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Stepper Motor Driver BCMSSMD1 The stepper motor driver is based around a commercial stepper motor drive type SD2 manufactured by Digiplan. A clock that dictates the motor rotation speed is available internally when the biased toggle switch is in the INT CLOCK position or externally when this switch is in the EXT CLOCK position. The internal clock rate and hence motor speed can be adjusted via the INT CLOCK RATE control. The internal clock rate is intentionally set at a slow rate (aprrox 40 -1000Hz) so as to permit fine control of the stepper motor in the INT CLOCK position. Motor Power Dissipation If the clock is stopped (INT or EXT) current will still be flowing in the motor coils which can lead to heat dissipation that may damage the motor and the controller. The motor can be disabled, when no current is drawn in the windings, by use of the ENABLE/DISABLE toggle switch. It is recommended that if the motor is stopped for long periods the DISABLE position is selected so as to reduce power dissipation in the motor and controller External clock input The SD2 clock is typically 0V low 12V high. In order to accommodate TTL clock levels from a PC I/O port or similar device, a level shifter has been incorporated in the EXT CLOCK input line. TTL level signals need only be capable of sourcing 100uA in the high state when applied to the EXT CLOCK input. If higher voltage clock levels are applied to the EXT CLOCK input no damage will result but the internal clamp of the 5V1 zener diode in the level shifter will take effect and the input current at 15V will typically be 1mA. The step occurs on the falling edge of the external clock and the external clock should remain high for at least 10uS prior to this falling edge. 400 steps are required for one rotation. With the load of the viscometer attached to the motor the maximum clock frequency is 1.2 KHz for guaranteed driving of the motor. This equates to 3 RPS (1200/400). Front Panel DISABLE/ENABLE toggle switch ENABLE Motor turns under control of stepper driver DISABLE Motor free to rotate-no current in motor coils DIRECTION/REVERSE toggle switch DIRECTION Motor rotates in direction dictated by coil connections REVERSE Motor rotates in opposite direction to above EXT CLOCK/INT CLOCK biased toggle switch EXT CLOCK The biased position of the switch when motor speed is controlled by pulses at the EXTNERAL CLOCK input INT CLOCK User held (self return) position when motor speed controlled by internal SD2 clock INT CLOCK RATE multi-turn potentiometer Varies the rate of the internal SD2 clock MAIN ON Mains power switch and indicator REAR PANEL DRIVE TO MOTOR 5 pin DIN socket Output connection to stepper motor 1 Motor Phase B- 4 Motor Phase B+ 2 No connection 5 Motor Phase A- 3 Motor Phase A+ EXT CLOCK IN Input for external clock drive