Try using a (MosFet N-Channel Enhancement mode) to actually switch the LEDs on and off. Many fets can be connected directly to a microcontroller. (NOT all, check your datasheet)
For 50 of them, There may be a PIC that has 44 I/O pins but I'd suggest a different method.
Look into "Serial In / Parallel Out" Shift Registers. You can string them together end to end.
There is a Serial in pin and a serial Out pin and then (usually) 4 or 8 output pins.
There is also a /Latch/ or /Load/ pin.
Then by placing the on and off signals on a data line and pulsing a second line to provide a clock signal, you can load all 50 bits in 50 clock pulses. Then just send one more pulse to the /Latch/ pins and all 50 bits will load into the registers at the same time.
Tie a logic driven MosFet to each output and you can drive nearly any load.
With a system like this you can create a single board that has 8 drivers on it and then replicate that board 8 times to get 64 outputs.
The PIC doesn't care, it just sends out 65 bits and 64 clock pulses followed by a latch signal.
Many Pinball games and Slot machines operate all the lights and some of the playfield systems using this method.
-Mike
