professional/startup/etc - mbed is the way .

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#82

Post by lemevi »

StavrosK wrote: post #50
lemevi wrote: post #9

Earlier quoted context omitted.

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…

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

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.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#83

Post by StavrosK »

lemevi wrote: post #82
StavrosK wrote: post #50

Earlier quoted context omitted.

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

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…

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.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#84

Post by lemevi »

StavrosK wrote: post #83
lemevi wrote: post #82

Earlier quoted context omitted.

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…

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!

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#85

Post by StavrosK »

lemevi wrote: post #84
StavrosK wrote: post #83

Earlier quoted context omitted.

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!

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#86

Post by Dylan16807 »

kwhitefoot wrote: post #42
janjongboom wrote: post #25

Why are we even using a Raspberry Pi for battery powered projects... 30 mA draw is so high you'll be changing batteries every 2 days, and that is without doing anything. Compare that to f.e. a normal phone chipset with deep sleep, which draws about 9 mA with a cellular connection, or .1-.2 mA in flight mode. Or, if you just use the Pi for sensor readings, get a proper microcontroller, where current is measured in mic…

That's what people who don't own smartphones say about smartphones.

Smartphones last as long as dumb phones if you turn off background data transfers.

So it spends part of the time being highly capable, and part of the time sleeping with no downsides.

The Pi is just not cut out to be a passive battery-powered device.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#87

Post by agumonkey »

ZenoArrow wrote: post #40
agumonkey wrote: post #37

Earlier quoted context omitted.

I thougth you were thinking of ~dumbphones, but sure enough any smartphone these days is exceptional in most features. Just today I saw a chinese dual core smartphone phone for 34$... The thing is that unless you're already in the know you can't repurpose the board. ps: funny, just an hour ago I was trying to flash an old nexus s with CM*.

> "The thing is that unless you're already in the know you can't repurpose the board." That's why projects like Fernvale are potentially very useful, as they would make it easier to repurpose the cheap hardware used for feature phones: https://www.youtube.com/watch?v=hpEqDPYtf9s https://github.com/xobs/fernly

I heard Bunnie was a master but the FPGA cpu MITM had me sitting down. Fantasy level impressive.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#88

Post by chatman »

weland wrote: post #70
chatman wrote: post #23

Why are you referring to the units of mA for "power", as opposed to current draw? The power consumed would be measured in watts or milliwatts.

When studying power consumption for this type of devices, it's extremely common to measure the current being drawn, rather than to put out values in watts. For one thing, it's the current that you usually measure in these cases anyway. For the other, power consumption in watts is not what you generally want to know when you design a battery-powered circuit. And, last but not least, it's more useful to have a figure i…

But the mA units were used in a table whose column heading said "Power saved". No matter what is "extremely common to measure", but it cannot be put in a wrong heading.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#89

Post by fanf2 »

akerro wrote: post #52

Ok, it has low power consumption... no eth, no wifi, no usb... how do you communicate and what for? Running on batteries for two days and manually coping data from sd card?

It does have a USB OTG port. In principle it should support device mode, but currently the kernel has it forced off to avoid interop problems, and if you fix that the driver is known to be buggy. But if device mode can be made to work then you can use USB gadget drivers such as g_ether to communicate with a bigger computer using just a USB cable - make a cheap alternative to a USB Armory, perhaps.

Re: Raspberry Pi Zero – Conserve power and reduce draw to 30mA

#90

Post by robzyb »

langarto wrote: post #39
robzyb wrote: post #24

Earlier quoted context omitted.

The Raspberry Pi runs on a fixed 5 volts. At a fixed voltage power will scale linearly with current.

That's a poor excuse for not using the correct terminology or the correct units.

It wasn't intended to be an excuse for not using "correct" terminology or units.

The reason that these terminology and units were used by OP was because at a fixed voltage it is common for engineers to think about current instead of watts... even when their aiming to reduce power.

I'm not sure of the exact reason for this, but I suspect that it's because:

a) Measuring current is a more fundamental function of instruments. Quite a lot don't even measure power. So talking about current instead of power, even when you're aim is to reduce power, makes for a smoother process from a practical sense.

b) Batteries are usually measured in mAh. At lower power/currents you're usually using a linear regulator and therefore dividing mAh by mA is a very important measure. So you often keep everything in mA.

Post reply on HN