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It works!

johnbeetem

I got my RasPi today!  It works pretty well, and I did not have much trouble bringing it up.  Since I've been watching and commenting here at element14 and in the raspberrypi.org Troubleshooting section for some time, let's see how my RasPi compares to her sisters:

 

1.  Before plugging my RasPi in, I checked the resistance of the polyfuses to see if they will deteriorate over time.  I don't have a proper low resistance meter which nulls out lead resistance, so these are approximate.  The main power fuse F3 was less than 0.2 Ohm.  The two USB fuses F1 and F2 were 2.0 - 2.2 Ohm.  I don't care about them, because I'll be using a powered hub.

 

2.  I'm using a powered USB hub to provide power to RasPi.  My power supply is based on a Linear Tech demo board and gives very reliable 5V which powers my USB hub.  The resistance from power supply GND to RasPi TP2 is less than 0.1 Ohm.  However, the resistance from power supply +5V to RasPi TP1 seem to be at least 0.5 Ohm.  My micro USB cable obviously has better GND conduction (probably a foil shield) than +5V conduction (1 meter of 28 AWG).  I think the +5V resistance is pretty well shared by the micro USB cable and F3.

 

3.  The procedure described at raspberrypi.org and the RasPi wiki for downloading Debian and copying the image to an SD card (GNU/Linux command line) worked perfectly.  It took a while to download 443 MB from the mirror and to copy the uncompressed 2 GB to a Class 4 SanDisk microSD card, but there were no problems.

 

4.  RasPi booted the first time (wow!), in spite of some power supply problems.  My power supply produces +5V from whatever 9V-12V wall wart I have handy.  The first one I used did not provide enough current for RasPi (it works quite well for BeagleBoard thank you very much) and this caused my monitor to be unstable, occasionally blanking out and showing green "static".  I switched to a more powerful wall wart and RasPi booted perfectly with no display problems.

 

5.  My particular RasPi seems to work with surprisingly low voltage.  When I get the login prompt my TP1-TP2 voltage is just 4.65V.  When I start up X Windows it drops to 4.60V.  I guess my peripherals don't need anything like the USB 4.75V minimum.  I'm using a NEC DVI-D monitor which didn't require any config.txt options, along with Logitech wired keyboard and mouse.  I'm guessing that these are all 3.3V devices and having 4.60V HDMI and USB voltages doesn't faze them.  The monitor is actually connected through a cheap "HDMI Switcher".

 

6.  I tried Midori and connected to raspberrypi.org to announce success.  Ethernet came up and automatically congfigured to my router just fine.  However, Midori did not run well -- normally consuming all compute time -- so I gave up.  I'm going to see if assigning the Level 2 cache to the ARM CPU helps.  GUI-based terminals and text editor were responsive and I had no problem writing and compiling "Hello, World" except that I need to set my keyboard to USA if I want to type any punctuation.

 

7.  My RasPi gets quite warm.  I wouldn't say blazing hot -- I can leave my finger tip on the SoC and LAN chip for several seconds.  The back of the board gets very warm.  I'm thinking of adding heat sinks and a thermal pad, but first I'm going to try mounting RasPi vertically so that air can flow past both sides.  I'm concerned that the high temperature will cause F3 resistance to increase, lowering my 4.65V down to something that makes the board fail.  This might be the cause of some of the "RasPi works for a while and then stops" posts we've seen in the Troubleshooting section.  I'm planning to put a low-resistance non-resettable fuse in parallel with F3 to prevent F3 problems.  This should get my 4.65V up to 4.8V, which is plenty.  If 5V0 gets too high, RG2 has to work harder and that makes the board hotter.  So I think keeping my present USB cable may actually help things.

 

8.  Yay, Debian already includes libXft.so!  That's the only unusual library I need to port my software.

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  • John Beetem wrote:

     

    8.  Yay, Debian already includes libXft.so!  That's the only unusual library I need to port my software.

    Well, Debian includes the executable for Xft, but not the development files (i.e., *.h).  "apt-get install libxft-dev" didn't work the first time.  It took a bit to figure out I needed to run "apt-get update".  Once I did, "install libxft-dev" worked fine and my software compiled and came up perfectly (well, except for some nits having to do with different fonts).

     

    All-in-all, I'm quite happy with RasPi's performance when running my software.  I don't need a lot of memory or graphics performance, and I don't have a lot of disk traffic.  So RasPi's limitations don't hurt my software.  RasPi seems slower than my 600 MHz BeagleBoard, but I really need to time it to be sure.

     

    Midori still runs very slow.  I tried turning off scripts, but it didn't seem to make much difference.  It just takes a horrific amount of time to scroll the screen (raspberrypi.org and element14.com).  I couldn't even log in at raspberrypi.org.  element14.com login succeeded, but I couldn't write this message using my RasPi.  OTOH, the Google Code page where my software sleeps and dreams loaded quite quickly.  I suspect the problem with the first two is that they try to write myriad files to disk (i.e., a class 4 SD card) and RasPi balks.

     

    With Ethernet disconnected, my vertically-mounted RasPi runs at a reasonable temperature.  With Ethernet active things get quite warm, especially doing Midori.  (The HDMI shell makes a nice radiator.)  I think I'd be better off with a Model A, with an Ethernet dongle to spread out the heat.  OTOH, it's easy to unplug Ethernet when it's not needed.

     

    So all-in-all, as long as I don't try to use Midori and heavy use of Ethernet, RasPi is quite an endearing little machine with wonderful capabilities for a gadget that small and cheap.

  • in reply to johnbeetem

    John, I'm wondering about your temperature "problems".

     

    My 'pi has been on for 7 days now. It's had time to warm up. When I put my finger on the SOC, it is just over the "comfortably warm" temperature. Maybe indeed I'd like to pull it away after a few seconds. But if I then put a different finger on there, the temperature has sufficiently dropped that I can keep it there.

     

    This is consistent with my measurement/guess that my fingers have a heat-carrying-capacity of about 1W (each) and the fact that my raspberry pi consumes 2.2W and divides that almost equally between the SOC, the LAN and the 3.3V regulator.

     

    Can you measure the powerconsumption of your 'pi? If there are large differences there is something wrong with the design. (We already know of one place that could lead to excessive power consumption, however I would have expected that in 99.99999 % of the cases this wouldn't matter. (as in not likely one of the few that are in the field today))

  • in reply to rew

    Roger: Your 1W fingers stirred a curious thought. image

     

    When we measure voltage we use a high impedance probe to avoid affecting the observed system.  Is there such a thing as a temperature probe with very low thermal conductivity and very low thermal capacity?

  • in reply to morgaine

    Yes. It's called an IR camera. The cheap ones measure the temperature at one spot.

    http://www.ebay.com/itm/Pocket-Digital-LCD-Non-Contact-IR-Infrared-Pen-Thermometer-Measure-Temperature-/180875324487?pt=US_Weather_Meters&hash=item2a1d026c47

    (last I looked the cheapest one was $15, apparently they've come down in price a bit... )

     

    the very expensive ones have a multi-megapixel camera and calculate the temperature for each pixel. You then get an image of what gets warm. The image is usually color-coded using "false colors".

     

    http://www.ebay.com/itm/VisIR-Ti-200-IR-Infrared-Thermal-Imaging-Camera-with-2-Batteries-Hard-Carry-Case-/300601841017?pt=BI_Cellular_Optical_Television_Test_Equipment&hash=item45fd441579

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  • in reply to rew

    Interesting (especially the very cheap pen one), but not what I was asking, which was about contact probes that work like your finger rather than non-contact thermal radiation detectors.

     

    Thermistors and thermocouples clearly don't have the properties I was asking about, but perhaps other contact probe types might have.