laser diode is slighly on during axis moves

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28 Mar 2023 04:05 #267665 by ericg
yes it sounds vague, but that's what's happening, the laser is connected to hm2_5i25.0.pwmgen.01...... and outputs appear on hm2_5i25.0.gpio.018.....
I am getting very light burning between movements of the head when the laser is commanded to be off (M68 E0 Q0)
it appears that there is small voltage fluctuations coming from the 5i25 P2 output whenever other pins are active, ie moving a joint.
I tried inverting the gpio but that put the laser on at max power, I tried a 470R resistor as a pull down on the pin (14 on P2) and that had no effect
other than this annoyance, everything is working fine.
so can anyone suggest why I get small voltage fluctuations on this output and can anything be done about it?
I can post my configs if that would help.
Eric

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28 Mar 2023 06:51 #267669 by robertspark
have you run the wiring next to the stepper. wiring?

it may be inductance

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28 Mar 2023 07:02 #267670 by ericg
no I don't think so as I checked the output from P2 at the DB25 breakout board at the end of the DB25 cable from the 5i25 and it was jumping around even when the cable to the laser was disconnected. It seems to be steady at 0.5v when no joints are moving and the laser is off at that voltage and jumping up to 0.85v approx when I move a joint. giving a weak laser beam and that is causing the light burning when focused on the material.
I will however double check the layout, thanks for the thought

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28 Mar 2023 08:59 #267681 by robertspark
given you are using PWMGEN, what have you set the other pins at for the pwmgen?

linuxcnc.org/docs/devel/html/man/man9/hostmot2.9.html#pwmgen

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28 Mar 2023 12:30 #267693 by tommylight
Pwm cable from Mesa to laser module must be shielded if it is longer than say a meter. I would use shielded for any length, shield wired to ground on the box only on the controller side, leave shield on the laser side unconnected.
Power supplies will cause that, try to find an old laptop/ptinter/access poit/monitor power brick, those are properly shielded.
A friend had the same issue, just changing power supply fixed it.

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28 Mar 2023 15:43 #267701 by PCW
My guess is that there is significant high frequency current flowing
in the 5I25 ground return. This may be from the step drives or a
switching power supply. This may be caused by not having a
single point ground.

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28 Mar 2023 22:49 - 28 Mar 2023 22:50 #267737 by ericg
Thanks for the replies, the relevant setting are
in main .hal file
setp hm2_5i25.0.pwmgen.pwm_frequency 50 (cannot remember why I selected 50 just a balance between spindle and laser requirements I think)
in laser.hal file
setp hm2_5i25.0.pwmgen.01.output-type 1
setp hm2_5i25.0.pwmgen.01.scale 100

but I do have switching PSU's, 38v and 12v ones, I'll check these out and replace with analogue ones if required.
I will also check my grounding although I have a busbar as common ground, I will also look at my shielding to see if I've missed something.
So I'm assuming from all these comments, no one thinks it's a 5i25 inherent issue?
thanks for the feedback
Last edit: 28 Mar 2023 22:50 by ericg. Reason: spelling fix

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28 Mar 2023 23:08 - 28 Mar 2023 23:10 #267739 by PCW
One thing you can do to lower HF ground currents is to put common mode chokes
( basically large ferrite beads) on the step motor leads (one bead over all 4 wires near
the driver) and the output pair (+ and -) of the step drive switching supply.

Line filters on the power supply inputs can also help.
Last edit: 28 Mar 2023 23:10 by PCW.

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29 Mar 2023 01:14 #267748 by ericg
started looking for missing/faulty earths so I was looking inside my control box with power off (of course) when I noticed the 12v switching psu for the laser, it's power on LED was blinking on every 20 seconds, that was odd so I disconnected all my cables except for the power lead and it still happened, I pulled it out to do more checking on the bench with a different power cable and it did not happen, put it back and it did happen, replaced the power lead with a heavier spare one, put everything back together and all the issues disappeared, the P2 pin was now showing 20mV and did not jump around with joint movements. Tested the old power lead and it appears fine, so other than having a lightweight cable replaced nothing else has changed.
Seems weird to me.
Thanks for everyone's input.

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29 Mar 2023 01:22 #267751 by ericg
good thoughts, re the ferrites and line filters, I think I have some of those in my boxes of electronics stuff somewhere, I'll add them for good measure.
Eric
The following user(s) said Thank You: tommylight

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