As soon as I replace 5V of the emitter (from the Arduino) with an external 5V source and connect GNDs, the LED stops blinking and stays on.
an external 5V source and connect GNDs, the LED stops blinking and stays on.
I suspect that your external 5V source is an unregulated supply and is supplying rather more than 5V under the lightly-loaded conditions in which you are using it. In which case, either use a regulated 5V supply, or drive the PNP transistor from an NPN transistor which is in turn driven from the chip output.
Is using an NPN transistor an alternative option in your case?
Is it possible to fix it?
1) you can put the led + resistor to the pnp's emitter; simplest fix but requires rewiring.
Can you post a link with a circuit for a NPN transistor?
You need to get that "8.xV" down to 5V.Is there a 7805 in the house?
So its not possible to fix it and to keep the LED connected to ground?
The OP would still need to common up, so the Arduino/328 would also need to take supply form that 7805.
The NPN switch is a lot simpler and something like a 2N3904 will switch 200mA and they cost pennies.
On the wallwart it says 4.5V. I just measured 8.6V.I didnt know this before. Does it mean that I can use this wallwart to power the Arduino (because 5V sources are not suitable)?
Hi,I built this circuit:(Source, transistor)As RLoad I'm using an LED with a resistor. RB is 1k (is that correct?)The circuit is connected to an arduino pin that changes every second.This circuit works and the LED blinks.As soon as I replace 5V of the emitter (from the Arduino) with an external 5V source and connect GNDs, the LED stops blinking and stays on.I want to use the circuit to switch 7 LEDs without drawing the current from the Arduino, the LEDs' cathodes are connected to GND.