CNC Project Y Axis Z Axis Wiring

New Stepper drive Jan 2008

The Parallel port a 25 pin d type connector that you connect to the printer, has a multitude of functions depending on what software is controlling it, in this instance i am using MACH2, which seems to be (in my opinion) one of the most usable free downloads on the net, and can be used to generate a maximum of 1000 lines of G Code without having to buy it, it runs well with Windows operating systems such as XP.

The outputs of the parallel port are assigned from within the soft ware and will guide you through all of the steps required to correctly set it up, unfortunately there are only 5 inputs on each printer port and to address both limits on each axis plus an emergency stop 7 inputs are required, however the control software sets provision for extra ports and in this design i have used two ports by adding another printer port card to my computer, i have attached a drawing of the pins i have assigned to what function.

You could of course use any combination and wire the control circuit how you like providing in's and out's are not mixed

see attached port assignment drawing

The Stepper drivers i am using are obsolete but use discrete components and 4000 series logic chips, and all are freely available as replacement parts should they be required, the input signals to the drives only need to be pulled to ground to operate.

The break out board is something that all CNC machines need but it is often very difficult to find out about, Believe me I have tried and circuits of these are even harder to find. So with a bit of thought i came up with the circuit attached in PDF format, it is very simple and can be built on standard 0.1inch vero board I felt that the PCB could wait until the machine is finished them i might be able to route one out.

All of the Stepper drivers and control circuits are house in a standard Vero case that is 3 U high case,( a "U" is approximately 1.75 inch) and makes a very tidy and easy to wire construction, it is important to be extra careful when building as a box full of rats nest wiring is next to impossible to service a year or so down the line when it stops working.

The last photo in this series shows the filtering that i have placed in line with the switched mode power supply this is to get the DC as smooth as possible not knowing what if any effects will be had when running stepper motors with switchers, so far either the filter is working well or the motors are unaffected by the switching spikes from the power supply

The control program I will be using is a windows based program called MACH2 a limited but fully working copy can be down loaded from their site, http://www.artofcnc.ca/DownLoads.html

This will be used with windows XP as this has proved to be a stable platform to work with; the I/O port is the printer port socket on the motherboard the input side ( feeds signals to the PC) is fed through an opto-isolated buffer as part of the control equipment and can be seen running along the bottom of the bread board.

The DC power is supplied from a 24 volt 50 Amp switch mode PSU, with additional filtering and smoothing to ensure a good clean DC supply,
Stepper drivers are PKS digiplan CD10 an obsolete part but one that is easily serviceable, Ever forced to eat ones wordes.............OOPS!!! the stepper drivers turned out to be quite unserviceable,( USLESS) I have decided to develop new drives are currently under development biased around the Allegro SLA7052M an all in one driver capable of running up to 3 amps.

Having now tested both the controller and stepper driver i am prepared to publish the schematic diagrams below 

SLA7502M Data Sheet a 3Amp stepper motor driver IC

Circuit diagram of the stepper motor driver

Circuit diagram of the controller interface

The Stepper drives seem to work with one small modification, I will be publishing the circuit soon and PCB's will also be available to order, I am still learning about stepper drivers and soon will have a working drive power pack.

Testing of the stepper drives is a success and work well next i will build all four driver boards and add the aluminium heat sinking, extra heavy duty load resistors have been added as the original were getting too hot.

This is the new stepper drive, looking from the top, the current limiting resistors are 26Watt wire wound aluminium clad units and are all wired with identical length wires to compensate for additional copper resistance losses and are mounted on an aluminium sheet 2mm thick to dissipate any heat into the side rails, there is a 20K preset pot fitted to the front panel used to set current limit for the motors in use. There are three settable links fitted to the PCB and these are use to swap the logic coming from the controller, it is possible that i may have inadvertently swapped the logic through the controller, better safe than sorry.

On the last photo above you will notice that there is a pin from the IC not soldered and bent up, this pin is designated as ( NOT USED ) I used the position to route out a thick copper track and simply bent the pin out of the way as the best option.

The first prototype stepper driver with black aluminium above will be used as a fourth axis to drive a rotary table or some other device not as yet thought of or in the worst case as a spare.

I have thought about the cost of these drives but the total was a bit scary, around the £40.00 mark, a bit more than what i wanted but it is mine!!!!!!!! and not another bought in bit.

OK the wiring on the machine is nearly completed, the next big hold up is going to be finding a small 19 inch electronic rack to mount the PC, controller Power supplies and somewhere to stand the monitor.

After many months looking for a 19 inch rack case i finally get one at the right price, so the controller is fitted the pc case is built and fitted the software is installed and most of the cables have been wired, next is to wire the power supply, this is a 50 Amp switch mode PSU and a large filter is being placed in the supply lines to remove as much of the noise as possible, this will be in the form of a pi filter with two large 48000uF caps and as many turns of wire as i can fit around a ferrite core ring.

Full circuit wiring will be available soon.

New Stepper drive

Component obsolescence!!

Ok there are two main problems with the design above, first i am picking up noise, which is manifesting itself into both x & y axes jittering, secondly there is impending component obsolescence, this has led me to completely re-design the electronics.

To this end i have designed a 4 Axis stepper driver board that will provide up to 10 Amps per channel, this is using a standard IC L297 with external FET transistors, this will enable a much higher current drivethan off the shelf stepper drivers but with the downside of only haveing 1/2 step as maximum step count.

The PCB is a 4 layer board which will enable at a future date to change the simple fet switches to full brighe control

STOP!!!

Ok hear is some truth, i have been working in electronics for most of my life and i can build most things electronic, i stop when i have to program it, However i must have wasted more money trying to save a few bucks by building the electronics myself and with the money i have spent i could have bought them from new twice over, DONT DO IT IT AINT WORTH THE PAIN!!!

I have to date built 4 controllers each better than the last, but the functionally and cost of ready built microstepping drivers is such from now i am leaving my soldering iron permenantly at work.

CNC Project Y Axis Z Axis Wiring