Electronic – Powering the blue pill board from laptop and using another power supply at the same time, will this cause problems

circuit-protectionpowerpower supplyshort-circuit

The components: a laptop, a blue pill board, a +5V power supply(taken from old PC).

I have a blue pill board(stm32f103c8t6 mcu). Schematic here.

I connect my laptop to the blue pill board via SWD interface(CN4 on the schematic) using an ST-LINK v2 debugger. So the board gets its power from the 3.3V coming out of the ST-LINK. I set PA0 to output a PWM signal. Now, I will connect it to the servo motor. Making the following connections:

SERVO side – blue pill side

signal cable – PA0

GND – GND

Connections are done, then I also connect GNDs of the 5V power supply and the blue pill board. So I made all grounds common.

Finally, I will connect +5V output of the power supply to the +5V input of the servo. This is the connection I suspect might be problematic. I don't know whether using these two power supplies(one through laptop and the +5V power supply) to power different parts of the circuit will cause problems(short circuits, harming the laptop or mcu, etc.) or not. Any explanation would be nice.

p.s: I am not able to draw a schematic now, sorry for it.

Best Answer

This works fine on the Arduino using a CNC shield from USB 5V with 12V power or laptop charger 19.5V with good common grounds.

However if the signals are on long cable, you may experience errors on Data if the charger is connected from Charger Common mode noise.

If you sequence power while connected the unpowered digital interface may have problems if un protected , so a series R of 10k will protect it but may reduce noise immunity and high speed limit. USB is safe but perhaps not unknown logic interface.

But from your comment an old PC PSU that has all the 12V power and logic level supplies should suffice with no other supply needed.