Both parts are used as a USB-UART converter: the part in the left is a CH340G, and the part in the right is a socket for a FTDI.
Connnection with the FTDI is OK, I can connect to the uC, upload scripts... Everything fine. But with the CH340G, I can't recieve nor send anything.
I know that the USB connection is OK, since my PC detects whenever I plug the USB wire. The port appears in the IDE, I can open the serial monitor... When I write something to the port, the TX LED blinks for a short time. I can also see the RX LED blinking when the uC is sending, but nothing appears on the Serial Monitor.
Use any short wave receiver that will listen to 12 mHz. Put the antenna close to the crystal and tune the receiver. If the oscillator is working you will hear it!
Sorry for the wrong explanation. The FTDI can be plugged and unplugged very eqsy, since it is connected to the board with some headers. When I try to connect to the uC using the CH340G, the FTDI is unplugged.
The worst thing I can imagine happening connecting both FTDI and CH340G is that the Tx pin gets damaged (since you are connecting two outputs together), but it seems ok since the LES blinks when sending data using the CH340G. The Rx pin should be ok
Post complete schematic that shows which MCU and how it is being connected with the CH340G. Note that X4, as also mentioned in post #2@Paul_KD7HB , must be a 12 MHz crystal.
You may check your scematic with the following working schematic:
Uploading the only part where RX and TX interfear. I didn't post it since I thought that the RX and TX signals arrived fine in the other picture, since it is working with the FTDI.
As long as I know, the xtal is a 12 MHz crystal. Am I wrong?
Changing C8 to 100nF did not solve the problem. It keeps with the same.
DId not really get the formula you sent:
CL = (C1*C2)/(C1+C2) + 5pF
Assuming C1 = C2, does this mean CL is always 5pF?
Anyway, do you think that the capacitors can be the problem? I used to run some ATMEGA at 16MHz without capacitors on its crystal... Despite not being optimal, it did something. Here it does nothing.
However, you are right it isn't your problem.
Is this being used to program some microcontroller or just as an USB to serial adaptor.
EDIT: fixed equation
I would like to use it as a USB-UART converter. Since it is an ESP32, it woul also be used to upload code into the uC, but if serial communication works, that should not be a problem.
I was again suspecting of the xtal value. I once had a MCP2515 (SPI - CAN controller) that was running with a xtal of 8MHz or 16MHz. If the xtal placed was the 8MHz, and you configurated the chip to run with a xtal of 16MHz, everything did work fine, except the CAN seemed to be working twice the baud rate it was actually going. Just to put an example, with that configuration, you needed to configurate the chip at 1MBits/sec, in order to read data being sent at 500kBits/sec.
Is it possible that something similar is happening here? Like for example, if the xtal is oscillating at a strange frequency, I would have to change the baud rate I am reading in order to read at 115200. I don't know if it has any sense...
That's why my main point was to check the xtal oscillating frequency.
If the xtal is off more than +/-0.25% than the USB probably would not work.
However I guess it could throw off the baud rate.
Have you tried a slower baud rate.
