How to use Wemos D1 as a USB-to-Serial converter?

can someone explain a bit better how to use this TTL/uart function on wemos d1 r2?
i have an external device which should basically send data over 3,3volts uart port, but i have no idea how should i connect things...

so the device has 5v input!, Rx, Tx and Ground pins
which pins should i connect them on Wemos D1?

Does the device Rx go to Wemos Rx pin or Wemos Tx pin etc? like does it have to be like a crossover cable or just a normal straight cable? (aka Rx to Rx and Tx to Tx?) or why does someone cross them over then if they need to be 1:1?

if i could get this X-X part sorted out, then i can probably find the X pins on the Wemos myself(probably the only Rx and Tx pins on the IOL1 jumper?), but the thing is just so confusing when first starting up with things....

And the data transfer over these Rx and Tx pins work at 3,3 volts then, even if the device itself needs 5volts to power itself up? Like the input and data stream operate at 2 different voltages?


You have two problems:

  • the USB to serial conversion
  • the signal voltage level

The first one is astonishing easy: remove the controller chip from the Uno board, and use the Tx pin for serial input (to TX), and the Rx pin for output (to RX). This way you only use the USB controller as an USB to serial converter, that's why the Rx/Tx pins swap their functionality. Obviously a dedicated USB to serial converter is a cheaper solution, which also should be configurable for 3.3V signal levels.

The "TTL/UART" suggests 5V signal level, so that you might connect both devices directly. Don't forget the Gnd line!
But if the board operates on 3.3V, it's safer to insert a resistor (10k?) or voltage divider into the Uno output (Rx) line, to reduce the output signal level. If the Tx level is not high enough for transmission to the PC, a level shifter (non-inverting amplifier) is required.

USB is serial, and what board are you working with? Title says Uno, post says Wemos/ESP8266.

sorry, the thread was started from another topics post(and i didnt realize that i should change the title...), but my board is Wemos D1 r2

so basically i should connect Reset and Ground together to get the Tristate/Uart mode and then connect the external device and D1 via Rx to Rx and Tx to Tx? and maybe try giving the sensor 3,3volts instead of 5V? (i now remembered that someone actually did this on the internets...)

or still device Rx to wemos Tx and device Tx to wemos Rx? (aka the first pins on the IOL jumper?)
i still dont get it why are these switched sometimes and sometimes not...

Usually Tx (transmitter output) connects to Rx (receiver input).

ok, but that is when the processor is doing stuff in the middle?
and when i remove the cpu(by connecting reset and ground on Wemos d1) i need to connect the pins with a new way, aka straight from Rx to Rx and Tx to Tx?:x

well, i now got another manual for the device and that one said that device Tx should go to reader Rx and device Rx to reader Tx....
but the question now is.... does the wemos d1 board actually allow to use those pins while the processor is in the middle or do i still need to ground it into the Uart mode and then still use the 'crossover cable' as a connection?:s
or if the wemos board allows to use the Rx+Tx pins in live mode, then i would need to use straight cable in the Uart mode?:s
altho i have a feeling that maybe i still need to use the 'crossover cable' in the Uart mode of the wemos board then?:x

This is not the forum about the Wemos.
You should ask your question there.

Please clarify your hardware configuration. Do you want to use the Uno board as USB to serial converter, or what else?

Please clarify your hardware configuration. Do you want to use the Uno board as USB to serial converter, or what else?

As I understand it, he has a Wemos D1 R2 not an Arduino Uno.

well yes, i have wemos d1 r2 board, but i found the previous topic via google, so i thought that i can ask here, especially when these boards had to be quite similar...

And is there any USB to serial issue?

yes. the issue is that i dont really know how to use the plain Uart mode of the board.... and how to connect the wires in those 2 different modes:

  1. do i need to connect device Rx to Wemos Tx and device Tx to Wemos Rx while the jumper cable is between Reset and Ground also(to put it into the plain Uart mode)?
  2. Do the Rx and Tx pins also work in normal Live mode somehow and then i would need to connect device Rx to Wemos Rx and device Tx to Wemos Tx? (i dont really need this function at the moment, but this would double-confirm which way i would need to connect the wires....)

See reply #4. “Usually” means “unless the labels have been reversed by the designer”.

well, dunno if anything is reversed or not, but now i can confirm that in the plain Uart mode(Rst bridge to Gnd), i had to connect Rx to Rx and Tx to Tx to get the stuff working....

and fortunately i probably did not burn anything down in the process, because it did not work with Rx to Tx etc at first...

Can I use fingerprint sensor with wemos d1r2.