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It works!

johnbeetem
johnbeetem over 13 years ago

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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  • morgaine
    morgaine over 13 years ago

    Gratz John! image

     

    I'm eagerly reading your experiences, the more fine details of voltages etc the better.  That has been somewhat missing from startup reviews thus far, so I'm very glad to see it.  And measuring the polyfuse resistances before applying power was an excellent idea.

     

    Still waiting for mine ...

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  • Former Member
    Former Member over 13 years ago in reply to morgaine

    John,

      There seems to be a surprising amount of variation between what people

    are reporting.   You seem to have relatively low resistance F1 & F2 compared

    to 5 to 8 Ohms reported elsewhere.  Your temperatures are consistent with

    others who have said 5 seconds is all they can touch the SoC & Lan chips,

    but then other people report closer to body temperature.   Your 4.6V between

    TP1 & TP2 seems lower than some people report, and I think will cause

    flakiness with various power supplies (as you have already seen), and SD cards,

    and USB devices.  Some people report that 4.8V is not enough.

     

    I wonder what's causing such large variations?

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  • morgaine
    morgaine over 13 years ago in reply to Former Member

    Someone with a hot Pi must have an infrared imager too ...

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  • morgaine
    morgaine over 13 years ago in reply to Former Member

    Someone with a hot Pi must have an infrared imager too ...

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