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I need to control two bipolar steppers from one BX-24 connected to two L293D 4 channel drivers. I wish to control the motor directly but hate to give up 8 ports to do so, although this method is quite fast and I have done this with one motor. Does anyone have any experience using a 74HC59C shift register to do this? I think it will work fine and only requires 3 BX-24 ports but I am concerned about the potential slowness of the stepper versus manipulating the AVR registers directly. I think that shifting the 8 bits used to control the two motors into the shift register will slow down the steppers significantly. The steppers I plan to use are 5 degrees per step and I may need to use half-stepping so they could be even slower. Thanks, Ed |
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Experience using shift registers for stepper motor control?
Started by ●February 16, 2002
Reply by ●February 16, 20022002-02-16
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I don't know how you planned to control the shift registers, but if you use SPI, you can get the best possible speed, because data shifting is all done in AVR hardware. Check out the files area for my own software/hardware shift-register design. Maybe you can optimise a bit on that as well. Personally, I would find a stepper motor controller IC, hook it up to the motor driver and use the BX-24 just as a clock source, sending an exact number of pulses. (Actually this is a forthcoming project for an industrial inkjet print head system ;o) ) What speed have you been able to obtain using one stepper motor? My calculations have resulted in a max RPM for the 2 motors of just 96RPM at half step, using SPI at its maximum bit-rate of 1.85MHz... Cheers! Edwin --- In basicx@y..., "edstewbob" <edstewbob@y...> wrote: > I need to control two bipolar steppers from one BX-24 connected to > two L293D 4 channel drivers. I wish to control the motor directly > but hate to give up 8 ports to do so, although this method is quite > fast and I have done this with one motor. Does anyone have any > experience using a 74HC59C shift register to do this? I think it > will work fine and only requires 3 BX-24 ports but I am concerned > about the potential slowness of the stepper versus manipulating the > AVR registers directly. I think that shifting the 8 bits used to > control the two motors into the shift register will slow down the > steppers significantly. The steppers I plan to use are 5 degrees > per step and I may need to use half-stepping so they could be even > slower. > > Thanks, > > Ed |
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Reply by ●February 16, 20022002-02-16
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Edwin, Thank you very much for your answer. I will look into using SPI. For my application I am able to get about 120 RPM from a 400 step per rotation motor at full step increments using 4 output ports directly with the l293D. I also used the E-labs E1204 controller with 3 BX-24 pins: PWM, forward/reverse, full/half step. My application requires driving the motors with battery power so I wish to optimize power consumption. With a more direct control of the motor stator coils I can turn the coil power off when not required and the holding torque of the motor maintains position. With an external controller it seems to always maintain power to the coils and the batteries drain down more quickly. If I can use SPI to interface with the L293D then this will be a good solution. Ed --- In basicx@y..., "wolfchild76" <lulju@h...> wrote: > I don't know how you planned to control the shift registers, but if > you use SPI, you can get the best possible speed, because data > shifting is all done in AVR hardware. Check out the files area for > my own software/hardware shift-register design. Maybe you can > optimise a bit on that as well. > > Personally, I would find a stepper motor controller IC, hook it up > to the motor driver and use the BX-24 just as a clock source, > sending an exact number of pulses. (Actually this is a forthcoming > project for an industrial inkjet print head system ;o) ) > > What speed have you been able to obtain using one stepper motor? My > calculations have resulted in a max RPM for the 2 motors of just > 96RPM at half step, using SPI at its maximum bit-rate of 1.85MHz... > > Cheers! > > Edwin > > --- In basicx@y..., "edstewbob" <edstewbob@y...> wrote: > > I need to control two bipolar steppers from one BX-24 connected > to > > two L293D 4 channel drivers. I wish to control the motor directly > > but hate to give up 8 ports to do so, although this method is > quite > > fast and I have done this with one motor. Does anyone have any > > experience using a 74HC59C shift register to do this? I think it > > will work fine and only requires 3 BX-24 ports but I am concerned > > about the potential slowness of the stepper versus manipulating > the > > AVR registers directly. I think that shifting the 8 bits used to > > control the two motors into the shift register will slow down the > > steppers significantly. The steppers I plan to use are 5 degrees > > per step and I may need to use half-stepping so they could be even > > slower. > > > > Thanks, > > > > Ed |
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Reply by ●February 16, 20022002-02-16
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Ed, You can always disable the holding current by using ENABLE1 and ENABLE2 on the L293D (pin 1 and pin 9 on the DIP version). Pulling one of these pins LOW will disable the coil current. Maybe these 2 pins can be your friends if you cannot get up to speed using SPI. This seems very much the case, as I had made a wrong calculation of 96RPM maximum by assuming 144 steps per revolution, instead of 400! Edwin --- In basicx@y..., "edstewbob" <edstewbob@y...> wrote: > Edwin, > > Thank you very much for your answer. I will look into using SPI. > For my application I am able to get about 120 RPM from a 400 step > per rotation motor at full step increments using 4 output ports > directly with the l293D. I also used the E-labs E1204 controller > with 3 BX-24 pins: PWM, forward/reverse, full/half step. My > application requires driving the motors with battery power so I wish > to optimize power consumption. With a more direct control of the > motor stator coils I can turn the coil power off when not required > and the holding torque of the motor maintains position. With an > external controller it seems to always maintain power to the coils > and the batteries drain down more quickly. If I can use SPI to > interface with the L293D then this will be a good solution. |
