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Possible Hardware fixes

Former Member

So one of the things I plan to do when R-Pi are more available is to butcher a couple of them and incorporate some things I consider to be appropriate hardware fixes. This is my list so far, any feedback or additional suggestions welcome.

 

1. Remove the SD Card slot and replace it with a small adapter pcb containing a micro-sd connector. The full size SD card sticking out the end is ok for development or when you want to swap the card a lot, not so good when you want to build the whole Pi into something else and would like to use some of that dead space for other things. 1764377 micro-sd connector chosen, will be oriented at right angle to the current slot.

 

2. Replace usb polyfuse arrangement. Diodes Inc AP1212 seems to fit the bill. 1825303 33 pence each

 

3. Replace RG1 & RG2. Current plan is to use the TPS54231 1755637 as suggested by jamodio, however it's relatively expensive. Also looking at AP1533, 1825334 which appears similar from an external components point of view, but approx 1/10 the cost.

 

4. Cut the 1.8v from the Lan9512. Could do with the full gerbers to work out if this is possible. C29, C36 & C43 along with pins 15 & 38 just vanish into vias. Ideas welcome.  My other options are to remove the Lan9512 and make myself a model A, or to leave RG1 off and see if we still boot with 1.8v from the lan9512 regulator.

 

5. As I'll be replacing the SD card slot, I'm contemplating if it's possible to add some power switching to allow running the slot at 1.8v to get some of the faster access modes. I think this will probably need some driver work and stealing a gpio from somewhere. I'd be tempted to use GPIO5 or GPIO27 (CAM_CLK, CAM_GPIO), but maybe the GPU will mess with those and GPIO31/CONFIG3 could be a better choice.

 

6. RTC based on MCP79410, 1823155

 

7. Removal of micro-usb power connector as I don't consider it appropriate. 5v and 3.3v can be supplied via P1 instead.

 

If only 1.8v was available on P1, some things could have been easier. So...

 

8. Replace P1 with a 28 pin connector to allow 1.8v to be made available. The extra two pins to extend off the end on the pcb and be wired to RG1's previous position.

 

9. For ease of integration, put P1 on the underside of the board and likely also replace P4 & S7 with headers allowing their connectors to be moved onto the underlying board and aligned better wrt case.

 

Thoughts ?

Parents

  • looks like a good list.  Too bad the PoP ram is so hard to replace,

    as that would be another nice improvement.  I've been thinking of

    modifying one for high-altitude balooning, or similar uses, where

    size and/or weight matter.  So here's my list:

      1) remove csi connector,

      2) remove dsi connector,

      3) remove hdmi connector,

      4) remove RCA connector,

      5) remove audio connector,

      6) remove ethernet connector,

      7) remove micro usb connector (directly solder power wires),

      8) remove GPIO pins,

      9) remove LDO voltage regulators, replace with switch mode,

    10) remove LAN chip,

    11) remove dual-usb connector, directly solder one usb device,

    12) remove polyfuses, replace with 1 Ohm resistor,

    13) remove the capacitor that frequently falls off,

    14) as you suggest, replace SD with micro SD.

  • in reply to Former Member

    I'll be replacying the polyfuses with 0 ohm resistors, no need ot waste power.

     

    I'll probably keep ethernet and HDMI.

     

    Agreed with the two FPC connectors, good move by RPF to offer a camera that will be more expensive than the board.

     

    The RCA jack takes too much space, same as audio, perhaps something done on similar designs like Roku2, replace both by a single jack that can carry all signals, but resolution and image quality out of the composite video output is not very good, perhaps better use something that can support VGA instead.

  • in reply to jamodio

    the 1 Ohm resistor is to avoid voltage drops from

    power surges on the USB device.

  • in reply to Former Member

    For that you should have a pair of good tantal bulk caps as recommended by the USB spec sort of 150µF, and I'd add USB power switches.

     

    I'd be nice if Broadcom started selling the "alpha" boards :-)

     

    -J

Reply Children
  • in reply to jamodio

    and I'd add USB power switches.

    I probably didn't make it clear enough in the list, the AP1212 I mentioned is a usb power switch.

     

    Making the obvious comparison, the cheapest 140mA polyfuse from farnell is 0.113 gbp in qty 5, and the AP1212 is 0.33 gbp in qty 1. So I'm not at all sure the case for using polyfuses is a good one. Don't know what costs @ 10K, 100K etc would be like though.

     

    Anyway, remove D10, D11 and both polyfuses and it should be simple to put the power switch in, the datasheet suggests a 33uF cap on the usb connector side and it has a soft-start feature to avoid the power dip when connecting a device.

  • in reply to Former Member

    Ohh you right I missed that one.

     

    Cost and the fixation on the credit card size form factor are very lame design guidelines, It is not bad to have an approximate target size, but they didn't have any mechanical restrictions or requirements, so component and connector layout could have been much better.

     

    -J