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.
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This works great for reading kernel output, but sending data only works when the Kindle is plugged in to USB. :chinscratch:
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:
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
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. :chinscratch:
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)Again, when the Kindle is connected to USB it works fine.
Blogpost: http://pepijndevos.nl/2012/10/26/spa...to-serial.html