Unipolar Stepper Motor Driver

The purpose of this project was to develop a stepper motor driver for 2-phase unipolar stepper motors that has built in current control. The eventual target project for this driver is for my CNC milling machine that I am currently planning out. This needs a few elements that are combined to provide a full driver. Once this is established the curre
Unipolar Stepper Motor Driver - schematic

nt being supplied to the motor coils needs to be limitted in some way to stop melting anything. The obvious option here is to use a chopper circuit. Finally an intelligent controller is required to provide the correct number of steps for a required distance of travel. Many simply use a PC parallel port for this on CNC projects but I want this to be more of a stand-alone driver that can be used for other things. Ideally I will include ethernet control so that I can run the CNC machine remotely from the comfort of my living room instead of the cold garage and negates the need for a dedicated control PC. The device is based around an L297 driver IC that performs the translation step (ie takes clock and direction input and generates the correct output sequence for driving the stepper) and has current limitting abilities. Additional logic and driver circuitry is then added to drive the motor coils. Each motor driver is fully independant of the other drives and is controlled with its own clock and direction signals, has a seperate current limitter setting and should not interfere with each other. In reaching this final solution I went through many designs, some of my own, some through various searches on the net. The final design is a combination of a few of the most common designs that can be found on the internet. One useful site I used is there are some good designs of stepper drivers and also a bulletin board where people...

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