DIY video dolly stepper motor driver

  
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The ubiquitous 555 timer, (hooked up for variable mark/space ratio, if you build one you`ll find out why it`s needed), and a couple of D type flip-flops, (4013), to provide the count for the ULN2003 stepper motor driver. (ULN2003`s might be hard to find off the parts shelf nowadays, this one was stripped from an old printer board but a ULN2803 or
DIY video dolly stepper motor driver - schematic

similar will do a nice job). The 4013 provides a 0011 and 0110 count required for the boot-strapped ULN2003, a DPDT switch providing forward and backward drive, (by simpling reversing the connections). The ULN2003 is hooked up in such a way as to provide dual coil drive for a unipolar stepper motor so that it gains more torque to drive the `dolly`. A 7805 regulator to provide 5 volts for the 555 timer and flip flop, (the stability of the 555 timer is much improved by doing this!), and the 12 volt from the battery pack driving the stepper motor. The timing capacitors on the 555 are a tantulum, (1uF), and myler, (0. 22uF), types to further aid stability. Could it be better Yes, definately. I was going to use a 4017 decade counter hooked up with diode logic to provide half step driving to the stepper motor with a further output to fire the camera when the rail is not moving, but the scrap 4017 counter I lifted from a scrap board had a faulty output so that idea was put to one side. Who knows, maybe I`ll get into this and put something more luxurious together. Or maybe not and I wouldn`t have wasted too much time and definitely no money. Nice.