[H500]

If you connect the input diode anodes to V+ and drive the cathodes, you likely won't need the transistors at the output. Just pull the collectors up with the 3k3 resistors.

[Mike4703]

Do you mean like this? I reposted the original schematic with the output transistors to correct the second input diode orientation. What do the output transistors do? Increase the gain and/or maintain pulse phase?

[H500]

The 200ohm and 1n should be moved to the driven pin, although your circuit will probably work. I actually think you can remove them and still have no problem. The transistors primarily re-invert the signal.

[Mike4703]

Ok wired up a little prototype optoisolator board using the final schematic and connected it between the interface board and the stepper driver. +5v is available from the interface board and that was used for the interface side of the optoisolator circuit, but it's main power supply is the same 24v one that is also connected to the driver boards. I connected a separate power supply to the driver side of the optoisolator board. I just connected one channel up using the x-axis and then manually drove the x-axis from the controller. No movement of the x-axis. I connected my ocilloscope to the step out of the optoisolator board and the output looked identical to the output of the interface board, yet was not triggering the driver. The manual for the G251X drivers says this about the step input: These terminals can be driven with 3.3V or 5V logic. If 3.3V logic is used then the input current is -1mA for logic "0" and zero for logic "1". If 5V logic is used then the input current is -1mA for "0" logic and 0.67mA for logic "1". What's wrong here? The scope seems to indicate that the pulses are positive. Does the -1mA current requirement mean that the voltage has to be negative? Is the output of the two different schematics different from the driver input requirement point of view? Maybe I do need the transistors to reinvert the signal. Unless someone can tell me for sure, I will go ahead and build the circuit with the output transistors and try it, but if its something with grounding or power supply that can be changed, let me know.

[H500]

Is the scope trace taken with the g251 connected? If so, the signal looks OK. Adding transistors shouldn't make a difference.

Does the g251 have an enable pin that needs to be connected?

[Mike4703]

Yes the G251 was connected when the tracing was made. The G251 has no enable pin only a disable pin that is left unconnected. It disables the drive output when connected to ground. So this should have been a good test of the circuit but absolutely no reaction from the x-axis stepper. All the other axis moved normally with the direct connections. I already modified the test board and added the transistors back in anyway, so I'll test it that way again tomorrow and see what happens.

[H500]

Try pulling the disable pin high just in case.

The procedure I would use is
1. Bypass the circuit to make sure the motors still work.
2. Check output. I can't tell from your trace whether the low is low enough.
Voltage when high. Must be above 2v (or whatever Geckodrive specifies)
Voltage when low. Must be below .8v

If both conditions are met, your motor should move. Digital signals are not mysterious. There's nothing more other than rise/fall times and frequency, but those looks acceptable from your trace.

3. You could also compare the input to the output. They should look similar.

[H500]

I have a breadboard with essentially the same circuit. It uses 150 ohm, no parallel capacitor and 3k3. I hooked it up to my driver and it works fine with Mach 3.

[Mike4703]

I just got my prototype to work also. The one with the output transistors. There was rough running until I remembered to connect the pin 12 logic ground to the new ground on the output side of the optoisolator board. At that point the x-axis stepper ran exactly like it did when directly connected. Very fast and smooth. The other axis were unaffected of course but I checked their movement anyway.Because I connected and took down this circuit and the previous one without the output transistors a couple of times there is no way I can absolutely be certain that the previous failure was not caused by me forgetting something, like switching the logic ground connection. But anyway the thing works and works well. If nothing else I'm learning more electronics. I am posting photos and video. Please excuse my "rats nest." When I get the final optoisolation board build I will work on a final enclosure for all of this. What kind of driver are you using and how are the "grounds" or "commons" or negative hooked up? I still get confused by this topic. For my test I used a completely separate power supply for the output section (yellow box in background of first photo), but would like to build a small power supply into the final optoisolator board. Like you say this should be straight forward but I am unexperienced and very nervious about burning something up again. Using your simpler design on the final board would be nice. I'll try your design again before going on to the final board design.

[Mike4703]

I needed a break from board design so I tried running the mill under program control for the first time using a rectangular slot routine built into the DSP control. Can't believe this is working. The prototype x-axis optoisolation is in use, but the rest of the axis are connected directly. I tried to upload a video of this but it won't go. I think it's too big.

[H500]

I am working on a drive of my own design. Actually, the design was done by Mr Mariss Geckodrive. I posted my version in the Open Source Controller section.

If you build a power supply for your opto board, its output ground needs to be connected to pin 12 of the g251.

In order to have full isolation, the input side must have its own power supply, with the ground NOT connected to the output side ground.

What DSP controller are you using?

[Mike4703]

This controller is made by RichNC in Beijing. It is sold directly by them and also by MotionTek in Canada, and by Motion Control Products in England and probably others as it is shipped with a lot of Chinese CNC routers. The original part number is RZNC-0501 but is called MO-CON501 by the English company which has the best documentation on it. I'll go take a look at your design. I don't need drivers right now but I'm learning all I can while I'm at it.

[H500]

Interesting. Another toy to build!

[Mike4703]

Check out the Chinese companies website RZNC-0501,RZNC CNC Controller,RICHNC Drive,RICHNC Motor-Beijing RichNC Technology Co.,Ltd. first. This controller is only the most basic of many varieties that they make and the direct purchase from them is about half of what everyone else wants for these. Wish I'd known that before I bought mine.

[Mike4703]

Here is a link to the video of my mill running completely under program control for the first time. It is running a built in rountine for cutting a rectangular slot. I don't dare try running a G code program until all the safety equiptment is intalled. The more time I put into this the more cautious I get. The optoisolation board is all wired up now and I'm working on the power supply for the output side, and then have to install and connect up. A lot to do yet but seeing this thing run like this really felt like I was getting somewhere. [ame="http://www.youtube.com/watch?v=5fO-CVflo94"]‪Progam Control w DSP.MPG‬‏ - YouTube[/ame]

[H500]

Looks good! I can't wait to get my machine to the same stage.

Did you verify that there is no missing/extra steps? Lucas from my open source thread, mentioned that the opto circuit with the transistors was designed by Mariss to address certain issues found with the simple circuit. So you should probably ignore my comments about not needing the transistors unless you verified it for yourself. My quick testing on a breadboard indicated that the simple circuit resulted in missing steps.

[Mike4703]

Thanks for the info. I did go ahead and build the board with the transistors as per Mariss original design, mostly because I had already bought the transistors and pullup resistors, so I'm glad I did. I would think I would have noticed missing or extra steps at very low speeds but maybe not. What's the best way to test for this? As soon as the final board is finished in a couple of days I will do a careful calibration to make sure that the machine is moving exactly the same distance as is being input into the controller. This has to be done anyway to make sure the pulse equivalent settings are correct but should also reveal any inconsistency in stepping. How's your machine coming along? It took me about two hours to review all the material in your open source thread and another on a rotory table indexer. This is a little over my head, which is why I finally just bought the gecko 251x drives. I'd could use the rotory table indexer though. Sherline wants almost $600 to buy theirs which I'm not going to do--so maybe this is next.

[H500]

The 251s are excellent drives. If I didn't enjoy learning how to design my own, I would buy those.

My machine is far from ready. I have the x and y axis ball screw mechanism done, but I would like to experiment with a DSP based board before I settle on which to use. I will have more time during the colder months. Summers are short here, so I don't want to squander the nice weather by being indoors all the time.

I test for missing steps by marking the rotor position and then step 1000 or more complete revs in one direction. It should stop exactly at the mark.

[Mike4703]

Completed the board today. Good news is that the optoisolation works fine. Bad news is that I shorted the outputs on two of the drivers and they no longer are working. Next step is to ask Gecko if it would be cheaper for them to be repaired or replaced. The problem was I was trying to save money by recycling the output plugs from the old TB6560 board. (See Photos) I checked for shorts with MM before soldering but after mounting and fitting into the tight space at the edge of the board two shorts developed in the connections at the extreme ends of the board.

[H500]

If this is the first time you killed a Geckodrive, I believe they will replace them for you no matter whose fault it was. But you can only make the request once in a lifetime.