Custom board works on USB power; not on other power supply.

[XooM]

 uint32_t currentTime1 = HAL_GetTick();

	          // Her 1000 ms'de bir işlem yap
	          if (currentTime1 - lastTime >= 500)
	          {
	              HAL_GPIO_TogglePin(GPIOB, GPIO_PIN_14);  // LED'i toggla
	              lastTime = currentTime1;                  // Son işlem zamanını güncelle
	          }

"I am using an STM32F100 MCU in my own PCB design. When I run it through the computer's USB, the LED toggles. However, when I power it with an external power supply, the LED just turns on and doesn't toggle afterward. I have no idea what could be causing this. Could you help me with what I should check?"

[Tesla DeLorean]

Check state of BOOTx pins.

Check VDD and VDDA, check state of NRST

Have output via UART or other GPIO or LEDs if you end up in Error_Handler or HardFault_Handler. 

[XooM]

"When I power the system through the USB port, the LED toggles. However, when I apply external voltage without disconnecting the USB, the LED stops toggling. Could the points you mentioned still be relevant to this issue?

[Andrew Neil]

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@XooM wrote:

my own PCB design

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Show your schematic.

Give details of the "external power supply" - have you verified that it gives a good, steady output?

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@XooM wrote:

when I power it with an external power supply, the LED just turns on and doesn't toggle afterward

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In that state, can you use the debugger?

PS:

Have you reviewed your custom board design against Application note AN2586, Getting started with STM32F10xxx hardware development:

Getting started with STM32F10xxx hardware development - undefined

Also check against ST board designs (Discovery, Nucleo, et al)