Gp2x Mk1 Bob


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Joined
Dec 7, 2005
Messages
127
Content
-Intro
-Reasearch
-The mod
-Questions

Intro
During the weekend I have been doing some research as to why the MK1 GP2X cannot power the BoB, in order to find a solution.
Currently (without any modification) the (or at least my) MK1 BoB situation is like this:
-Connecting the GP2X to a unpowered BoB results in a GP2X failing to boot with a distorted screen (same as with empty batteries).
-Connecting a unpowered GP2X to a powered BoB immediately activates the GP2X (regardless of the power switch) and results in a GP2X which fails to boot.
-Connecting a powered bob to a powered GP2X works, but the power must be applied in the following order (GP2X, BoB). The GP2X will fail to boot at first, but appears to be reset when the BoB is powered. The GP2X then boots successfully.

Research
I've looked into things and came to the following conclusions.
-Pin 20 and 21 of the EXT connector (the 3.3V pins) are connected to ground on the BoB though 2 capacitors (C15 and C43). (Why?? -> See questions.)
-Pin 19 of the EXT connector does not appear to be nRESET. When the BoB is connected to a booted GP2X the voltage on this pin is 3.3V. (Anyway, is nRESET outgoing or incoming? -> See questions.)
-Pins 20 and 21 of the EXT connector on the GP2X are directly connected to its internal power circuit (the output of the DC/DC converter).

Mod
The BoB can easily be modified to be powered from a MK1 GP2X. All it takes is a connection from the 3.3V lines of the GP2X to the adapter plug of the BoB. (Both available on the BoB.) The easiest way to do this is by making a wire connection on the BoB from the left side of C43 (left side when the text C43 is in a normal readable orientation) to J2 (use the solder connection just above the text J2).

[Edit 11/06/2006, added pictures.]
Here's a picture.

And one to prove that it actually works.

What you have basically done is connected the power out of the GP2X to the adapter in of the BoB. This does have some consequences. READ ON!
All power drawn by the BoB now passes though the DC/DC converter of the GP2X. I have no idea how much current it can handle (the replacement mentioned here can handle 1A, but there's no info on the original) so be carefully when connecting USB peripherals.
Another issue is that the adapter plug of the BoB is now directly connected to the internal power supply of the GP2X. Thus supplying power to this plug equals supplying power to the internal circuitry of the GP2X without the safety of the DC/DC converter which normally regulates the power of your batteries / adapter. This is not so bad (I think, see questions) as long as your adapter supplies exactly 3.0 ~ 3.3 V. If you have a elcheapo adapter you are very likely to fry your GP2X when using this mod by aplying power to the BoB.
Last issue (I can think of right now) is that this mod would not be such a good idea when using a MK2 GP2X. Those units apparently supply 5V on pins 20 & 21. That would be quite a burden for the voltage regulator on the BoB (U11).

Alternative
An alternative would be to connect the 3.3V out of the BoB's voltage regulator (U11) to pin 20/21 of the BoB, and let the BoB power the GP2X. No idea how much current this regulator can handle though (see questions).
Or you can make a simple cable which lets you connect one adapter to both the GP2X and the BoB :p

Questions
-Most important question; How can the (unmodified) BoB be powering the GP2X, and how can the GP2X be powering the BoB. According to the wiki pin 20 & 21 are the Vcc lines, however these appear to be unused on the BoB. (They are connected to ground though capacitors C15 & C43).
-What's the function of pin 19? (If it is nRESET, is it incoming or outgoing as seen from the GP2X. Why don't I see it triggering?)
-How much current can the voltage regulator of the GP2X (MK1) handle?
-Can the voltage regulator be damaged when applying 3.0V ~ 3.3V on it's output pin while not supplying any power to it's input pin? (This is what happens when you use pin 20 / 21 on the EXT connector to power the GP2X.)
-How much current can the voltage regulator of the BoB supply (3.3V)?
-What's the point of connecting pin 20 & 21 of the EXT connector to ground via 2 capacitors on the BoB?
 
Something else to add to your list is that the bob doesn't actually need to be powered - all it needs is something shoving in the power socket (connect your adapter to the bob but don't plug into the mains to see this marvel of korean engineering in action).
 
Something else to add to your list is that the bob doesn't actually need to be powered - all it needs is something shoving in the power socket (connect your adapter to the bob but don't plug into the mains to see this marvel of korean engineering in action).

What?
 
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LOL. Shikaku, plug a power cord in, but you don't need to plug it into the actual outlet, and it works lol.
 
Something else to add to your list is that the bob doesn't actually need to be powered - all it needs is something shoving in the power socket (connect your adapter to the bob but don't plug into the mains to see this marvel of korean engineering in action).

Lol. Have you ever opened the cable that comes with the BoB. That's some handywork too ;)
 
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