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CH340g TX doesn't work

PostPosted: Tue Jan 19, 2016 7:01 pm
by Magnetz
I have a ch340g USB serial adapter connected to the yellow test board (3xAA) via a 4 channel level converter.

I receive the boot message:

Ai-Thinker Technology Co.,Ltd
ready

But I can't transmit anything. The only way I can transmit is to connect a multimeter across tx and ground (or rx/ground on esp) then transmit, which works.

I have (usb/level converter)
RX->HV2
TX->HV1
VCC->HV
GND->GND

Then (level converter/esp test board)
LV1->TXD (it's actually RXD on the esp because the board is mislabelled)
LV2->RXD (txd)
GND->GND
LV->VCC

Does that all look OK?

Re: CH340g TX doesn't work

PostPosted: Wed Jan 20, 2016 5:33 am
by eduperez
Why don't you just use a 3.3v FTDI?

Re: CH340g TX doesn't work

PostPosted: Wed Jan 20, 2016 12:40 pm
by Magnetz
eduperez wrote:Why don't you just use a 3.3v FTDI?


The only usb adapter I have is a ch340g. It has a 3v/5v switch but it only switches the vcc line, logic levels are always 5v! :!:

Re: CH340g TX doesn't work

PostPosted: Wed Jan 20, 2016 12:59 pm
by DrG
Magnetz wrote:I have a ch340g USB serial adapter connected to the yellow test board (3xAA) via a 4 channel level converter.

I receive the boot message:

Ai-Thinker Technology Co.,Ltd
ready

But I can't transmit anything. The only way I can transmit is to connect a multimeter across tx and ground (or rx/ground on esp) then transmit, which works.

I have (usb/level converter)
RX->HV2
TX->HV1
VCC->HV
GND->GND

Then (level converter/esp test board)
LV1->TXD (it's actually RXD on the esp because the board is mislabelled)
LV2->RXD (txd)
GND->GND
LV->VCC

Does that all look OK?


I have some experience with that yellow board. Not sure if this will help, but here are my thoughts:

1. Make sure we are talking about the same pin connections on the board. The pic illustrates how I would do it, depending upon where I was connecting. Image

2. Verify that your level shifter is working properly. Sometimes they are not what they seem (look at the comments for the one advertised here http://www.banggood.com/Two-Channel-IIC-I2C-Logic-Level-Converter-Bi-Directional-Module-p-970227.html

3. Dump the batteries and use a known good supply that outputs at least 500mA - since there is a 3.3V regulator on board, I use a 5V 1 amp supply for testing. When it is working, you can go back to the batteries.

You are close, so let us know what the problem was.

Cheers,
DrG