In order to get
USB OTG support on my Kindle, I had the debug the kernel and attach a serial circuit.
I used
this Sparkfun breakout based on the excellent FT232RL chip.
What is great about this chip is that it has a VCIO pin on which you can supply any voltage you need. I combined this with a simple voltage divider for 1.65v.
This works great for reading kernel output, but sending data only works when the Kindle is plugged in to USB.
I'm not sure if this is related to speed or voltage. I admit my voltage/current might be on the low side with two 10k resistors.
When sending data while not on USB, I observe the following transmission:
Code:
pressed: g(1100111)
received: G(1000111)/g(1100111)
pressed: o(1101111)
received: o(1101111)/O(1001111)
pressed: s(1110011)
received: o(1110011)/c(1100011)
pressed: t(1110100)
received: t(1110100)/p(1110000)
pressed: p(1110000)
received: p(1110000)/`(1100000)
A couple of other characters degrade to `, while a newline seems to degrade to a tab or carriage return and backspace has no visible effect.
Again, when the Kindle is connected to USB it works fine.
Blogpost:
http://pepijndevos.nl/2012/10/26/spa...to-serial.html