MobileRead Forums - View Single Post - Kindle serial adapter level shifter circuit

noisymime · 01-12-2019, 10:16 PM

Resurrecting this thread just incase my experience helps anyone else.

I used the above circuit on a PW3 with a 3.3v serial adapter (Sparkfun FTDI Basic) and ran into issues with sending any data. Receiving from the kindle worked fine, but anytime I sent anything to the kindle it went through garbled. Tried with many different values of R2, but had the same issue.

I left the R1 and D1 part of the circuit as is, but removed R2, D2 and D3, replacing them with a simple voltage divider consisting of a 2k and 2k4 resistor to drop the 3.3v down to 1.8v. Obviously the values of these resistors would need to be different if using a 5v adapter. This all worked completely fine though and the commands were then successfully received by the PW3.

A big thanks to Geekmaster for the circuit diagram!

01-12-2019, 10:16 PM	#7
noisymime Junior Member Posts: 4 Karma: 10 Join Date: Jan 2019 Device: PW3	Resurrecting this thread just incase my experience helps anyone else. I used the above circuit on a PW3 with a 3.3v serial adapter (Sparkfun FTDI Basic) and ran into issues with sending any data. Receiving from the kindle worked fine, but anytime I sent anything to the kindle it went through garbled. Tried with many different values of R2, but had the same issue. I left the R1 and D1 part of the circuit as is, but removed R2, D2 and D3, replacing them with a simple voltage divider consisting of a 2k and 2k4 resistor to drop the 3.3v down to 1.8v. Obviously the values of these resistors would need to be different if using a 5v adapter. This all worked completely fine though and the commands were then successfully received by the PW3. A big thanks to Geekmaster for the circuit diagram!