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Old 09-20-2012, 02:13 AM   #21
geekmaster
Всё гениальное просто.
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Quote:
Originally Posted by knc1 View Post
The photo shown on the page linked to showed one of those "general purpose" adapter boards, which from the silk screen markings looked to be a 5.0 / 3.3 volt board.

I requested the Make/Model of the board but am still waiting for that answer.
3.3 is not enough if it has an unbuffered LED lit by a logic zero on the kindle TxD. Both 3.3v and 5v TTL use the same logic zero/one switching zone, and the kindle cannot output below that with too high of an external pull-up resistor.

And 1.8v TTL uses lower voltage ranges for switching, so needs a logic zero on its RxD even closer to 0v. I made my k4 and k5 use "open collector" inputs with a series diode, so either side can pull it to GND, and both sides pull their end up to their preferred logic one. And I removed that pesky serial status LED on my 3.3v serial adapter that interfered with kindle TxD output.

It is easier to use a real 1.8v adapter, but they are hard to google because they come in a 1.8m standard length, which confuses the search results. Cheaper to hack a level converter (if needed) for a cheap 3.3v serial adapterusing the "super simple" serial level shifter I published...

But only testing will tell if you need it, and there is that "unreliable GND" issue on the serial connectors...
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