QKits Electronic Kits: qk113, Two Unipolar Stepper Motor Driver Kit

Dual Stepper Motor Controller Kit - Electronic DIY kit

This kit enables users to control two unipolar stepper motors via a parallel/printer port of a PC. Four digital inputs are also included. These can be used for monitoring external switches and inputs. The kit itself does not require any power source. The stepper motors require power.

The kit is designed to fit into an extended D-shell plastic case. This is also called an RS232 plastic case. A DOS based program written specifically to drive stepper motors is included on disk, complete with C source code.

The kit is constructed on a double-sided, through-hole-plated printed circuit board (PCB). Protel Autotrax and Schematic were used to design the board.

CIRCUIT DESCRIPTION

The circuit consists of eight high-gain NPN transistors (Q1-8) that are driven via the eight data outputs of the PC printer port. The transistor outputs are open collector, which means that the load is connected between the transistor collector pin and a positive voltage source. Protection diodes (D1-8) are provided so that the back EMF generated when driving inductive loads, such as stepper motors, will not damage the transistors.

Four high voltage inputs (up to 15V) are also included. Any input voltage above 5.1 volts (nominal) will be clamped by the 5.1V zener diodes (Z1-4). Resistors, R1-4, provide current limit protection for the zeners.

The kit is really a digital I/O device with 8 active-low outputs and 4 protected inputs. The outputs can be used to switch relays, LED's, lamps or any other "on-off" device. It is the software provided with the kit that makes it a stepper motor controller.

STEPPER MOTORS

Stepper motors are a special type of motor. Instead of rotating smoothly, they move incrementally - in steps. Each step is a fixed angular displacement of the motor's shaft. For example, if the step increment is 3.6º, then 100 steps are required for a complete 360º rotation of the shaft.

There are two types of stepper motors:

1. Bipolar motors. These have two coils and are controlled by changing the direction of the current flow through the coils in the proper sequence. These motors have only four wires and cannot be connected to this kit. They are declining in availability.

2. Unipolar motors. These have two center-tapped coils which are treated as four coils. these motors can have five, six or eight wires. Five-wire motors have the two center-taps commoned internally and brought out as one wire. Six-wire motors bring out each center-tap separately. The two center-taps need to be commoned externally. Eight-wire motors bring out both ends of each coil. The four "center-taps" are joined externally to form one wire. In each case the center-tap(s) are connected to a positive motor power supply.

	~ Celebrating 12 Years of QualityKits in 2008 ~		25-Jul-2008