Sensebender micro failing with funny characters

[flix]

Hi All,
I have an issue with a sensebender micro temperature and humidity sensor that I am looking for tips on how to troubleshoot.
For about 7 months the sensor has been working fine (with the odd transmission failure, as it is some way from the gateway), but it recently started transmitting data intermittently, and today completely stopped. I hooked it up to a serial monitor (Arduino IDE version 1.8.12 running on Kubuntu 20.10) and realised that there are multiple unknown characters (reverse question marks, see attachment) being sent. I've read that this could be due to an incorrect baud rate, however it is set to 115200 baud and works fine with other (identical apart from the node number) sensebender micros I have running.

I have done the following to try and troubleshoot it:

• Replaced the NRF24 radio with a brand new one (from Itead.cc, where I bought the Sensebender micros), but no change in the serial output or transmission

• Replaced the NRF24 radio with one from one of my other working sensebender micros, but no change in the serial output or transmission

• Re-uploaded the Sensebender Micro sketch (this has fixed the same issue once on another sensorbender micro), but no change in the serial output or transmission

• Cleared the EEPROM using the MySensors 'ClearEepromConfig.ino', and then re-uploading the Sensebender Micro sketch, but no change in the serial output or transmission

While I won't rule it out, I don't think it is a power supply or radio issue, given it was working fine previously / I've tested other radios. While the serial monitor indicates there are transmission issues, I can confirm that the gateway is also working correctly, as my 4 other sensebender micros are successfully transmitting to it.

Would it be worth re-flashing the bootloader onto it? Any other ideas I could try out? This is the 3rd sensebender micro I have displaying this issue, has anyone else come across it?
Thanks in advance for the tips!

[Grubstake]

@flix said in Sensebender micro failing with funny characters:

I don't think it is a power supply or radio issue, given it was working fine previously

"It was working just fine before" is pretty much the case with 100% of failures! It sure looks like you covered all the likely culprits EXCEPT the power supply. Software seems unlikely. Are you testing while powering the Sensebender from a USB cable to your computer? Try different USB cable and/or a different USB port directly on your computer (not a hub). A bad USB cable could have trouble with either power or data. You might also test with battery power directly to the board if external usb power is the usual mode.

[flix]

The Sensebender is normally powered by 2 x AA NiMH, and at the time the node stopped transmitting data, the voltage was at 2.6V. Powering it again by batteries, there is no data coming from it.
Obviously, to read the serial output, I've connected it to my computer and powered it via the USB port only (no hub in between). I use the same cable and FTDI module to successfully power and read my other Sensebender's, nonethelss I tried different cables and USB ports on my computer without any success.

[alexsh1]

@flix I have seen these issues with some boards. Garbage is coming from the serial output and nothing is transmitted. Any sign of moisture ingress? You may try to re-solder the atmega328p with a hot gun but this most likely would required de-soldering all the wires from the board. Please check other things - bad soldering connection to VCC or GND may give a similar error. Maybe some bad soldering joints? You may want to try 9600 rate to make sure it works. On some boards to had to re-upload the boatloader (fake atmega328p IC).

The last resort of nothing works - change atmega328p. If the power is fine and no probs with the transmitter and no bad joints, most likely it is the IC

[flix]

@alexsh1 Thanks for the comment, there is some good tips there! I'll try re-soldering some of the connections. Funnily enough, I had wanted to increase the transmission power on 2 of my nodes (the furthest away from the controller) including this one here, and had added that at the top of my sketch. After uploading the sketch, the serial monitor still displayed a lot of garbage, but the node started successfully transmitting temperature and humidity values!

So I've put the batteries back in and hung it up in the room, and it has been running pretty good so far. But I have my doubts how long it will last, given I didn't actually fix the serial output issue...

On another note, is there anyway to confirm that the transmission power has been increased? I added
#define MY_RF24_PA_LEVEL RF24_PA_MAX
at the top of my sketch, just after defining the radio type, but it doesn't seem to have improved my transmission success rate (I realise there are lot of other factors affecting transmission success, but just wanted to check)...