STM32 Nucleo F103RB: LD1 slow blinking with external supply

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I'm trying to use a Nucleo F103 RB (stm32) with an external supply (5V) but it seems it can't work because the led LD1 is blinking slowly between RED and OFF. According to the manual, it means "At power-on before USB initialization". I'm afraid I don't know what it means. Before connecting the Nucleo to the external supply, I had flashed the corresponding software using Keil uVision 4 by connecting the Nucleo to a PC via USB. There, I debugged the program and it ran correctly on the Nucleo. LD1 remained RED, not blinking. I've tested other Nucleo F103RB samples with my program and also with other programs and I've had the same problem: working fine in debug mode with PC supply but not working with external supply. When I connect the Nucleo to the PC, I switch the jumper on U5V. When I connect an external supply, I switch the jumper on E5V.

Has anybody faced this problem? Thank you in advance!

Best regards

EDIT: Finally, it worked despite that LED blinking. The problem seemed to be an app which worked through Modbus. Thank you both for your help anyway ;)

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stm32nucleo
A picture of your setup would be nice. ;-) Is the jumper JP1 ON or OFF? It must be OFF. Did you connect the external power to the PIN 6 of CN7. If you use VIN (pin 24 of CN7 or pin 8 of CN6) you must apply at least 7 Volt but not more then 12 Volt. LD3 must be ON. Ah, and you must connect the ext power before you connect the board to USB (if you do). – Peter Paul Kiefer

1 Answers

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I wonder if your examples run connecting the board to the PC just to provide power not under debugging mode.

Also, here quoting the manual :

The power supply is provided either by the host PC through the USB cable, or by an external source: VIN (7V-12V), E5V (5V) or +3.3V power supply pins on CN6 or CN7. In case VIN, E5V or +3.3V is used to power the STM32 Nucleo board, using an external power supply unit or an auxiliary equipment, this power source must comply with the standard EN-60950-1: 2006+A11/2009, and must be Safety Extra Low Voltage (SELV) with limited power capability

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