stm32f407vgt6 problem with UART

[syifnrl]

I have stm32f407vgt6 from devebox. At first, I wanted to do led blink and it worked fine when I supplied it with external power via 5V pins. Then, when I tried to use UART pin (PA_9, PA_10) to print something to USB to TTL module, it did nothing. UART pins only work when I connected micro USB on stm32f407vgt6. Does anyone know how to solve this?

[JTP1 · Accepted solution]

Hello. How do you feed the power when using UART without usb connection ? Is your ground missing from mcu to ttl/usb converter ?

[syifnrl]

I supply my stm through 5v pin and gnd pin from my 12v lipo battery, equipped with step down converter. Then, I only connect PA9 and PA10 to my USB to TTL module (I use CP2102 USB to TTL module from waveshare).

[JTP1]

Ok. Note that you also need gnd to usb/ttl module 👍 sounds that its missing if communication works after you connect another usb cable from pc to micro usb which connects pc gnd to mcu gnd.

[syifnrl]

Thank you! your advice is such a big help for my last year final project