3/28/2021 0 Comments Logic Level Shifter Circuit
When the adapter TxD is at a logic ZERO level, there will be no current flowing through diodes D2 and D3, and the kindle will see a logic ZERO.It has been reported to work if your Kindle is stuck at the startup screen with no progress bar, and it also works if you kindle is stuck at the dreaded Repair Needed screen (like mine was).
Logic Level Shifter Circuit Serial Port ConnectionNo serial port connection is required, so no need to open up the Kindle back cover.EDIT: This schematic is used for Kindle Touch serial recovery (debricking) as described in this thread: I would recommend just getting a USB to 1.8v TTL serial adapter, but for those who requested a schematic when I described this circuit in various posts and multiple times on the IRC channel, here is the level shifter circuit that I used with my 3.3v USB serial adapter to recover my bricked Kindle Touch: You can harvest resistors and diodes from discarded circuit boards. To use salvaged surface mount components, I recommend soldering small wires to them first. You can also peel small wires from old computer ribbon cables. I peeled a strip of 3-wires from an old IDE cable, which soldered nicely to my kindle after stripping and solder-tinning both ends of the wires. EDIT: You can substitute a common red LED in place of the two diodes in the kindle RxD level shifter circuit. A red LED has 2.2v across it while conducting current, which although a bit higher than specified input voltage, should work fine with the kindle RxD. ![]() Although I did use a red LED in a level shifter circuit for a cellphone USB adapter cable when I debricked my OLPC (One Laptop Per Child aka XO computer), I did not test an LED in this circuit on my kindle touch. EDIT: You can also harvest silicon diodes from the electronic ballast circuit in a Compact Flourescent Lamp (CFL, the twisty kind). If you use this, you agree that you will use it at your own risk. And please be careful to not poke your eye out with that hot soldering iron. All 5v and 3.3v TTL devices must output at least 2v for a logic ONE under normal operating loads, and must accept any voltage from 2v to 5v as a logic ONE. All 5v and 3.3v TTL must accept any input voltage below 0.8v as a logic zero, but should output 0.5v for logic ZERO (to allow for some voltage drop due to long narrow conductive traces on a circuit board). TTL must accept any input voltage above 0.65v as a logic ONE, and any input voltage below 0.35v as a logic ZERO. Voltage levels between the logic ONE low voltage and logic ZERO high voltage specifications are undefined and cause TTL circuits to operate in the linear range where they may draw excessive current, and must be avoided except in special (hack) circuits specifically designed to use their analog properties. Read more about TTL voltage levels and level shifting here: and here: Kindle TxD level shifter circuit description: When the kindle outputs a TxD logic ZERO, the level shifter uses diode D1 to let the kindle pull the adapter RxD pin down to 0.7v (the voltage drop across one silicon diode while conducting current through it). When the kindle outputs a TxD logic ONE, diode D1 blocks current flow, and resistor R1 pulls the adapter RxD pin up to its logic ONE level. Anything from 2v to 5v should work fine for the adapter RxD circuit supply voltage. For some USB serial adapters, you may not need resistor R1 or the supply voltage (due to an internal pull-up resistor), but it will not hurt to leave them in the circuit. USB Serial adapter modifications (if needed): If the serial adapter contains an LED that lights to show data on its RxD line, that diode might supply too much current for the kindle to pull it down to a logic one. You can measure this with an oscilloscope as the lowest voltage level on the pulsing data line while serial traffic is flowing across it. If the PC connected to the adapter USB port does not see data, you might have to remove that RxD LED (like I did on mine) to get it to work. Kindle RxD level shifter circuit description: The kindle RxD level shifter uses diodes D2 and D3 to limit the adapter TxD output to 1.4v (the voltage drop across two series-connected silicon diodes while conducting current through them). Resistor R2 limits the current flowing though the diodes to a safe value that will not overload the adapter TxD output.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |