Output voltage breakout board

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13 Sep 2019 09:27 #145038 by CNC_build
Hello everyone,

I am in the process of getting one of these cheap 5 axis boards from eBay to run.

One major problem is output voltage of the board.

I am using a Lenovo T42 laptop.
The voltage directly at the lpt port is 3.3v.
After 3m of lpt cable it's still at 3.3v.

The problem is that the bob only puts out 2v.

So far I got the motor to turn, change direction and homing with an inductive sensor also works.

But this is just on the desk. I have major concerns that it will run reliable once it's installed at the machine with cable lengths of more than 3m.

It is supposed to run JMC 180W Servo motors so the step pulses will run through the servo cable and there will be a 2.2kw vfd driven spindle as well. All cables will be shielded of course and separated as far as possible from each other in the cable chain.

Has anyone encountered similar problems with this kind of board?
Is there any way to raise the lpt voltage, I couldn't find any settings in bios for that so far...

Thank you in advance
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13 Sep 2019 10:10 #145044 by tommylight
The break out board does not output any voltage ( well most of them don't ), so what you are measuring as 2V is the drop in the photo transistor inside the optocouplers .
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13 Sep 2019 12:30 #145055 by CNC_build
Hello tommylight,

Thank you for your help.
I do think this board outputs voltage.
It seems like it takes the voltage from the USB connector and amplifies the control signals with it.
Once I connected usb power, the voltage for direction pin 3 was up at 5 volts. Also the relais only seems to work if usb power is supplied. This behaviour might be caused by the laptops low lpt voltage levels.

Also the voltage for the step pulses increased to 5v, even though the signal is not super crisp.

I think I will give the board a try, the intended mill is no super fast performer as it has a moving gantry. The fixed gantry mill will be controlled by a proper 7i76e.
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13 Sep 2019 12:43 - 13 Sep 2019 12:43 #145056 by Clive s
These bobs require either 5V from the usb or 5v put in on the 5v input terminals .

They also require 12-24v put in order for the inputs and spindle speed 0-10v to work
Last edit: 13 Sep 2019 12:43 by Clive s.
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