martyscncgarage wrote: ↑Wed Jul 01, 2020 6:43 pm
Its very hard to do a schematic for every drive out there.
Rule of thumb, if the drive says use +5VDC for the +PUL and +Dir, then you should use the DB25.
Oh I know, the designs are probably limitless and always changing. I'm just a complete newbie so wasn't aware. But hopefully my post will help somebody else out too
this post helped me! getting ready to hook up my new acorn board to my CNC mill and I am also using the DM556T drivers. would be cool if there was a note on the acorn page that you need the DB25 for most stepper drives
so I am a little curious now... can I just use the headers on the acorn for ST and DIR? instead of getting a DB-25? or is there something special about the outputs throught the DB-25
Tklus wrote: ↑Fri Apr 30, 2021 5:00 pm
so I am a little curious now... can I just use the headers on the acorn for ST and DIR? instead of getting a DB-25? or is there something special about the outputs throught the DB-25
The DB25 works best for 5vdc logic drives. That's where you should connect. If you want to try it on the header terminals that's up to you....
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Using the DB25 connector is the PREFERRED method to connect a stepper driver to the Acorn; but, using the Open Collector outputs of the "H" connectors also works if you understand their limitations.
The schematics that I have for my DM542 clones show that the Step, Direction, and Enable inputs use Opto-Couplers rated to work properly with about 10mA current. At voltages higher than 5vdc, a current limiting resistor should be used. For 12vdc, use a 1K to 1.2K 1-watt resistor in series with the signal. For 24V, use a 2K to 2.4K 2-watt resistor in series with the signal. Using higher wattage resistors will help prevent burning the skin off your fingers if you "test" the temperature of the resistor with a finger tip.
An Open Collector circuit SINKS current which is why you must connect +5vdc to the "+" side of the signals. The Acorn pulls the "-" side of the circuit LOW when the circuit is active. The advantage of an Open Collector circuit is that you are not limited to 5V logic. Because an Opto-Coupler circuit works with current, with the proper limiting resistors, you can use a supply voltage of 12v or 24v. The DMM and ClearPath servo drivers that I've used have internal circuitry that allows you to use 5vdc or 12vdc or 24vdc without adding current limiting resistors.
One thing that is important to know is that 'Open Collector' means that the collector on the output transistor in an Open Collector circuit 'floats' until it is connected to a circuit. One side of your circuit is connected to a voltage source and the other side is connected to the transistor's collector. (Transistors have three leads or connecting points: the Base, the Emitter, and the Collector, hence the name 'Open Collector'.) The shape of the waveform viewed by an oscilloscope that is connected to the Open Collector is mostly determined by your circuit and not by the transistor. Using a resistor in parallel to the circuit or a reverse biased diode can help 'clean up' signals. That's where a DIYer needs to bench test his design until he gets the results he needs to make his project work as he expects it to work. Bench testing is much more than just verifying that something works, but that is a subject for another time.
Until fairly recently (about 10 years ago or so), digital logic using the 74xx series of chips were only viable when used to SINK current from 5vdc voltage sources. If you look at the stepper driver manuals for the Gecko G201 and G202 stepper drivers, you'll see that +5vdc is used as the "common" and that the step and direction terminal connections SINK current. The reason that the Gecko drives used a SINK circuit is that the original 74xx logic could SINK 10 to 20mA of current but could only SOURCE about 1mA (depending on the chip 'family' being used).
About the time that the Arduino, Raspberry PI and Beagle Bone computer/controllers were brought to market, chip design changed. The newer chips could SINK or SOURCE up to 100mA. About that time, Geckodrive introduced their very popular G203v stepper driver that used GND as common. The G203v specs stated that the driver circuit needed to be able to supply at least 2.5mA of current.
On my Acorn boards, I've connected the DB25 connector to the DM542 PULSE '-' and DIR '-' terminals connected to GND lines on the Acorns's DB25 connector and the DM542 ' PULSE '+' and DIR '+' terminals connected to the Acorn's STEP and DIR outputs on the Acorns' DB25 connector. I've also connected the DM542 PULSE '-' and DIR '-' terminals to the Acorn's DB25 Step and Dir outputs and the DM542 PULSE '+' and DIR '+' connected to +5vdc. Either way has worked as long as I properly configured the signal polarities in Wizard.
The Opto-Couplers that Leadshine clones use are usually considered to be 'slow' devices, so you need to limit the steps per second to 100,000 in Wizard. (I've safely used 200,000 with my DM542 drives. Your mileage may vary.) A 'slow' Open-Coupler circuit can sometimes be 'tuned' to handle faster signals by using reverse biased fast acting diodes across the inputs, but that's another subject. 100,000 steps per second is 3X faster than my old Shopbot PRT-Alpha could tolerate. 100,000 steps per second should drive any axis much faster than mills, lathes, and routers can handle if the driver is setup to use reasonable micro-stepping.
Last of all, as others have pointed out, the Enable input into many stepper drivers is really a "disable" input. When current flows through that circuit, the driver is disabled. I have always left the Enable signal disconnected on all the various stepper drives that I've used.
