Arduino Serial read on monitor

Projects Programming
1

Hi

I would like to know if a Arduino Nano is able to read and display serial from a pc to the serial monitor.

I use a usb serial to TTL 5v logic programming cable to send the data.

RX and TX and GND is connected to the Arduino ,i also swapped the RX and TX pins but does not see any data on the serial monitor.

I can confirm the short data burst is present with a scope.

The Arduino is progammed with Blink.

I use 2 computers one to send the data to the Arduino and the other connected to the Arduino usb port.

My understanding is that only the usb chip transfers the data back to the pc .

What am I missing?

Thanks in advance. :confused:

2

You need to give a better description of what you want to achieve.

The only tip I can give now is that on the Nano, RX and TX are shared with the USB communication. You can look at SoftwareSerial or (the better) alternatives NeoSWSerial and AltSoftSerial if you need a second serial port functionality in the Nano's software.

3

Hi

Thanks,on the old Win98 or around there a program called Hypertermal could read serial data Ascii characters

and display the string.

I know there is a lot op programs that still does that but I was thinking that the Arduino monitor function could

also do that using the serial to usb chip on the pcb.

If I use 2 computers and 2 Aduino Nano's with the GND pin connected and the RX and TX pin swapped will I be

able to send (Ascii characters)from the one pc to the other pc using Arduino monitor on both sides?

4 
        +-----------+       +-----------+
        |           |       |           |
        |    N   TX |-------| RX  c     |
  USB --|    a   RX |-------| TX  o     |-- USB
        |    n      |       |     n     |
        |    o      |       |     v     |
        |           |       |           |
        +-----------+       +-----------+

Like this?

Should work (to my knowledge) if you keep the Nano permanently in reset.

The USBs go to the respective computers.

Note:
mistake in diagram, see reply #5

5

Yes spot on.

Why must the Nanos be kept in reset??

I will try with 2 Nanos tonight and see what happens.

6

First, there was a mistake in the drawing in reply #3. It should be TX to TX and RX to RX.

Explanation below

              Nano                       Conv
        +--------------+           +--------------+
        |              |           |              |
        |   +------+   |           |   +------+   |
  USB --|---| FTDI |   |           |   | FTDI |---|-- USB
        |   |      |   |           |   |      |   |
        |   | R  T |   |           |   | R  T |   |
        |   | x  x |   |           |   | x  x |   |
        |   +------+   |           |   +------+   |
        |     |  |     |        RX |     |  |     |
        |     |  +-----|----->-----|-----+  |     |
        |     |        |        TX |        |     |
        |     +--------|-----<-----|--------+     |
        |              |           |              |

This shows how the two TTL-to-USB chips (one in Nano, one in the converter) should be wired to be able to communicate. At the Nano side, I've left the actual pins out. I named the chips FTDI.
So the Tx of the one FTDI chip goes to the Rx of the other one and vice versa.

In below I've added the 328P in the Nano

              Nano                       Conv
        +--------------+           +--------------+
        |              |           |              |
        |   +------+   |           |   +------+   |
  USB --|---| FTDI |   |           |   | FTDI |---|-- USB
        |   |      |   |           |   |      |   |
        |   | R  T |   |           |   | R  T |   |
        |   | x  x |   |           |   | x  x |   |
        |   +------+   |           |   +------+   |
        |     |  |     | RX     RX |     |  |     |
        |     |  +--R--|----->-----|-----+  |     |
        |     |  |     | TX     TX |        |     |
        |     +-----R--|-----<-----|--------+     |
        |              |           |              |
        |     |  |     |           |              |
        |     |  |     |           |              |
        |     |  |     |           |              |
        |   +------+   |           |              |
        |   | T  R |   |           |              |
        |   | x  x |   |           |              |
        |   |      |   |           |              |
        |   | 328P |   |           |              |
        |   +------+   |           |              |
        |              |           |              |
        +--------------+           +--------------+

I've now also named the physical pins on the Nano.

As (hopefully) can be seen, the Tx of the 328P on the Nano goes to the Rx of the FTDI on the Nano. But that same Tx pin of the 328P is also the physical TX output pin of the Nano; same for the RX. So the Nano's TX pin needs to be connected to converters TX pin and the Nano's RX pin to the converters RX pin.

TX pins are outputs and one should never connect outputs together (unless they are open collector / open drain). The Nano has resistors for protection to prevent you from blowing the 328P's blowing up if you accidentaly connect the TX pins; indicated by R in above drawing.

====
So you have now two outputs driving against each other. If the 328P has its uart active, the 328P's Tx pin will be actively driven HIGH (serial idle state). If the converter's TX pin is now driven LOW, the FTDI on the nano will not see it because the 328P's Tx pin is HIGH.

If you keep the 328P on the Nano in reset, all 328P IO pins will be high impedance and the 328P will not have 'the power' to drive its Tx pin HIGH.

7

Thanks

I did not connect the RX line (only want to see the TX data) so the Arduino monitor did not work.

When I connect the RX line the Arduino monitor displays the data.

When the RX line is floating and not in the correct logic state the serial monitor does not read the data.

I can now read data send from one pc with a Kenwood program lead (TTL 5V) to a second pc using an Arduino and the serial monitor.