Stepper Motor Driver

Posted on Feb 5, 2014

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. For the purposes of this page the direction control function is selected by an ON-OFF-ON type toggle switch. This could be easily rep

Stepper Motor Driver
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laced by another method such as transistors controlled by a PC`s parallel output port. Speed control is by means of a potentiometer but the circuit could accept pulses or controls from other sources such as a push button or a simple computer interface. The direction could also be controlled by a computer interface. This web page uses integrated circuits from the SN74LSxx family of TTL devices. It is not the purpose of this page to provide detailed explanations of how these devices work and an understanding of simple logic circuits would be helpful. N. B. - Due to the lack of error detection or correction this circuit should not be used for application that require accurate step control or positioning accuracy. The circuit is intended for hobby use only. A testing version is shown near the end of this page. It is laid out differently and shows the SN7474 in logic block form and LED`s are used to indicate the motor coils being switched. Each time the CLOCK pulse goes positive the HIGH state at the SN74194`s OUTPUT terminals, (PIN`s 12, 13, 14, 15), is shifted either UP or DOWN. Refer to the "Stepper Motor Driver Waveforms" diagram. The direction of this shifting is controlled by switch S2. When S2 is in the center OFF position the HIGH output state will remain in its last position and the motor will be stopped. The pulses from the OUTPUT`s of the SN74194 are fed to four segments of the ULN2003 Driver. When a segments input is...

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