Basic hookup

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1metalguru
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Re: Basic hookup

Post by 1metalguru »

So after a bunch of research on this topic on the forum, I have come to the conclusion that other than a few idiosyncrasies, either interface can be successfully used with most stepper drivers. There are issues with speed (drivers with cheap optocouplers), and max frequency of signals (also due to cheap optos), but overall the H2/H3 interface works well when using a 5v supply , or series resistors and 24v. In general, most of the posts claiming lost steps turned out to be wiring errors or incorrect voltages, not the fault of the Acorn board. So, I think I am going to pursue the H2/H3 interface model. The DB25 route might work, but the lack of enable signals and the height of the BOB preclude me using it in my application. I could use a cable and remotely mount the BOB, but this seems a bit klunky for my taste.

Anyway, thanks guys, and I will post the results after I get a board to test with. Most of the guys on the forum heartily advocate test benching everything, so that's the route I will take.

MG
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Re: Basic hookup

Post by ShawnM »

Gary Campbell wrote: Tue Aug 09, 2022 6:01 pm I only advise new guys on what my experience from building a few hundred controls has proven to work. I never care if they follow my advice.
You know the old saying right Gary, "you can lead a horse to water but you can't make him to use the DB25". :mrgreen:

I ordered a spindle from John today at AT and we talked fiber laser. Thanks for the lead.
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Re: Basic hookup

Post by suntravel »

If you want to use the Headers, I would suggest to use stepper drivers that are known to work with 24V logic like the CL57T and corresponding close loop steppers.

Uwe
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Re: Basic hookup

Post by Richards »

The Acorn is versatile. It has options that may seem to be redundant; however, following Centroid's recommendations is more likely to be trouble-free for the long term. That being said, I have used Gecko G203v, G202, G540, and DM542 on both the DB25 connector and on the Hx connectors. On the Hx connectors, I have used 5VDC with no current limiting resistors and 24VDC with 2K-2W resistors. With the max pulse rate at 100,000 pps, both methods worked. Now, here's the "gotcha". I looked at the signal traces with an oscilloscope. The clear winner, unless signal conditioning was used is the DB25 connector when using Stepper motors. The Hx connectors are Open Collector. An Open Collector circuit tends to distort a signal's waveform, rounding the shoulders of the signal. Digital signals are NOT 0v and 5V as many believe. The data sheet for any device will show its LOW voltage and its HIGH voltage. Typically, the LOW voltage is 0v to 0.7V and the HIGH voltage is between 2.2V and VCC. The data sheet will also list the expected "rise" time of a signal. That "rise" time coupled with the LOW and the HIGH signal levels is why using the Hx connectors is not recommended. The rounding of the signal greatly lengthens the rise time. A slow rising signal can oscillate, causing false steps. At the very least, if you decide to use the Hx connectors with a stepper motor, you'll need to install "pull up" resistors to sharpen the signal. Even better, you should use a Line Driver and a Line Receiver to condition the signal. (You'll find threads that discuss both "pull up" resistors and Line Drivers/Receivers.)

As for the DB25 connector adaptor board being bulky, that may be true. The work-around is to buy DB25M shells that use crimp type terminals. You crimp the terminal/pin to the signal wire and then insert the terminal/pin into the DB25 shell. The shell takes adds about 1/2-inch or less to the length of the Acorn.

The Acorn is DIY. Pick whatever method you want to use. As the designer, you'll know how to fix things when the unexpected happens.

It's too bad that Gary Campbell gives away valuable advice. His designs are rock-solid. If he charged $150 per hour for consulting, he would still be inexpensive. My adventure with Acorn started when I watched some of his YouTube videos showing how he was using Acorn boards. I looked around YouTube and found Marty and Keith and many others that had videos showing how to use the Acorn. The current recommendation from those experienced users is to use the DB25 connector for steppers and the Hx for most servos. I've run enough experiments to trust their recommendations. I've also built enough "interfaces" to know what would be needed to use the Hx connectors reliably with most low cost stepper drivers.
-Mike Richards
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Re: Basic hookup

Post by cnckeith »

DB25 5 volt TTL logic is designed for stepper drive most every stepper drive should use this connection.
there are some stepper drives that will work just fine with open collector screw terminal connections. I have seen many drives state in their respective manuals that they will work with open collector but in reality they do not perform well, when that same drive was moved to the 5 volt TTL db25 connection it ran like a dream. So the general advice is stepper drives should use the DB25 connector. That being said there are always exceptions to the rule.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
1metalguru
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Re: Basic hookup

Post by 1metalguru »

Hi guys:

Thanks all (cnckeith, richards, etc.). Appreciate your insights.

Can't help but notice that pretty much all stepper driver schematics show OC drive for the module. A few mention line drivers, but only if the distance from the driver to the stepper module is relatively far, or the device is located in a high noise environment. I am driving cables a few inches long, in a shielded box.

As this is a learning experience for me, I will do some testing once I get hardware in place.

MG
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Re: Basic hookup

Post by Richards »

Testing is the best way. You would think that driving simple stepper motors would be easy. The stepper motor driver has an opto-coupler input to isolate the input section from the output section. Nothing should be easier. But that's not how it works. A stepper driver is a chopper drive. It uses a high voltage to force current through the motor's windings and then "chops" the voltage down to 5V or less to keep the coil saturated. It can repeat that sequence 100,000 per second per drive. A stepper driver is basically an EMI generator. A switching power supply is another EMI generator. It uses high-speed switch circuits to generate the desired voltage. The VFD drive is another EMI generator. It too, uses high-speed switching. Put all those devices inside a closed cabinet and every wire inside that cabinet becomes an antenna. Fortunately, for most of us, if we use proper design methods, the system works reliably.
-Mike Richards
1metalguru
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Re: Basic hookup

Post by 1metalguru »

Hey Guys:

Another quick question. Couldn't find anything in the forums, but would it be possible to use the DB25 for driver module step and direction outputs, and the H2 and H3 Enable only outputs for the associated drivers? Enable is not a high speed output, it should work as long as the Acorn hardware updates the two sets of signals (DB25 and H2 and H3 outputs) pretty much simultaneously.

MG
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Re: Basic hookup

Post by suntravel »

1metalguru wrote: Mon Aug 15, 2022 5:10 pm Hey Guys:

Another quick question. Couldn't find anything in the forums, but would it be possible to use the DB25 for driver module step and direction outputs, and the H2 and H3 Enable only outputs for the associated drivers? Enable is not a high speed output, it should work as long as the Acorn hardware updates the two sets of signals (DB25 and H2 and H3 outputs) pretty much simultaneously.

MG
Normal wiring....

https://www.centroidcnc.com/dealersuppo ... 032.r2.pdf

Uwe
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