UCBB and +5v to stepper drives?

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UCBB and +5v to stepper drives?

Postby rowka » Sun Jun 28, 2020 4:27 pm

Can I pull the +5v for my stepper drivers (Geckodrive 201x) directly from my 5v ps that supplies the UC300eth, or does it need to come off the UCBB?
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Re: UCBB and +5v to stepper drives?

Postby cncdrive » Sun Jun 28, 2020 8:27 pm

No you should not do that, because that 5V powers the UC300ETH and the logic part of the UCBB.
If you use that to power the stepper drives with step/dir signals from the UCBB that means that you have to common the ground of that power supply with the isolated 12/24V power supply,
to make the output transistors emitter of the UCBB referenced to your 5V powersupply's ground (0 Volts).
This breaks the isoation of the UCBB, because then your outputs which are to be powered from a separate 12 to 24V PSU will share the same ground as the ground of the UC300ETH.
So, then the UCBB will loose it's purpose of isolating the I/O signals between the environment and the UC300ETH.

You should use a separate 5V power supply or you can use the 12 to 24V power supply which you using for the I/Os of the UCBB anyways.
You could step down that 12 to 24Volts to 5V with a step down switching regulator or LDO.
Or you could use series resistors, 2kOhms should be fine for 24Volts, the series resistors will limit/set the current for the step dir signals getting into the drives. (I'm assuming the drives have optoisolator inputs.)
Or you could connect the step/dir signals directly to the UC300ETH output pins. I'm again assuming that the drives have optoisolator inputs, then there is no need for isolating them with the UCBB, because the signals are isolated in the drive with the input optocouplers.
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Re: UCBB and +5v to stepper drives?

Postby rowka » Sun Jun 28, 2020 9:11 pm

I'm not sure I understand.
I have one 5v ps that powers UC300ETH which then feed through to the UCBB.
I hqve one 24v PS that powers the UCBB.

The UCBB manual on page 9 says:
To connect the step and direction signals to stepper or servo drives any of the 16 outputs can be
used. Most stepper drives have an optocoupler on these signals with a series resistor fitted in series
with the LED of the optocoupler. Mostly the series resistor's value fits a certain voltage level or
voltage range, usually it is around 5Volts. With these drives the 5Volts from the screw terminals 3.
and 4. can be used to drive the step and direction lines of the drives as shown on the following
picture:

and the picture on page 10 clearly shows 5v coming from the UBCC.

The Geckodrive has only 3 inputs. Step Direction Common
Their manual says:
STEP AND DIRECTION INPUTS

TERMINAL 8
Direction

Connect the DIRECTION line to this terminal.

TERMINAL 9 Step

Connect the STEP line to this terminal.

TERMINAL 10 Common

Connect the controller’s +3.3VDC, +5VDC or GND to this terminal.

These inputs are optically isolated from the rest of the drive. Terminal 10 is the common connection for the opto-isolators and must be connected to the +3.3VDC, +5VDC or GND of your indexer or pulse generator.

These inputs are meant to be driven by 3.3V to 5.5V logic capable of sourcing or sinking 2.5mA of current. The minimum logic “0” time is .5uS while the minimum logic “1” time is 3uS with 3.3V – 5V connected on the COMMON terminal. The minimum logic “0” time is 3uS while the minimum logic “1” time is 0.5uS when connected to GND on the COMMON terminal. Microstepping occurs on the falling edge of the step input when COMMON is a positive voltage and on the rising edge when COMMON is connected to GND and on the rising edge when connected to 3.3V – 5V.


My intent was to send UBCC outputs to Step and Direction and connect UBCC 5v to the drive's "Common."

Here is a link to the whole manual for the Geckodrive G201X stepper drive:
https://www.geckodrive.com/support/g201x-g210x-rev-6.html

Id=s this plan what you are saying?
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Re: UCBB and +5v to stepper drives?

Postby cncdrive » Sun Jun 28, 2020 10:58 pm

The 5Volts which powers the UC300ETH and is fed through the ribbon cable to the UCBB powers the isolated side of the UCBB.
There are optical isolator ICs on the board which isolated the signals between the environment and the logic part of the UCBB which is the UC300ETH side of the isolation barrier.
This is why you need a separate 12 to 24V power supply for the I/Os of the UCBB, because that powers the other side of the isolators, the relays, buttons, switches etc, which you connect to the board.

If you want to switch the 5Volts which powers the UC300ETH with the UCBB then for that you have to connect the ground (0 Volts) of that power supply to the ground of the transistors which is the 24V0 terminal on the UCBB,
otherwise your 5V will be floating as there is no connection to the isolated side of the UCBB this could even damage the output transistors on your UCBB, but even in best case the outputs will not work, will not switch your 5Volts if the 5V power supply is not common grounded.
And common grounding is a problem, because you bypass the isolation barrier connecting the 5V0 and 24V0 grounds together. This is totally unrecommended.

So, again, you can use a separate 5V power supply. Or you can create 5Volts from the 12 to 24V powersupply which you using on the UCBB to power the isolated side.
Or you could use series resistors to limit the current into the optocoupler input of the drive.
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Re: UCBB and +5v to stepper drives?

Postby rowka » Sun Jun 28, 2020 11:05 pm

Okay. So ignore the 5v power supply.

I can use the 5v generated by the UBCC on pins 3 and 4 for the stepper driver? Yes? This is how it is designed to work?
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Re: UCBB and +5v to stepper drives?

Postby cncdrive » Mon Jun 29, 2020 12:02 am

Yes, you can use that 5Volts which is available on pins 3. and 4. of the UCBB.
I thought you asking about using the 5Volts which powers the UC300ETH, you should not use that.
These are 2 different Voltages.
The 5V on pin 3. and 4. on the UCBB pins is generated from the 24V power supply of the UCBB and so you can use that for the step/dir signals as drawn in point 5.1.3. of the UCBB manual.
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Re: UCBB and +5v to stepper drives?

Postby rowka » Mon Jun 29, 2020 12:23 am

Yes. Thank you.

That’s what I needed to know.

Use pins 3 and 4. All good!
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