UNO Q Serial Monitor, strange output

legoexpert2011 · February 5, 2026, 1:14pm

Experienced strange output in a complex motor controller sketch. So I wrote the following sketch to see what happens. Same garbled output.

#include "Arduino_RouterBridge.h"
int a = 0;
int b = 1;

void setup() {
  // put your setup code here, to run once:
  Monitor.begin();
}

void loop() {
  // put your main code here, to run repeatedly:
  Monitor.print("a = ");
  Monitor.println(a);
  Monitor.print("b = ");
  Monitor.println(b);  
  Monitor.print("a + b = ");
  Monitor.println(a+b);  
  a += 1;
  b += 1;
  delay(1000);
}

Screenshot Output in AppLab:

Screenshot Output in Arduino IDE:

Any idea, what's wrong

extender777 · February 5, 2026, 1:43pm

If you upload your sketch by Arduino IDE, output will be perfect

legoexpert2011 · February 5, 2026, 4:52pm

Unfortunately not, see screenshot above. Did you use Serial.println()?

GolamMostafa · February 5, 2026, 4:58pm

Why not Bridge.begin(); code?

Message/data from MCU goes to MPU through router bridge and then goes to Console>>python over the USB-C/USB-A connector.

legoexpert2011 · February 5, 2026, 5:28pm

I wanted to port a more complex sketch for motor controller from Uno to Uno Q.
This is only a test for calculations and output in the Serial Monitor.
Bridge.begin() alone did not change the situation with wrong end of line commands.
I will try data relay to Python and output in the shell later.

legoexpert2011 · February 5, 2026, 5:29pm

And I will try SBC mode.

GolamMostafa · February 5, 2026, 5:30pm

Follow SSS (start with Small Step) Strategy to see success!

ptillisch · February 5, 2026, 6:02pm

Hi @legoexpert2011. I think you are encountering this bug:

github.com/arduino-libraries/Arduino_RouterBridge

Output sent via `Monitor` object arrives out of order and corrupted

opened 10:25AM - 29 Jan 26 UTC

per1234

bug

### Describe the problem When a sketch transmits data via the `Monitor` object,… the messages arrive out of order and with incorrectly placed line breaks. ### To reproduce 1. Create the following sketch: ```cpp #include <Arduino_RouterBridge.h> void setup() { Monitor.begin(); } void loop() { Monitor.print("Reading 1: "); Monitor.println(1234); Monitor.print("Reading 2: "); Monitor.println(4567); delay(500); } ``` 1. Upload the sketch to an UNO Q board. 1. Open Serial Monitor. 🐛 The output from the sketch is not as expected: ```text Reading 1: 1234Reading 2: 4567 1234Reading 2: 4567 Reading 1: Reading 2: 4567Reading 1: 1234 Reading 2: 4567Reading 1: 1234 Reading 2: 45671234Reading 1: Reading 2: 4567 1234Reading 1: 1234Reading 2: Reading 1: 4567 Reading 1: 1234Reading 2: 4567 Reading 2: 4567Reading 1: 1234 Reading 1: 1234Reading 2: 4567 [...] ``` ### Expected behavior Output is received in order: ```text Reading 1: 1234 Reading 2: 4567 Reading 1: 1234 Reading 2: 4567 Reading 1: 1234 Reading 2: 4567 Reading 1: 1234 Reading 2: 4567 [...] ``` ### Arduino_RouterBridge version 0.3.0 ### Additional context We are seeing a spike of reports over the course of last few days. This seems to correlate with recent releases - "**Arduino UNO Q Board**" platform (`arduino:zephyr`) version 0.53.0 - Arduino App Bricks version 0.6.4 --- Originally reported at: https://forum.arduino.cc/t/why-an-update-messed-up-monitor-print/1427515 Note this: > I had my first simple sketch working then updated with a new patch for the MCU. Now the print formatting using Monitor is all over the place #### Additional reports - https://forum.arduino.cc/t/zephyr-wish-there-was-standard-way-to-speed-up-spi-operations/1426772/3 - https://forum.arduino.cc/t/arduino-uno-q-serial-monitor-broken/1427596 - They reported the following result from rolling back their `arduino:zephyr` installation to 0.52.0: > Working fine in Arduino App Lab - https://forum.arduino.cc/t/uno-q-monitor-garbled/1427874 > I uploaded extensive code, monitor worked GREAT. Flawless!! > Then I downloaded app lab, set up the linux side. > No apps are running. Yet, monitor is now completely garbled - https://github.com/arduino/ArduinoCore-zephyr/issues/322#issuecomment-3816480239 - https://forum.arduino.cc/t/stable-multiprocessing-readme/1427828/53

The developers are working on a fix:

github.com/arduino/arduino-router

fix: messages for the same target should be serialised (#27)

main ← serialize-handler-per-name

opened 03:22PM - 03 Feb 26 UTC

lucarin91

+107 -58

### Motivation We were exploiting too much parallelism; every RPC command was… concurrently executed, which led to out of order message for the same rpc call. Instead, we should serialize all the requests for the same rpc call. Concurrent requests by multiple parties will not guarantee an ordering, but at least all the requests from the same party will be locally ordered. ### Change description The proposed implementation uses a fixed number of concurrent worker and the requests will be distributed enforcing that the same RPC request is always sent to the same worker. The change also permits customizing the distribution by a key, that allow to handler tcp request for different sockets in parallel. ### Additional Notes - https://github.com/arduino-libraries/Arduino_RouterBridge/issues/52 ### Reviewer checklist - [ ] PR addresses a single concern. - [ ] PR title and description are properly filled. - [ ] Changes will be merged in `main`. - [ ] Changes are covered by tests. - [ ] Logging is meaningful in case of troubleshooting.

If you have a GitHub account, you can subscribe to that thread to get notifications of any new developments related to this subject:

legoexpert2011 · February 6, 2026, 7:26am

Thanks, I subscribed

thweight · February 7, 2026, 11:45pm

I also had lots of issues with printing out results. Here is what worked for me:

void setup() {
  Monitor.begin();
  delay(1000);

}

Give Monitor a chance to get its act together.

Get rid of the println’s since they don’t appear to work.

Use this instead:

    Monitor.print("******************\n");
    Monitor.flush();

Get rid of all ambiguity to avoid shuffling outputs as follows: Compose your string, then print it out.

    String tm_out = "Elapsed time = " + tm_elt + "\n end loop\n";
    Monitor.print(tm_out);

instead of something like:

Monitor.print("Elapsed time = ")
Monitor.println(tm_elt)
Monitor.println(" end loop")

Good luck.

legoexpert2011 · February 8, 2026, 10:31am

Thanks for your support.
Unfortunately, the line feed with "\n" did not work. See photo

And here the code snippet:

  printout = "Code = " + String(code) + "\n";
  Monitor.print(printout);
  delay(500);
  Monitor.flush();
  int forward = int(code/1000);
  printout = "forward = " + String(forward) + "\n";
  Monitor.print(printout);
  delay(500);
  Monitor.flush();
  int curve = int((code-1000*forward)/10);
  printout = "curve = " + String(curve) + "\n";
  Monitor.print(printout);
  delay(500);
  Monitor.flush();
  int button =  int((code-1000*forward) - 10* curve);
  printout = "button = " + String(button) + "\n";
  Monitor.print(printout);
  delay(500);
  Monitor.flush();

The good thing is: all this is preliminary code. Overall objective is a remote control of a robot car, where a 5-digit-code must be split into 3 components for "forward", "curve" and "button". I could see that this works properly.

Thanks again.

GolamMostafa · February 8, 2026, 10:50am

The C-code for Linefeed/Newline character is '\n' and NOT "\n".

legoexpert2011 · February 8, 2026, 11:58am

Does not make a difference. Neither as part of the string concatenation nor as stand-alone print statement.
Conclusion: FIFO and line feed are not yet working properly.

qubits-us · February 8, 2026, 7:08pm

curious,
what happens if you replace all the '\n' with '\r' ??
Monitor.print("loop\r");// seems to work..
~q

legoexpert2011 · February 8, 2026, 8:03pm

Much better. Thank you.
However, FIFO still has some hick-ups (random). See ScreenShot.

"Code - forward - curve - button" is one block per iteration.

qubits-us · February 8, 2026, 8:04pm

watch out for any println's..
seems like \n blows it up??
~q

legoexpert2011 · February 8, 2026, 9:18pm

void Code(int code)   {
  printout = "Code = " + String(code) + '\r';
  Monitor.print(printout);
  delay(300);
  int forward = int(code/1000);
  printout = "forward = " + String(forward) + '\r';
  Monitor.print(printout);
  delay(300);
  int curve = int((code-1000*forward)/10);
  printout = "curve = " + String(curve) + '\r';
  Monitor.print(printout);
  delay(300);
  int button =  int((code-1000*forward) - 10* curve);
  printout = "button = " + String(button) + '\r';
  Monitor.print(printout);
  delay(300);
  printout = "\r";
  Monitor.print(printout);
  delay(300);
}

Now, this part is excellent. Printout as expected, Code seperated in its components.
No println(), an empty line produced with
printout = "\r";
Monitor.print(printout);

But here, the code stems from the Python program through the Bridge. The overall objective is a remote control with HC-12 (433MHz). That's another issue.

Thanks

qubits-us · February 8, 2026, 10:01pm

sorry can't help with the python..
but i would try ending the lines with carriage returns, like we are printing..
i'm sure it's being worked on..
~q

qubits-us · February 11, 2026, 1:16am

If anyone is curious..
I've been looking real hard at this for few days now..
println calls monitor write twice not necessarily a newline issue..
1st call we get the string..
the next call has 2 chars, i haven't bothered to check i'm sure it's just a newline and carriage return..
i think i'm starting to get my bridge to a stable state..
i would like to override println and see if I can get that to just one call to write??
my write is tight, blocking with the mutex, current code is loose..
need more testing time myself..
my test sketch..

#include <Arduino_RouterBridge.h>

void setup() {
  Serial.begin(115200);
  pinMode(LED_BUILTIN, OUTPUT);
  Monitor.begin();
}

void loop() {
  static unsigned long count = 1;
  Monitor.println("Start of loop..");
  Monitor.print("Loop:"); Monitor.println(count);
  count++;
  digitalWrite(LED_BUILTIN, LOW);
  delay(1000);
  digitalWrite(LED_BUILTIN, HIGH);
  delay(1000);
  Monitor.println("End of loop");
}

results thus far..
orig bridge on left, modified on right..

sorry.. ~q

qubits-us · February 11, 2026, 1:46pm

I've determined it's probably somewhere else..
Quite easy to see add a k_msleep(10) to the top of monitor write..
After taking out my debug prints, it went sideways..
If I insert a 10ms delay, added it to the end before releasing mutex then it all got better..
Was my first test to try this morning, installed orig code and added the delay..
added it to the top..
cleaned it right up..
println does try to clobber with two quick punches..
the other end not fast enough??
or we need a sequence added..
just another episode of as the code compiles..
src.zip (11.3 KB)

sorry.. ~q

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UNO Q Serial Monitor, strange output

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