Because these LEDs have a common cathode, their anodes are connected to the emittor of the BC847 transistors. The voltage on the collector of an NPN transistor can only be V(b)- 0,7V. The current circuit is very limiting for the current flowing through the LEDs.
Better would be a FET instead of a transistor (with pull-up resistor at the gate), and an open-drain output.
Because these LEDs have a common cathode, their anodes are connected to the emittor of the BC847 transistors. The voltage on the collector of an NPN transistor can only be V(b)- 0,7V. The current circuit is very limiting for the current flowing through the LEDs.
Better would be a FET instead of a transistor (with pull-up resistor at the gate), and an open-drain output.