I am making a little home made electronics project.
The plan is to turn on a Red LED when a SCART input is sending an RGB signal. Pin 16 on a SCART cable is 1-3V when the input is carrying an RGB signal (according to wikipedia – in my case it actually sends 4.5V so I figure this is quite a flexible spec).
The circuit I have designed works….but I don't know if it is safe, or done correctly! Please see the schematic below:
I have 2 main questions:
- I don't seem to need the 1k Ohm resistor leading to the base of the transistor. I assume any voltage applied to the 2N3904 base will switch the circuit on…so this is just keeping a low current to prolong the life of the transistor?
- The circuit doesn't work unless I cannot Pin 21 of the SCART input up to the ground of the main circuit. I don't know if this is safe, or the correct way to make this circuit work, can you validate my decision here.