Installing a serial interface to Bubba

A collection of tips on howto tweak your Bubba.
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johannes
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Installing a serial interface to Bubba

Post by johannes » 21 Mar 2007, 19:22

A few users wondered how to install an RS232 port to Bubba, enabling a direct shell access. This could come in handy if you messed up your network settings and need to restore, or probably for a lot of other good reasons I can't think of right now. :)

This is just a brief guide requireing some basic hardware knowledge. Let me know if anything is missing or need to be clarified.

*** NOTE ***
This requires you opening your Bubba and soldering wires to surface mount pads. You do risk destroying the hardware if not done carefully! This may void your warranty!

*** NOTE 2 ***
If you read note one and still want to proceed, be sure that you work in an ESD safe environment. This is something home users often neglect, something that very well may cause strange and inexplainable errors. A good place to do the dissasembly and soldering is actually on your kitchen sink. Make sure to touch the metal surface before opening Bubba.

Ok, action:

The Bubba internal serial port is a "TTL level" port (3.3V level), and will not work directly towards your PC without a 3V TTL - RS232 converter. You can either build something yourself (i.e. using something like the Maxim MAX3232 IC). Make sure to select one working with 3.3V, since some of them only work with 5V power supply.
The other (easier) option is to buy a ready-made converter board. A quick google search:
ET-MINI_RS232_3V.jpg
ET-MINI_RS232_3V.jpg (86.39 KiB) Viewed 12947 times
http://www.futurlec.com/Mini_RS232_TTL_3V.shtml

I also found one that looks nice at ebay:
:?
ebay.jpg
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http://cgi.ebay.co.uk/RS232-to-3-3-Volt ... dZViewItem
EDIT: A bit expensive though.

(This one needs 5-20V power supply, this is available on the board at the disk connector).

Note that I haven't ordered from any of those, and can't make any promises on their behalf.

Anyone know of other vendors?


So, do like this:

1) Remove the four hex screws on the rear panel.
2) Remove the rear panel, and gently slide the board (and disk) out of the case. If it's tight, loosen the four screws at the front as well. It is safe to pull at the USB connectors.
3) Now the board is exposed. The connector pads are located near the side of the board:
board.jpg
board.jpg (134.78 KiB) Viewed 12947 times
EDIT: (The image is for Bubba rev B board. The same things will work at the rev A board, but some details in the image may differ. For example, the resistor R79 next to the connector (J2) is only present in the rev B board. )

4) The signals:
signals.jpg
signals.jpg (71.64 KiB) Viewed 12947 times
Solder wires directly to the pads on the board, or, use a connector in between (the Harwin M50-3150522/M50-3500542 will fit, available from Farnell, art. no: 3078190 and 1022305). Be careful when soldering, if you heat up the pads too much, they may release from the board. Connect RX to the adapters TX (Tx from the PC to Rx on Bubba), and vice versa.

5) Connect the serial cable to your PC, and start a terminal program (such as windows HyperTerminal). Set your COM port to 115200 bps, 8,0,1. No hardware handshake.

6) Start your Bubba. The Linux boot log should appear in Hyperterminal. When booted, you'll get a login prompt. Just login as root (password is excito if you haven't changed it), and you're done!

Other useful links:
http://www.interfacebus.com/RS232_Pinout.html
http://www.farnell.com/

Please let me know if any information is missing, or if you have ideas on how to make this easier.

Good luck!
Last edited by carl on 05 Jul 2009, 09:57, edited 4 times in total.
Reason: fixing attachements
/Johannes (Excito co-founder a long time ago, but now I'm just Johannes)

John W
Posts: 62
Joined: 17 Jan 2007, 11:47

Post by John W » 21 Mar 2007, 20:13

Woho! Nice! :D

msx
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Location: Venice
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Post by msx » 22 Mar 2007, 04:38

Cool! :P
About other uses: what about connecting a motor driver, some motors and wheels from lynxmotion and have the first mobile bubba? :mrgreen:

oJsan
Posts: 3
Joined: 21 Sep 2007, 17:19

Post by oJsan » 21 Sep 2007, 17:56

Which are the other pins of the J2 header? I need to get hold of the DTR or RTS pin for a hack I hope will be useful for bubba users. But I believe the pinout of J2 depends on which UART of the ARM that has been used... some UARTs are missing som control pins...
Or is there any way to control a GPIO pin, like the one that controls the yellow LED?

Another solutions of how to install a serial interface to Bubba:
TTL-232R-3V3 from FTDI
This 3.3V serial to USB converter can be used to connect (almost) gluelessly between the J2 header of Bubba and a PC (even a PC without serial port, good for new laptops).
Just connect (solder) pins RX, TX and GND from J2 to corresponding pins of USB converter (actually, I haven't tried this but I'm pretty sure it'll work).
For Swedish Bubba hackers, check out Lawicel


(And NO, I can't use that USB-adapter to get a RTS-pin, :cry: I need to control it directly from the kernel)

johannes
Posts: 1470
Joined: 31 Dec 2006, 07:12
Location: Sweden
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Post by johannes » 22 Sep 2007, 12:28

oJsan,

J2 only has TX, RX, GND and +3.3V. RX and TX are connected to DRXD/DTXD on the arm chip, and this uart does not support modem signals. However, since we are using the PQFP package, all pins are available. Just check the Atmel AT91RM9200 data sheet to find our what pins you need to access. If you like, we can double check that we don't use those for anything else.

Controlling GPIO pins is easier, we have a few easilly accessible. The jumpers J5, J6, J7 and J8 directly connect to PB0, 1, 2 and 3 respectively. So, this is just a matter of of software. And of course, the LED is also GPIO controlled if you like to connect to that. Check this for a very easy way to control it.
/Johannes (Excito co-founder a long time ago, but now I'm just Johannes)

mike_nl
Posts: 49
Joined: 03 Jul 2009, 13:56

Re: Installing a serial interface to Bubba

Post by mike_nl » 05 Jul 2009, 04:48

@johannes:

i have seen in high detail the bubba 2 print. I have aown one (second hand).
He was not operational because a error in the power supply on the print.
But now it is fixed and he is running wel with V1.2.

1st. Bubba is a very great job from ecito.

2nd. It is possible that ecito will sold the peaces for serial add-on?
I mean not the hradware from the links. I mean the on print hardware.

It will be great. Ok no all have the know how to solder the SMD peaces.
But i think it is an idea.

mike_nl
Posts: 49
Joined: 03 Jul 2009, 13:56

Re: Installing a serial interface to Bubba

Post by mike_nl » 05 Jul 2009, 04:49

@johannes:

The photos from your 1st post... i can't see them anymore.
Can you fix it please.....

johannes
Posts: 1470
Joined: 31 Dec 2006, 07:12
Location: Sweden
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Re: Installing a serial interface to Bubba

Post by johannes » 05 Jul 2009, 09:58

Ok, fixed. Thanks for notifying, they got lost in a server move.
/Johannes (Excito co-founder a long time ago, but now I'm just Johannes)

carl
Posts: 474
Joined: 07 May 2008, 04:41

Re: Installing a serial interface to Bubba

Post by carl » 05 Jul 2009, 09:59

mike_nl wrote:@johannes:

The photos from your 1st post... i can't see them anymore.
Can you fix it please.....
I've readded the photos.

/Carl
/Carl Fürstenberg, Excito Software Developer
http://www.excito.com
support@excito.com

mike_nl
Posts: 49
Joined: 03 Jul 2009, 13:56

Re: Installing a serial interface to Bubba

Post by mike_nl » 07 Jul 2009, 04:50

@johannes & carl: Thanks for the fast response

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