EAS Electronics

EAS Microstep is our single axis microstepping chopper driver board for stepper motors. It is based on the National Semiconductor LMD18245 3amp 55volt full bridge motor driver.

Microstep

Microstep manual (.pdf), schematic (.pdf), layout (.pdf) and parts list (.pdf).
Microstep silkscreen layout by part number (.pdf)

Specifications:
Microchip PIC 16F627 microcontroller based.
Drives 4,6 or 8 wire bipolar/unipolar stepper motors up to 3amps at 55volts per phase.
Can be flash programmed to support half/full steps plus 4, 8 or10* microstep modes.
Adjustable chopper current drive, no large external resisters required for stepper motor current limiting.
Automatic current reduction after 3 minutes of no step pulse activity.
Standard TTL step and direction inputs.
The LMD18245 driver has internal overcurrent and thermal shutdown protection.
Requires PIC hardware programmer to program microcontroller. Can be in-circuit programmed with on-board header.
Source code included.
Heat sinking required.
Professional quality board with silkscreen.

Also available is a parallel port Stepper breakout, or our latest optically isolated breakout board Opto Breakout.

* Using standard 1.8 degree 200 step/rev motors,
10 microstep = 2000 steps/rev
8 microstep = 1600 steps/rev
4 microstep = 800 steps/rev
half step = 400 steps/rev
full step = 200 steps/rev

Using higher microstep rates will decrease the chance of motor resonance affecting performance. Resonance can sometimes cause a stepper motor to stall at a particular step frequency rate. We recommend the 8 microstep version for most applications.

We do not recommend the use of a full or half step drive due to the likelihood of motor resonance. It is only available for those who require it for a specific application.

Performance:
Atleast 1500rpm using a old Superior Electric M091-FD09 150oz Nema 34 stepper motor. Stepper motor voltage set to 44volts, using 8 microstep mode and half winding hookup to driver. Computer hardware is a P2-500 PC running TurboCNC.

Using a external pulse generator, we were able to spin a Pacific Scientific P21NSXC 116oz Nema 23 bipolar stepper motor over 1600RPM using a 45Khz step pulse input rate, 8 microstep mode. It isn't recommended to use a step pulse rate higher than 45Khz due to the speed limitation of the PIC microcontroller. If you require faster motor RPM speeds, please check out our CPLD based stepper driver.

1300rpm is the maximum motor speed for 10 microstep mode.

Some stepper motors may only run 200-400 rpm due to high winding inductance and magnet/rotor design. Modern lower voltage stepper motors achieve much higher rpm speeds and should be used if high speed is required in your application.

Dimensions:
2.6" x 1.5".

Power requirements:
Requires external 12-55volt DC motor supply.

Works great with standard 24volt AC transformers. This is approximately 35volts DC after diodes and filtering caps are added to complete the power supply. We recommend using a unregulated linear power supply and not a switching type supply.

We have tested the LMD18245 driver chips continuously with a 44volt power supply. Although the driver chip can handle 55volts, there should be some safety margin for stepper motor induced back EMF voltage. We recommend no more than a 44volt supply for reliable and trouble free operation.

Price:
Bare PC Board: $10.00
Preprogrammed PIC's: $10.00

Please state which stepper mode you require- full step, half step, 4, 8 or 10 microstep version. Only one version can be programmed into the 16F627 at one time. We recommend the 8 microstep version and will ship this version if you do not state your preference.

Preprogrammed PIC's are only required if you cannot purchase or program your own. The source code contains the various 16F627 HEX files needed to program the microcontroller. The source code can also be re-compiled for newer 18pin devices such as the 16F628/16F88.

Ordering parts from Digikey

Minimum parts count for Microstep click on this link   http://sales.digikey.com/partsbin/view.asp?pb_glue=1007454

Full parts count for Microstep click on this link  http://sales.digikey.com/partsbin/view.asp?pb_glue=1007455

Since the source code is available freely, those who need custom microstepping modes or new features can add it themselves. Program is written in C, which makes it easier to modify than assembly. Any modifications, please send us a copy so we may post the code for others to use. This stepper board can also be used to drive two DC motors for a small robot. Programming the PIC to do this function is up to the end user though.

No assembled units or parts kit are available. Bare PC boards are in stock.

Please include $5 shipping and handling for destinations within the continental United States. All other areas, please contact us for shipping charges.

For those only interested in purchasing a single bare pcb board, shipping and handling can be avoided by sending us the cost of the pcb and include a self addressed stamped envelope with your order. Please attach three first class stamps to the envelope with your legible return address. We suggest using cardboard floppy disks envelopes that can be purchased at office supply stores. US only.

Stepper motor test video. Superior Electric M091-FD09 Nema34 stepper motor driven by Microstep Driver with 44volt power supply, 8 microstep mode. Computer is a P2-400 running TurboCNC. Stepper motor is spinning at a maximum rate of 1900RPM. This is the fastest step rate this computer parallel port can output steps, approximately 50,000 steps/sec. Higher step rates is possible by using a faster computer.

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