[windell747]

Why do you need to have such a high switching rate for the transitors? You shouldn't need to count pulses using electronics since the speed of the processor is so high and all the inputs are read simultaneously. The inputs are read at something like 38kHz. This limits the max freq of the encoder pulses to at most 19kHz. That is a rate of about 80 rev/sec of the encoders or 4800rpm.

If you really want to do it using ICs why not use a counter chip or build one using a shift register?