+ fact 1: we cannot use D1-D4 set. (D2 for LED, D4 for TXD1)
+ fact 2: using D5-D8 set again. (N.B. but to get proper stepping
sequence w/ accelstepper lib. u need to CROSS D6 and D7 wiring,
otherwise very poor torque & uni-directional not sane movements.)