Thread: Help with unbricking kindle via serial port
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Old 03-10-2011, 07:51 AM   #13
yifanlu
Kindle Dissector
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Posts: 662
Karma: 475607
Join Date: Jul 2010
Device: Amazon Kindle 3
Quote:
Originally Posted by axsdenied View Post
I have been following these forums for a while so I might as well post something useful in my 1st post :-)
For the record, I have built similar converters for various devices in the past (not for the Kindle but there are all more-or-less the same ).

First of all the important stuff to prevent you from killing your Kindle :
  • You said that you measured VCC=2.8V on the Kindle. This would imply that you need 2.8V instead of 1.8V on the RX and TX lines. Everybody else is talking about 1.8V... are you sure you have 2.8V?
    What is the voltage on the RX and TX lines (relative to GND)?
    Which Kindle model?
  • If you connect the VCC lines between the Kindle and the serial converter, make sure you don't connect 1.8V from the Kindle to 5V on the FTDI chip. This will definitely kill the Kindle. Only connect the power lines if they have the same voltage (or use resistors - not in this case).

So, assuming that you need 1.8V:
  • You need an USB to RS232 converter that gives serial lines at 1.8V (for example they come in 1.8V, 2.8V, 3.3V, 5V). If you use the wrong voltage, you may kill your Kindle.
  • If you can find one in the shops, great. They will most likely use an FTDI chip. You don't need the power line from the Kindle (VCC) to the FTDI chip. The FTDI module (USB to serial converter) will draw power from the USB port while Kindle will power itself from its battery.
    You need only RX, TX and GND. Again, make sure it is the 1.8V version.
  • If you are building one using the mentioned FTDI chip (FT232R series for example) make sure that you connect the 1.8V from the Kindle (VCC) to the VCCIO line on the FTDI chip - this will give you 1.8V RS232.
  • You have to cross over the RX and TX lines between Kindle and FTDI chip, i.e. RX <-> TX and TX <-> RX.

Also:
  • Measure all voltages before you connect things together.
  • To test your old DOA module or before you connect the self-built module to the Kindle, connect the RX and TX lines together. This will echo anything you send from a terminal program (I use wxterm on the Windows). If you get nothing back, the module is not working.
Thanks for the info. I was wrong about the 2.8V. I don't know how I got that, but measuring the port right when it's turning on gives me 1.8V.
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