Serial over TX pin Arduino UNO

I'm trying to get my UNO to output Serial.println commands over pin 1 (TX) to a USB-UART adapter on a windows machine that's running PuTTY in Serial mode. The reason for this is that my UNO's application runs smoothly when it's powered over USB and I'm using the IDE as my serial monitor, but when I switch from USB power to a wall-wart I get random issues where my UNO detects signals that aren't present. I'm trying to get serial out over pin 1 working so that I can debug what's going on while the UNO is pulled into a wall-wart.

Can anyone offer me any assistance? I've tried the Software Serial Library without much success..

Thanks!

I would focus on the power problem first. Can you measure the voltage on the Vin pin while being powered from an external source?

One generally shouldn't require software to determine if there is a power supply problem or not. Hardware troubleshooting should be your course of action in my opinion.

Lefty

I'll try to get my hands on a multimeter to measure it, in the mean-time I moved to a far less complex sketch to troubleshoot this issue.

void setup() {                
  Serial.begin(9600);
  pinMode(9, OUTPUT);     
}

void loop() {
  digitalWrite(9, HIGH);
  Serial.println("Hello World!");
  delay(1000);
  digitalWrite(9, LOW); 
  Serial.println("Goodbye World!");
  delay(1000);
}

When the UNO is powered over USB, I get the serial output in both the IDE serial monitor and in my PuTTY session on the other computer.

However I still run into the issue that when I plug in a wall-wart I don't receive the serial output on the PuTTY session anymore, but the LED does blink so I can verify that the program is running.

When the UNO is powered over USB, I get the serial output in both the IDE serial monitor and in my PuTTY session on the other computer

How is the arduino tx serial data (pin 1) getting to the ‘other computer running Putty’, a separate TTL serial USB cable or such?

Lefty

retrolefty:

When the UNO is powered over USB, I get the serial output in both the IDE serial monitor and in my PuTTY session on the other computer

How is the arduino tx serial data (pin 1) getting to the 'other computer running Putty', a separate TTL serial USB cable or such?

Lefty

Yes, I'm using a Silicon Labs cp2102 based usb to uart adapter.

I hooked up a 5mm blue LED to the VIN and to a GND on the UNO, when USB powered it lights up nice and bright, when on any of my AC Adapters, it doesn't light up at all.. I'm wondering if it will light up at the same time that the serial output works ;)

What is the voltage/current rating on the wall-wart - is it at least 7.5V DC (not AC) and a few hundred milliamp??

I hooked up a 5mm blue LED to the VIN and to a GND on the UNO

With a properly size series current limiting resistor I hope?

Lefty

CrossRoads: What is the voltage/current rating on the wall-wart - is it at least 7.5V DC (not AC) and a few hundred milliamp??

I've tried two 12V DC plugs, one operating at 500mA, the other at 300mA.

retrolefty:

I hooked up a 5mm blue LED to the VIN and to a GND on the UNO

With a properly size series current limiting resistor I hope?

Lefty

Nope I actually forgot, worked fine when I was powering over USB, but it blew it out when I tried one of my DC plugs :roll_eyes:

I'll never forget that again!

CodedChaos:

retrolefty:

I hooked up a 5mm blue LED to the VIN and to a GND on the UNO

With a properly size series current limiting resistor I hope?

Lefty

Nope I actually forgot, worked fine when I was powering over USB, but it blew it out when I tried one of my DC plugs :roll_eyes:

I'll never forget that again!

Actually it shouldn't light at all when just powered by the USB, however there does seem to be some +5vdc leakage current through the auto-voltage switching FET that was allowing the LED to light without damage. However when applying external power to the board with a LED without resistor you were effectivly short circuiting the external power module.

So I assume everything is working now as expected once the blue led was removed?

Lefty

retrolefty:

CodedChaos:

retrolefty:

I hooked up a 5mm blue LED to the VIN and to a GND on the UNO

With a properly size series current limiting resistor I hope?

Lefty

Nope I actually forgot, worked fine when I was powering over USB, but it blew it out when I tried one of my DC plugs :roll_eyes:

I'll never forget that again!

Actually it shouldn't light at all when just powered by the USB, however there does seem to be some +5vdc leakage current through the auto-voltage switching FET that was allowing the LED to light without damage. However when applying external power to the board with a LED without resistor you were effectivly short circuiting the external power module.

So I assume everything is working now as expected once the blue led was removed?

Lefty

Everything is working as it has been, the pin 9 led turns on and off, and when I am powered over usb I see my serial output, when powered over DC in I still just get the pin 9 led cycling and no serial output.

Everything is working as it has been, the pin 9 led turns on and off, and when I am powered over usb I see my serial output, when powered over DC in I still just get the pin 9 led cycling and no serial output.

And Vin measures what when on only external power?

retrolefty:

Everything is working as it has been, the pin 9 led turns on and off, and when I am powered over usb I see my serial output, when powered over DC in I still just get the pin 9 led cycling and no serial output.

And Vin measures what when on only external power?

Have yet to obtain a multi-meter.

Have yet to obtain a multi-meter.

Get a box and a roll of tape. Put the Arduino in the box, along with the wall-warts and everything else. Tape the box shut. Put it away.

When you get the multi-meter, you can get the box back out and open it. Until then, DON'T.