7 segment LED by scanning

First the scanning is done with turn on time around 15 cycles @ 8MHz and off time around 2 cycles. When the scanning is done so fast different digit of 7segment display appeared messed up, even with the correct voltage (waveform) at the pin. This may be due to the delay caused by the current limiting resistor to each segment or may be due to the turn-off delay of the transistors.

The scanning timing is changed to 10 msec/ digit and the display are quite clear and bright.

Voltage Reference using TL431

TL 431 requires 1 mA current. When the current to the TL431 is less than 1ma due to the current drawn by load resistors, the reference voltage will become less than 2.5V.