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February 2018, announcing rt-stepper dongle REV-2. This dongle has a separate RJ-11 connector which provides a modular way of connecting the rt-stepper sensor kit, limit switches and two digital outputs. This new hardware is backward compatible with old hardware and works with the current software. Plus the new dongle is more than 20% smaller, see the new dongle on the left compared to the older dongle on the right.

December 2017, announcing PyMini software release 2.6. PyMini now supports spindle synchronization for G33 and G76 threading commands. Synchronization requires INPUT0 index pulse and dongle FW 1e. CAM support for threading is available with Fusion 360 using a custom post processer. See the threading sample code using Fusion 360.

September 2017, announcing PyMini software release 2.3. Made a user functionality change to Absolute Jog in PyMini. When in Absolute mode the Jog buttons are now defined +/- similar to the Increment buttons. Use the "-" button to jog in the negative direction, the "+" button will jog in the positive direction. Made changes to the PyMini backplot panel in order to make the tool path display more accurate. Backplot panel now supports circular commands G3/G2. Before they displayed as straight lines.

August 2017, announcing PyMini software release 2.2. This release provides the following new features.

  • The GUI can now display spindle speed in RPM. Spindle speed can be measured by connecting a index pulse to the rt-stepper dongle INPUT0 pin.
  • An appropriate index pulse can be generated with the new rt-stepper sensor kit. The kit provides all the necessary hardware for mounting to a Sherline spindle motor.
  • New updated rt-stepper dongle firmware (revsion 1d) provides support for spindle speed.
  • The GUI now provides a Tool Offsets screen for lathe parameters. This option is enabled in the rtstepper.ini file.
  • The rtstepper.ini file now uses the Sherline mill as default settings.

April 2017, announcing PyMini software release 1.18. Added support for Auto/Run cancel which will execute a synchronized stop. Once the last move has completed you can restart the gcode program without an All Zero command. This different from the EStop button which executes a un-synchronized stop.

February 2017, announcing PyMini software release 1.16. The Windows PyMini download now comes bundled with Python 3.5. This means all the PyMini software for Windows is contained in a single zip file. Windows 7 rt-stepper driver is now a separate download. Window 8 and Window 10 require no driver install.

March 2016, announcing new updated firmware for the rt-stepper dongle. The rt-stepper dongle is now plug-and-play compatible with Window 8 and Window 10. This means no driver install is required. Just plug in the dongle in and start using it with PyMini software. Except for the new embedded Microsoft support the dongle is functionally the same as the old dongle.


Eckler Software offers a unique USB solution for CNC controllers with the rt-stepper USB-to-Parallel dongle. Users can use the rt-stepper dongle to convert a parallel port CNC controller into a USB CNC controller. Designers can integrate the rt-stepper dongle hardware into there own CNC controller.

Most CNC controllers are designed to be driven with a PC parallel port. Unfortunately parallel ports are thing of the past and many new PCs have no parallel port. Commercial USB-to-Parallel dongles do exist, but these dongles are designed for printers not CNC controllers. CNC controllers require XYZ step/direction signals. With the rt-stepper dongle you can now drive XYZ step/direction signals over the USB bus.

Driving a CNC controller with a PC parallel port requires a real time OS otherwise the stepper motors can loose synchronization. With the rt-stepper dongle this restriction is removed. The rt-stepper dongle provides the real time stepper motor control which means you can now use your favorite OS such as Linux, Mac or Windows. Each dongle provides a step resolution of 46,875 Hz.

Most commercial gcode interpreters do NOT support laptops with parallel port chipsets. This is not a problem with the rt-stepper dongle. You can use any Linux, Mac or Windows laptop or netbook with USB support. Laptops can provide dedicated CNC setups with minimal investment and work space.

PyMini is a powerful minimalist user interface written in python. A user can write their own gcode program using their favorite text editor or run a CAM generated gcode program on PyMini. You can verify the gcode program with or without the dongle connected and view the xyz paths executed on the backplot panel.

There is only one process that runs on the PC - PyMini. PyMini is a GUI front-end program that communicates to the dongle. Both manual and auto CNC operations are supported. PyMini main screen is showed below, for information see the PyMini documentation.

The PyMini software supports the same gcode interpreter and trajectory planner as EMC/LinuxCNC. See the "Gcode Overview" section at www.linuxcnc.org for gcode syntax. Note, mcodes are handled differently in PyMini. Most mcodes are implemented via python plugin scripts. This means spindle, coolant and homing can be executed via custom python scripts.

I started using EMC back in 2002. I developed this product after using EMC for several years with my Sherline CNC mills. EMC worked great, but requires a PC with a real-time kernel and a parallel port to control the mill. Now I have the best of both worlds EMC/LinuxCNC based software with no real-time kernel requirements.

I have two mills and two CNC controllers - Camtronics and Xylotex. I now use the PyMini software exclusively. I can use the latest notebooks, which have no parallel port, with my old CNC controllers.

Originally I built the dongle PCB on my mill. Now the dongle PCB is made at a local USA circut board manufacturer, but I still make the custom case with PyMini. You don't get a feel for a product unless you use it.

I used Eagle CAD to develop and build the PCB. The engraving software I used for the case is called engrave-11-inline. Engrave-11-inline is a good example of using a real programming language, in this case python, to develop gcode output.





Buy one rt-stepper dongle, no case $59 + 5.35 shipping (US address only).
Buy one rt-stepper dongle, no case $59 + 16.95 shipping (non-US address only).
Buy one rt-stepper dongle with sensor kit, no case $76 + 5.35 shipping (US address only).
Buy one rt-stepper dongle with sensor kit, no case $76 + 16.95 shipping (non-US address only).




Buy one rt-stepper dongle with case $79 + 5.35 shipping (US address only).
Buy one rt-stepper dongle with case $79 + 16.95 shipping (non-US address only).
Buy one rt-stepper dongle with sensor kit and case $96 + 5.35 shipping (US address only).
Buy one rt-stepper dongle with sensor kit and case $96 + 16.95 shipping (non-US address only).




Buy one rt-stepper sensor kit $22 + 5.35 shipping (US address only).
Buy one rt-stepper sensor kit $22 + 16.95 shipping (non-US address only).

The rt-stepper sensor kit creates the index pulse for measuring the spindle speed. The kit as shown in the above picture provides all the necessary hardware for mounting to a Sherline spindle motor. Each kit bolts on to the DC speed controller case with no modification made to the Sherline equipment. Use the above picture for reference when installing.

The plastic sensor mount is made out of ABS. The black disk with reflector tape is made out of light absorbing black construction paper. Since the disk center hole is a tight fit it can be placed on the spindle pulley with or without using a glue stick. The 3/4 inch socket head screw replaces the original 1/2 inch socket head screw.

Use the provided RJ-11 cable to connect the sensor board to the rt-stepper dongle. No additional wiring is necessary for the sensor when using the rt-stepper dongle with RJ-11 connector. The generated index pulse is connected to the dongle on INPUT0 (DB10). A straight through RJ-11 cable is required not a reversed wired cable.

For optimal sensor sensitivity the distance between the sensor and the black reflective disk should be 1/16 inch (0.0625). After tightening down the sensor mount make sure the distance is correct. The mount is slotted so you can adjust it up or down with the socket head screw.




Buy one rt-stepper dongle breakout board $29 + 5.35 shipping (US address only).
Buy one rt-stepper dongle breakout board $29 + 16.95 shipping (non-US address only).

The rt-stepper dongle breakout board is available for breadboarding or hard wiring your own connectors. This is a REV-2 dongle that supports all the same functions as the regular dongle. It includes the same USB connector, but no DB25 or RJ-11 connector. The above picture on the left shows what is included with the breakout board. Each board comes assembled and tested, but the two 10-pin headers are NOT soldered to the PCB board. You will have to solder in the 10-pin headers yourself. Reference the above picture on the right for pin identification. By convention each pin number corresponds to a DB25 connector pin signal. See the PyMini documentation on how these signals are used.

PIN NUMBER    NAME
2             DB2  (DB2-9 are step/direction signals)
3             DB3
4             DB4
5             DB5
6             DB6
7             DB7
8             DB8
9             DB9
10            DB10-INPUT0  (index pulse)
11            DB11-INPUT1  (limit switches)
12            DB12-INPUT2
14            DB14-OUTPUT0
16            DB16-OUTPUT1
The board provides 5V and GND from the USB bus. Care must be taken to NOT exceed USB 1.1 bus power specification.

Save on shipping with multiple orders to the same address. Actual shipping will be adjusted to a single shipping charge (at shipping time).


The rt-stepper dongle hardware is based on the Microchip PIC18F2455/PIC16F1459 processor. If you are board designer and would like to integrate the dongle hardware into your own application. I am willing to sell you preprogrammed pic chips for your application. Based on my sublicense agreement with Microchip this arrangement works best because each pic chip must be programmed with unique USB descriptors (ie: pid/vid, serial number, product ID).

Be sure to use the rt-stepper dongle as your reference design with your application. Because any hardware or software support would be based on the dongle only. Please email me for more information.


© 1996-2018 Eckler Software

Last updated February 5, 2018