I want to build/buy a VERY small computer

Discussion in 'Linux Hardware' started by Charles Reynolds, Jan 21, 2014.

  1. Charles Reynolds

    Charles Reynolds New Member

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    I've got a computer that's dedicated to a single task, and I'm trying to miniaturize it. I'm hoping you can offer some hardware suggestions.

    Here's what I currently have:


    An old laptop (refurbished ThinkPad T43, Pentium M processor). No hard drive, 1 GB RAM.

    Puppy Linux 5.5, booted from CD. (Prior versions of Puppy work also, at least as far back as 4.1).

    A device I'll call the “gadget,” which I can't discuss further (work related, confidential, etc). The gadget connects to the laptop by USB, and continuously outputs data via a 9600 FTDI COM port (/dev/ttyUSB0), although it's using only a fraction of the bandwidth. It delivers about 4 bytes per second of data, which works out to about 350 KB per day.

    A USB thumb drive, formatted for Linux, plugged into the laptop's other USB port, where the data from the gadget is stored.

    So I boot the laptop, mount the thumb drive, copy a few files from the thumb drive to /usr/bin and /usr/lib (execs and shlibs that Puppy doesn't have by default), and end up doing this:

    # cat < /dev/ttyUSB0 > /my_thumb_drive/mydata

    Then I leave it alone for a few days, after which I collect the data.

    Problem is, in its final form, the whole thing has to be put in a location where there's no line power available (and I can't use off-grid power sources either – e.g., solar cells). And I don't know of any laptop batteries that hold several days worth of power.

    So, here's what I need:

    First – and this is what I need help with from you – some very low power thing, let's call it the “micro-PC,” that will boot and run a very minimal Linux. It doesn't have to have a network card, keyboard, monitor, etc. Just two USB connections.

    Second, a very chopped down Linux that will boot from a USB thumb drive and automatically collect data as described above – I can handle that part fine.

    The idea would be that I would plug the thumb drive into the micro-PC's USB1, the gadget into the other USB port, and power the thing on. It would boot from the thumb drive, then automatically collect the data from the gadget and store that data in some file on the same thumb drive. The whole thing would run on ordinary batteries (I'm thinking of rechargeable D cells). And it would run, unattended, for several days. At the end of that time I'd power it down, swap the thumb drive for an identical one, swap the batteries if necessary, boot it again from the new thumb drive, and take the old thumb drive back to the office with me where I'd work with the data, etc.

    Now, what do I use for the micro-PC? Any suggestions? I'm pretty clueless on such things – the only two things I've been able to find with web searches are thin clients and Arduino, neither of which seem to be what I need. And if others out there have had to do something similar and can recommend good hardware, I don't want to re-invent the wheel.

    Thanks,

    Charles
    |)/-\|) likes this.
  2. Videodrome

    Videodrome Active Member

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    I don't have a lot of experience with this, but my brother recently bought an Android-based mini-PC. He uses a model with HDMI output to hook up to his TV for web browsing.

    I tend to doubt this will boot USBs, but who knows. On the other hand, maybe this tiny thing could run your software on the host and just write to the USB?

    [​IMG]
    Yesyesloud likes this.
  3. grim76

    grim76 Active Member Staff Writer

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    What about a Raspberry PI or something similar?
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  4. arochester

    arochester Well-Known Member

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    I think that might be a major problem if you intend to run off-line. Batteries, battery packs tend to run for hours not days.
  5. grim76

    grim76 Active Member Staff Writer

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    They can run for days under the right circumstances. Minimizing power draw and such you can get a battery pack to run you for a day or so.
  6. |)/-\|)

    |)/-\|) Member

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    Sample rate is probably the key to power consumption in your case. Without more detail about the device you're driving (does it cycle sample or continuously operate, is it smart or dumb?) it"s hard to know how much on site processing needs to be done.

    On battery power, less is more. Batteries love heat, silicon loves cold. Neither likes moisture. Do you really need linux at the remote?

    Look at Intel, PIC, NEC, TI. They all produce development boards. Look at e-book reader batery life expectancies. My old NOOK Color still has enough charge left in it after a week to wake up and use for 30 minutes (reading 15-30 min a night). That's a TI chipset running Andriod (it IS TOO linux with Java running in the middle!) with motion detection, etc. (the mini usb port is for chargeing).

    Or you get run your current system on about 12 car batteries :rolleyes:
    Last edited: Jan 21, 2014
  7. Charles Reynolds

    Charles Reynolds New Member

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    Thanks for the suggestions! Both the Android mini PC and Raspberry Pi look like they could be workable. I'd heard of both of them before, but only in passing – I'd never needed something like this before so I didn't pay any attention to them, and assumed that they were more power-hungry than they appear to be. I haven't finished digging into things yet, but as of now the Raspberry Pi Model A (the low power version) looks particularly promising.

    When Googling for “raspberry pi” I found this page by someone who's been down the same road (well, sorta), a guy who sends them aloft on balloons:

    [EDIT -- It seems that as a brand new user, I can't post a link yet. Oh well. If anyone really wants the link, send me a private message.]

    I'm a little skeptical of some of his numbers, but assuming he's in the ballpark it looks like I might be able to pull this off with some NiMH D-cells and a voltage regulator … although leaving it alone for “several days at a time” might have to be changed to “a day or two.”

    > Without more detail about the device you're driving (does it cycle sample or continuously operate, is it smart or dumb?) it"s hard to know how much on site processing needs to be done.

    Well, as I said, some of this I can't talk about. But I've been told (and haven't confirmed it) that the device draws about 40 milliamps. In return for that it bleeps 3-4 bytes per second over the USB connection. There's no data going out to the device, everything is incoming, and the only thing that needs to be done is to collect the incoming data and store it on a removable storage device (which doesn't specifically have to be USB; e.g., a micro SD card would do).

    > Look at Intel, PIC, NEC, TI. They all produce development boards. […] Do you really need linux at the remote?

    I've glanced at PIC's development boards before, but never the others. If the others are anything like PIC, I'd rather not go there just for this project – the things look intriguing, and they're on my list of “stuff to try some day” and have been for some time; but I'd be starting from “completely clueless newbie” if I tried working with them. It doesn't absolutely have to be Linux but for a lot of reasons (including “office politics”) I'd rather do it that way if possible.
  8. grim76

    grim76 Active Member Staff Writer

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    How much space are you working with?
  9. |)/-\|)

    |)/-\|) Member

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    You could always just use linux for download / processing. I was hinting more at assembler for the field piece. Use nonvolatile RAM for raw data storage and massage it on desktop. Then with the time you save not using an OS in the field you could run a a much lower clock speed on the MCU which saves power (high clock speed sucks power).

    Conversely, you could run MCP at very high rate and sample each bit then power down till next bit comes in, but this requires careful syncing in order to meet byte and bit timeing.
  10. unixfish

    unixfish Member

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    I think the important question here was from grim76 - How much space are you working with? If you have space available, you could put a car battery with the proper converters and use a Raspberry Pi and probably run for weeks. I will state the obvious here - make sure your power converter is good because that battery could melt your whole setup into a pile of plastic and glass.
  11. Charles Reynolds

    Charles Reynolds New Member

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    > How much space are you working with?

    It all has to fit in a box that's 8” X 12” X 18”. The gadget is maybe 1” X 2” X 4”, I haven't even bothered to measure it. As long as I can get away with rechargeable D cells or something similar (and I've seen some for sale with 10000-12000 mAh), I don't think space will be a problem. If I have to go to something like car batteries, that might be a different story.

    Also, the environment will always be dry, ordinary air humidity, room temperature, no direct sunlight, and well ventilated, so at least I don't have to worry about anything along those lines.

    > You could always just use linux for download / processing. I was hinting more at assembler for the field piece. [etc]

    Well, this thing isn't being developed for sale to the general public, it's an ad hoc thing to collect data for a research project. The sort of thing you're talking about would consume less power, I suppose, but the solution doesn't have to be the best one along those lines, it just has to be good enough. But it also has to be comprehensible to the people I work with, including that if I'm struck by lightning they need to be able to pick up where I left off and even modify it if necessary. I'll do something like this if it becomes absolutely necessary, but I'd much rather keep it as simple as possible and add more batteries if I have to.

    > I will state the obvious here

    LOL -- No offense taken. :)
  12. |)/-\|)

    |)/-\|) Member

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    If money no determent then lithium-ion batteries series-parallel to get 18 volts (haven't calculated Ahrs to = 40 W) would let you keep the Thinkpad. Just use every power saver setting on pc (especially to get that screen turned off) and you should be able to run for a couple of days without a harddrive. The small Thinkpads ran pretty long with a small stock battery pack (had 1 at work years ago).

    Have fun with it.;)
  13. Charles Reynolds

    Charles Reynolds New Member

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    > Have fun with it.;)

    I will. I've already ordered the R-Pi A, and even if I end up not going that route for this project it looks like it will be interesting to play with.

    It may be a while, but I'll post a summary here of whatever I come up with.
    |)/-\|) likes this.
  14. Yesyesloud

    Yesyesloud Active Member

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    Raspberry Pi is overrated, it is for many 'hardcore custom build' enthusiasts what iPhone is for apple fanboys (pardon the hilarious analogy). It's ok, it's 'mainstream' among the tech savvy, and I'd simply advise against it, because I have tested really many devices with ARM CPUs. In my opinion, despite its lack of proprietary video driver for Linux, the most cost-effective chip right now is RK3188 (4 cores at clocks as high as 2Ghz, with built in mali quad core 533Mhz gpu). Its GNU/Linux performance is amazing and I find it much more responsive than that Raspberry dinosaur.

    Upon little research, you can have a RK3188 device like that with 2 GB DDR3 RAM and 8Gb storage for less than $60. Better, huh? It's not more expensive at all if you compare the specs. Just make sure you get one with a RJ45 port if you want to run a Linux distro, since its wireless support is not that great outside of Android. Look: http://goo.gl/4FdjOD (wifi network though)

    To the moderators, I apologize beforehand for linking a store, it was for the sake of an example, and good cheap stuff can be of public utility. People talk about broadly known commercial brands (like Raspberry) all the time, that kind of 'inoffensive' publicity is more effective and worse SPAM, but just edit the link out in case there's any problem. :)
    Last edited: Jan 24, 2014
  15. DevynCJohnson

    DevynCJohnson Well-Known Member Staff Member Staff Writer

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    What about the Cubieboard which is more powerful than the RPi, but a little more expensive (~$99)?

    http://cubieboard.org/
  16. ryanvade

    ryanvade Administrator Staff Member Staff Writer

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    MicroATX board, Cheap intel/amd cpu. a little ram. As small of a case as you can find. :)

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