The last two decades have seen enormous development of CNC control systems based on PC computer as control unit. Thereby, parallel printer port (LPT), because of some of its hardware features has been imposed as a port for communication between CNC controlling electronics and PC computer. On the other side, Mach series of software packages from Artsoft company, which is among the first who managed to provide "smooth" generation of STEP/DIR pulse train, has become standard among software that turns PC computer into CNC controlling unit. Above facts lead to current situation where tremendous number of machines which use described control scheme are active.
Parallel port will in few years celebrate its 50th birthday. For many years this port is suppressed from laptop computers, and in recent years it is getting harder to find it also on desktop computer configurations. Users, technicians, also makers of new CNC machines that use described control method, are considering how, with as few as possible changes on existing system, to migrate to one of currently available ports, primarily USB port.
One possible approach to solve described problem is to use USB-MC motion controller and connection to existing systems that use LPT port is possible in two ways that will be described in further text in more detail.
USB-MC motion controller and LPT cable
USB-MC motion controller is designed so that it can be used as USB to LPT converter because it has integrated 25 pin female DB connector. Pinout of this connector is compatible with standard PC computer LPT port. Thus it is possible to use existing standard LPT cables. On the photos it is shown how it is possible to connect USB-MC motion controller to breakout board IO3-R2.
NOTE: Breakout board IO3-R2 has been replaced with breakout board IO3-R3.
http://www.audiohms.com/en/blog/item/153-usb-mc-with-existing-cnc-control-systems#sigProId33e8551e06
USB-MC motion controller and user cable – IDC40 to Centronics
Previously described way of connecting motion controller USB-MC to existing input-output cards has a few drawbacks. As parallel port is slowly being suppressed from modern computers, it is getting harder to find LPT cable available in offers from hardware suppliers. Other shortcoming is cable length. It is almost impossible to find LPT cable shorter than 1.5 m. If it is needed for USB-MC controller to be close to input-output board, cable length should be reduced in some way.
To overcome described drawbacks it is possible to use male 40-pin IDC connector that is available on USB-MC motion controller. In this case it is needed to make an "IDC-40 to Centronics" cable and connect USB-MC controller to input-output board as shown on photos.
http://www.audiohms.com/en/blog/item/153-usb-mc-with-existing-cnc-control-systems#sigProIdb2eaab5e49
Setting up Mach3 software
Mach3 uses files with extension XML for storing configuration. These files are located in the same folder where Mach3 executable is located (usually C:\Mach3). On program startup, user can choose XML file from which the configuration is loaded and later every adjustment that is made during that session are saved to that configuration file. It is possible to have multiple XML files for different configurations and use them as needed.
In the following table two configurations are given for setting up Mach3 software package using XML file. After downloading, archive with XML file should be unpacked to Mach3 folder. It is almost certain that further additional adjustments should be made for application to specific CNC machine (e.g. limit switches configuration, steps per unit for axes and similar).
IMPORTANT NOTE: Existing XML file should be backed up before it is overwritten with a file downloaded from this page.
More details about adjustments can be found in user's manual for USB-MC motion controller and input-output board IO3-R2.
| Download Mach3 configuration file | Description |
 USB-MC_to_IO3-R2_ChargePump_2Relay_LSW |
Basic adjustments:
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| USB-MC_to_IO3-R2_ChargePump_AnalOut_LSW |
Basic adjustments:
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How to make cable IDC40 to Centronics?
Second mentioned way of connecting USB-MC motion controller with input-output board, is using cable IDC40 to Centronics 36 pin which, with a little effort, can be made.
NOTE: Click on a photograph for larger view.
Required materials and tools |
Required materials and tools are shown on photograph. |
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IDC40 connector, flat ribbon cable and Centronics connector |
Following components are needed for making the cable:
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IDC40 connector, flat ribbon cable and Centronics connector |
Flat ribbon cable should be cut to a desired length. In this case it is 150 mm. It is important to note that final length of the cable will be approximately 20 mm less than starting length. |
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Preparing flat ribbon cable |
Considering that IDC40 connector has 40 pins and Centronics connector only 36 pins, it is required to prepare flat ribbon cable. At one side of the cable, about 25-30 mm in length, cut wires as shown on photograph. It should be noted that it is required to remove 4 conductors at the opposite side of the one marked by red conductor. Red color marks conductor that is attached to pin 1 on both connectors. |
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Fitting Centronics connector to flat ribbon cable |
Place flat cable, with side that has 4 conductors removed, in Centronics connector. Pin 1 on connector should be on the side with red conductor on flat cable.
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Placing Centronics connector with ribbon cable into the clamp |
Centronics connector with cable should be placed in to the clamp. It is important that clamping force is applied evenly across the surface of top part of Centronics connector. Proceed with clamping action until rise in resistance is perceived while turning clamp handle.
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Centronics connector after clamping |
After clamping, Centronics connector is firmly attached to the ribbon cable. Bend flat cable over Centronics connector and place top bracket (remaining blue plastic part that can be seen on photograph on the right of the Centronics connector).
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Centronics connector with placed top bracket |
Positioned holder that prevents dismantling of Centronics connector and flat cable. |
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Fitting IDC40 connector to flat ribbon cable |
Other side of flat ribbon cable should be placed in IDC40 connector. Make sure to orient the connector in a way so that the red conductor of the flat cable is placed on the side where pin 1 of the IDC40 connector is located.
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Placing IDC40 connector with inserted flat ribbon cable into the clamp |
IDC40 connector with inserted flat cable should be placed into the clamp. As mentioned in previous case, take care that clamping force is applied evenly across the surface of the top part of IDC connector. Proceed with clamping of top part until rise in resistance is perceived during turning of clamp handle.
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IDC40 connector after clamping |
After clamping using the clamp, IDC connector is firmly attached to ribbon cable. |
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Bend over flat ribon cable and place top bracket |
Bend over flat ribbon cable over IDC connector and fit top bracket (remaining black plastic part).
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Final cable appearance |
IDC40 cable is finished and ready to be used. As mentioned, final length of the cable is about 20 mm less then initial length of flat cable. |
Audioms Automatika doo Support team
