24-10-2015, 17:09
I have been using several types of power supplies, inclusive cheap chinese ones, and I never seen this behaviour. As AllyCat said, maybe you are facing a strange RFI problem.
Having the two PSU and USB power "fighting" each other, not seems to be the problem.
The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.
"The board has a simple two resistor voltage divider wired to the Vin voltage, if there is a voltage of sufficient voltage, a op-amp comparator circuit switches off a MOSFET switch that then isolates the USB voltage from the board's Vcc bus. So if there is both USB voltage and Vin voltage available, then the Vin voltage takes priority and is used to power the board. "
When powered by the external 12V power supply, the 9V from the 7809 regulator is applied to Vin (pin 30), so as this voltage is greater than the USB power voltage, its automatically selected to feed the Arduino.
Just for testing, try AllyCat sugestions:
Try a separate "mains adapter/charger", or another PC, is possible try also a shielded USB cable with ferrites.
Having the two PSU and USB power "fighting" each other, not seems to be the problem.
The Arduino Nano can be powered via the Mini-B USB connection, 6-20V unregulated external power supply (pin 30), or 5V regulated external power supply (pin 27). The power source is automatically selected to the highest voltage source.
"The board has a simple two resistor voltage divider wired to the Vin voltage, if there is a voltage of sufficient voltage, a op-amp comparator circuit switches off a MOSFET switch that then isolates the USB voltage from the board's Vcc bus. So if there is both USB voltage and Vin voltage available, then the Vin voltage takes priority and is used to power the board. "
When powered by the external 12V power supply, the 9V from the 7809 regulator is applied to Vin (pin 30), so as this voltage is greater than the USB power voltage, its automatically selected to feed the Arduino.
Just for testing, try AllyCat sugestions:
Try a separate "mains adapter/charger", or another PC, is possible try also a shielded USB cable with ferrites.