Hi all, a new member here and new to electronics too...
I'm a bit puzzled by the behavior of my 2N3904 transistor switch - probably missing something very fundamental.
I have a device with a digital pin terminal and I'm trying to pull down voltage on the control pin (5V). If I do it just by shorting it to the ground on this terminal it works fine (trigger received). When I try this with 2N3904 (pin@5v to C, E to device ground and external 5V to B; taking 5V from Arduino) it works only if have the common ground (device GND linked to Arduino GND). If I don't connect to Arduino GND the transistor is able to drop only 1.2V (5 -> 3.8V) and the trigger is not taken.
I'm not sure if I understand why this happens from the perspective of a mechanism....
Could someone explain that to me, please?
I'm a bit puzzled by the behavior of my 2N3904 transistor switch - probably missing something very fundamental.
I have a device with a digital pin terminal and I'm trying to pull down voltage on the control pin (5V). If I do it just by shorting it to the ground on this terminal it works fine (trigger received). When I try this with 2N3904 (pin@5v to C, E to device ground and external 5V to B; taking 5V from Arduino) it works only if have the common ground (device GND linked to Arduino GND). If I don't connect to Arduino GND the transistor is able to drop only 1.2V (5 -> 3.8V) and the trigger is not taken.
I'm not sure if I understand why this happens from the perspective of a mechanism....
Could someone explain that to me, please?