Plug-in interface for External stepper Drivers


Ken Hunter
 

This topic is in regard to creating a simple interface to OnStep that will allow
the use of External Stepper Drivers. Prior discussion can be observed
beginning at msg# 44661

Goals: 
1. Simple, self contained and powered adapter to provide 5VDC and
switched Ground returns for the External Driver Optocouplers.

2. Provide signal conditioning for DIRECTION, STEP, and MODE.

3. Low cost and easily duplicated. Parts required will be less
    expensive than shipping a completed unit (BUMMER) .

I have been considering a small footprint, 16 pin PCB following the
layout of a standard StepStick Stepper Driver such as the LV8729
etc that can provide 5VDC to the External Driver input+ connections
and Ground returns for the External Driver input- connections as
well as a DC level change to allow MODE switching during Slews etc.

Here is the proposed connections for the interface.

Kludge with 3 2N7000 MOSFET switches and a 5V regulator.
All mounted on a PCB that replaces the usual driver.

Kluge pins...
(1) ENable not used
(2) MS1 not used
(3) MS2 not used
(4) MS3   Q3 Source (Mode)
(5) Reset not used
(6) Sleep not used
(7) STEP Q2 Source
(8) DIR    Q1 Source
(9) GND   
(10) VDD 3.3V reference for MosFet Gates
(11) 1B     Q1 Drain to TB6600 DIR-
(12) 1A     Q2 Drain to TB6600 PUL-
(13) 2A     Q3 Drain to TB6600 Mode- (Modified EN+)
(14) 2B     5V Pullup to TB6600 + terminals
(15) GND 
(16) VMOT Q4 12V to 5V Reg

2N7000 case TO92 or SOT23-3L
78L05 case TO92 or L78L05ABUTR (SMD)

Modifications to TB6600...
Isolate the ENable+ terminal (Call it Mode-) and connect internally to the Dip
Switch 8uStep pin. The 3 Mode DipSwitches are set and internally pulled HIGH
for 32uSteps, bringing the 8uStep pin LOW shifts the External Driver Mode to
8uSteps.

Note...
I do not feel confident in using the EasyEDA program from start to finish but
we should be able to get many of these small PCBs on one larger PCB and
have scoring cuts so they can be easily separated. I just do not know how to
do that! I have enough Break-Strip pins, thru-hole 78L05 and 2N7000 on hand
for about 25 kits. Help with the EasyEDA program will be appreciated.


Howard Dutton
 

1. Does an optocoupler on our device hold any advantage to simply using transistors?  I'd say yes, since it isolates the microcontrollers signal lines.

2. Personally I'd like to see provision for the fault signal coming back from the stepper driver.  Perhaps a shunt/option to select between FLT or M2 (aka MS3, mode control output) on the third RJ45 output pin.  We could move the EN pin in software to M2 should the user want enable instead of mode control, avoids using a special/shared pin for EN.

3. Is having +5VDC really that important? adds cost vs. simply saying "use 24VDC" and having the resistors built in.


Howard Dutton
 

On Tue, Jun 14, 2022 at 03:49 AM, Ken Hunter wrote:
78L05 case TO92 or L78L05ABUTR (SMD)
It was pointed out to me that this might be a problem even at 12V (let alone 24V) as the current requirements of driving the 3x optocouplers is not insignificant.


mario rocha
 

Hi Kent Hunter,
Perhaps the expander driver - Ramps Mks Gen Tb6600 4.5A can be useful.


Greets,
Mario



Howard Dutton
 

On Tue, Jun 14, 2022 at 11:53 AM, mario rocha wrote:
Hi Kent Hunter,
Perhaps the expander driver - Ramps Mks Gen Tb6600 4.5A can be useful.
 
No good for us as our systems are mostly 3.3V and that doesn't seem to do the needed level conversion.  For a Mega2560/RAMPS fine as its already 5V but that's old slow h/w that were moving away from here.


John Petterson
 

I might be confused, but what kind of external drivers are you trying to interface to?  If it is something like this:

https://www.amazon.com/Twotrees-Stepper-Driver-TB6600-Controller/dp/B07PQ5KNKR

then the obvious quick solution should be this :

https://www.amazon.com/TWP-accessories-External-Switching-Microstep/dp/B072QTVLRK

And that price will be hard to beat building something - 4 pieces for $15 or $3.75 each. 

There is also this one for $1.68 each:

https://shop.lerdge.com/products/adapter-module

But is that what you are talking about?

John

 


adraasch
 

John,

That is an interesting module indeed.

This is the link to the product page from the manufacturer:

It shows that the module works with motor voltages ranging between 12 and 35 volts.
There appear to be three transistors and three large resistors.  The latter are likely what is being used to limit the optoisolator LED current in the external driver when up to 35 volt motor voltage is used.

I sent an email to the manufacturer's support email address requesting a schematic so we can review its design to make sure it is compatible with the various control motherboards in use by OnStep.

I'll let you know if I hear back from them.

Thanks,

Arlen

On Tue, Jun 14, 2022 at 11:00 PM John Petterson <j.petterson@...> wrote:

I might be confused, but what kind of external drivers are you trying to interface to?  If it is something like this:

https://www.amazon.com/Twotrees-Stepper-Driver-TB6600-Controller/dp/B07PQ5KNKR

then the obvious quick solution should be this :

https://www.amazon.com/TWP-accessories-External-Switching-Microstep/dp/B072QTVLRK

And that price will be hard to beat building something - 4 pieces for $15 or $3.75 each. 

There is also this one for $1.68 each:

https://shop.lerdge.com/products/adapter-module

But is that what you are talking about?

John

 


Ken Hunter
 

John...

Sherlock Holmes would be proud.
That seems to be exactly what we needed for the Hopewell Observatory.
Only thing now is somehow getting the Mode signals into the TB6600

Great find!


Ken Hunter
 

Some of the photos show the item marked 5V and 24V... I tried to contact the
Mfr on their Facebook page to ask about that. At that price, I'll have to order a
dozen or so to pass around.

Ordering direct at $1.65 each is better than Amazon at $15 for 4 devices.
They quote free shipping and MAYBE 3 day delivery.


kevin
 

On Wed, Jun 15, 2022 at 05:49 AM, adraasch wrote:
The latter are likely what is being used to limit the optoisolator LED current in the external driver when up to 35 volt motor voltage is used.
Interesting product i would like to see the circuit for it.
Note in the link  https://shop.lerdge.com/products/adapter-module  the top photos are labelled with 5V but the one with the wiring diagram and some of the lower photos  are labelled 24V. it is actually the motherboard Vmot pin.
the external driver is opto isolated so presumably they are using the pin labelled 24V for power and you can run your driver at a different voltage to the motherboard Vmot.
the resistors are marked 152 which is 1.5k, with a 24V on the Vmot pin and allowing 5 volts for the opt isolator and the drivers internal resistor the opto current would be about 13ma.
There is also a small resistor (presumably) marked 0  next to each Fet. I am not sure of its purpose but it may be there from an earlier design where it was populated or it could be used as a fuse?


kevin
 

forgot to add that if your motherboard Vmot is only 12V then the opto current would be down to about 5ma.


Howard Dutton
 

That's great, I knew I've seen similar but failed to locate them when I looked recently.


Howard Dutton
 

Still kind of a shame they don't bring the signals out on the 4 stepper motor pins.


Howard Dutton
 

On Wed, Jun 15, 2022 at 03:38 AM, kevin wrote:
the resistors are marked 152 which is 1.5k, with a 24V on the Vmot pin and allowing 5 volts for the opt isolator and the drivers internal resistor the opto current would be about 13ma.
The DM542 datasheet I read calls for using 1k at 12V and 2k at 24V.


Howard Dutton
 

On Wed, Jun 15, 2022 at 03:38 AM, kevin wrote:
Note in the link  https://shop.lerdge.com/products/adapter-module  the top photos are labelled with 5V but the one with the wiring diagram and some of the lower photos  are labelled 24V. it is actually the motherboard Vmot pin.
Strange, but they wouldn't have those 1.5k resistors if 5V were used.  Perhaps an earlier design they changed.


adraasch
 

The 0 ohm resistors are used sometimes as configuration jumpers, but in this case they are most likely a way of avoiding making a double sided circuit board.  When designing a PCB, if you need to "cross over" a circuit trace on a layer you can place a resistor that straddles the trace you want to "cross over".  The 0 ohm resistor is a short, so it behaves like a wire that jumps over the existing trace.

If you can avoid making any traces on one side of the PCB by using a few zero ohm resistors you can reduce the cost of the board as you will have a single sided board with no vias.

Best regards,

Arlen 

On Wed, Jun 15, 2022, 6:42 AM Howard Dutton <hjd1964@...> wrote:
Still kind of a shame they don't bring the signals out on the 4 stepper motor pins.


kevin
 

certainly a possible explination, i used to layout PCBs by hand with sticky circles and crepe tape (brady)  and it is surprisingly hard to do even a simple circuit on a single side without jumpers. https://en.wikipedia.org/wiki/Three_utilities_problem


Guy Brandenburg
 

What about using this module here?

https://github.com/bdring/external_stepper_motor_driver

, which capitalizes Weirdly & misinterprets words just To keep you on your toes

--
Guy Brandenburg

President, The Hopewell Observatory
www.GuysMathAstro.com


Robert Benward
 

Seems we are running parallel threads.  See Howard's "Slipstick" message.

The board on github is only problematic if you want to use only a single supply, and it needs to be a high voltage, >32V or so.  Dissipation in that linear regulator needs to be watched.  Otherwise, power the Onstep with 12V, and use another robust higher voltage (>24V) supply for the external TB6600 (or equiv).  This looks like a good solution.

No one is providing a schematic for these devices linked in the pervious message.  The one on the Lerdge site shows both the 5V and 24V version.  I can only suspect the 1500 ohm resistor on the bottom are in series with the driver opto couplers.  If that is the case, those values are too high for a 5V variant, but OK for a 12V variant.  See above regarding two supplies.

Bob


John Petterson
 

There is one more , this one from India:

https://robu.in/product/mks-cd-v1-0-external-stepper-driver-interfacing-module/

At today's exchange rate that one is about $3.83 each.  Looks like a different circuit, this may have optoisolator instead of transistors.

John