Thursday, January 24, 2013

Raspberry Pi Model B to Model A Conversion Cleanup - Part 2

Be sure to see part 1. A lot of the components on the board are now redundant as they are no longer used/connected, so for cosmetic reasons we can now remove these from the board. The easiest way to remove them is to load a soldering iron tip with solder and flood the SMD components. They should just flow away and join with the solder lump on the tip and leave a nice clean finish.

Firstly on the top, you will want to remove the components in the spaces marked red. You can also remove the RJ45 connector if you wish.


On the flip side, you can also remove the SMD components marked in red. The crystal might be a little difficult to remove, but as before if you don't want to re-purpose it, you can just load it up with solder and keep the heat on it until it slides away. Otherwise you can use the same technique used with the gas torch:


Now you can remove the USB connector and change it with a single port variant.


You will now have an almost indistinguishable Model A Raspberry Pi.
Why all the fuss you might ask? Well lets have a look at some figures for the 512MB "Model A" Raspberry Pi.

Power usage comparison with the other Raspberry Pi models (the Model A here is the original pre-production model).

From the page:
352mA - Model-B Running stress test
330mA - Model-B Idle
143mA - Model-A Running stress test
118mA - Model-A Idle (with HDMI connected)
110mA - Model-A Idle
107mA - Model-B After "sudo halt"
33 mA - Model-A After "sudo halt"

From my tests with the 512MB Model A with a lab supply at 5.00V:
35.29mA - After "sudo halt"
106.9mA - Idle (avg)
111.1mA - Idle (avg) (with HDMI connected)
163.5mA - Running stress test
165.9mA - Running stress test (with HDMI connected)
265.2mA - Stress Quake 3 (avg) (with HDMI connected)

My CPU stress test was run with:
cat /dev/urandom |gzip > /dev/null & md5sum < /dev/urandom &

It looks like it draws a little extra current while stressing over the 256MB Model A. This would undoubtedly be due to the doubling of the RAM.

Update:

Juggling with RAM sizes by giving 256 to the GPU and 256 to the CPU (in /boot/config.txt) yields the following:
160.6mA - Running stress test
163.5mA - Running stress test (with HDMI connected)

5 comments:

  1. Hi
    Would it be possible to add switch to control Ethernet chip on/off? Or use GPIO pin with transistor.

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    Replies
    1. You could, but if you don't need USB, you can actually just do it in software by disabling the USB port on the SoC.

      Do this in raspian with the following:

      echo 0x0 > /sys/devices/platform/bcm2708_usb/buspower

      You could connect a switch up to the GPIO and write a script which triggers that when it's been flicked. To turn it back on the script should echo 0x1.

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    2. But this will shut down all eth/usb or lets lower usb still working?

      (I suppose shut downs all, because otherwise you will need to link R36/37)

      buspower will be 0x1 after reboot or keeps written value?

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    3. Yep both. It will reset when the raspi resets.

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  2. One more reason to the 'Why all the fuss' part is that you can get lower side profile in your RPi. Much lower if you get rid of the video out connector, too. Depending on your needs you can either by just remove the connector or replace it with something similar to the audio out connector.

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