Probably the simplest, reversible drive circuit is the H-Bridge. Some BEAMbots use H-bridge motor drivers; many more use an H-bridge variant of some sort. Here’s a simple conceptual schematic:
Based on the SN74LS194 – Bidirectional Universal Shift Register the circuit is designed to drive UNIPOLAR type stepper motors and provides only basic control functions – Forward, Reverse, Stop and Speed adjustment.
The only step angle for this driver is the design step angle for the motor.
The circuit is not complex and is cheaper than many dedicated driver/controller devices and the parts are easy to find.
This page links to UNIPOLAR and BIPOLAR stepper motor driver pages. The drivers are designed for simple requirement applications and are made with parts that are available from a variety of sources.
Both of the stepper drivers are use a 74194 – Bidirectional Universal Shift Register from the 74LS or 74HC – TTL families of logic devices to produce the stepping function. A diagram at the bottom of this page shows the difference between the 74194 – UNIPOLAR and BIPOLAR stepping pattern generation.
The UNIPOLAR driver uses a ULN2003 – eight segment, darlington IC as its output device.
The BIPOLAR driver uses a SN74410 – four segment, Quad – 1/2 H-Bridge IC as its output device.
These stepper drivers have only basic control functions: Forward, Reverse and Stop and Step rate adjustment. The calculated Step rate adjustment range of the drivers is 0.72 (1.39 sec) to 145 steps per second. (Lower and higher step rates are also possible.)
The only step angle for these drivers is the design step angle of the motor itself. ’Half-stepping’ is not possible with either of the driver circuits.