Decoding a UART signal with gpio pin

Using Arduino Project Guidance
1

Hi there, i am working on a signal that is similar to a UART signal. But if I connect it to the serial port (rx) to decode, it doesn't so any result. So I tried changing the baud rate. I did not get any results.
So I decided to plug that signal to gpio pin and decode it as 1's and 0's.
But I am not sure how to code for it . Can anyone help me out giving some ideas and a sample example how can I do it

Thanks in advance :cowboy_hat_face::cowboy_hat_face:

2

What is the source of that signal? Do you have an oscilloscope or logic analyzer?

A simple Serial.print(digitalRead() might be a start.

void loop()
{
  Serial.print(millis());
  Serial.println(digitalRead(yourPin));
}

might be a start. Use a 3rd party terminal program that can log to file. Use the highest possible baudrate for communication with the PC.

Below a more extensive example; it uses state change detection. We assume that the signal is high when there is no transmission (as a UART would be). The code checks if the signal level changes and if that happens it prints a duration and the level; this way you might eventually be able to determine a baudrate. The shortest time will (more than likely) be a bit time.

uint8_t uartBit;      // received
uint8_t prevBit = 1;  // previously received
uint32_t lastTime;    // remember when state change was detected

const uint8_t somePin = 5;  // gpio pin

void setup()
{
  Serial.begin(1000000);  // use the highest baudrate supported by 3rd party terminal program
}

void loop()
{
  uartBit = digitalRead(somePin);
  if(uartBit != prevBit)
  {
    Serial.print(millis() - lastTime);
    Serial.print(" ");
    Serial.println(uartBit);
    prevBit = uartBit;
    lastTime = millis();
  }
}

Code not tested

Signal example

I   S   1   1       3         2     1   P   I
--+   +---+   +---+---+---+       +---+---+-----------
  |   |   |   |           |       |
  +---+   +---+           +---+---+

I = idle
S = start bit
P = stop bit
N = number of unchanged bits

You can e.g. get something like

xxx 1   idle time
100 0
100 1
100 0
300 1
200 1
        nothing here as code waits for a state change
1 Like
3

Please provide more details of that:

  • How did you determine that it's "similar" to a standard "UART signal"?
  • In what way(s) is it the same as a standard "UART signal"?
  • In what way(s) does it differ from a standard "UART signal"?
  • Do you have any documentation?
  • Do you know the baud rate?

As @sterretje suggests, the first thing to try would be a standard serial terminal - far easier to experiment with different configurations than having to write, rebuild, and download code to an Arduino each time! A logic analyser and/or oscilloscope would be the tools to use next if you can't get any joy with a standard serial terminal

1 Like
4

Where does this signal come from? Maybe that it is simply inverted? Check what is the idle state of the signal.

1 Like
5

Without knowing what clock signal is being used to generate your mystery signal, you CANNOT DECODE IT!

6

IMG_20231014_181747773~2
IMG_20231014_181747773~23437×944 386 KB

7

It is the indoor to outdoor communication signal of inverter air conditioning

8

Ah ha! So you do have a clocking signal that you have created to produce that documentation. Now you can figure the Baud rate of the signal.

9

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