Laser pwm low power

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11 Aug 2019 15:10 #141916 by brettw
Laser pwm low power was created by brettw
I am trying to install a laser on my cnc machine. I have tried linuxCNC 2.7.14 and updated to 2.8 and have same issue. I am using a sainsmart breakout board. Using pin 16( have also tried different pins) and a postprocessor for vcarve from jtech photonics. The gcode will turn laser on and off but it is low power. With the laser hooked to +5 volts it works like it is supposed to. Everything was setup in stepconfig using pwm setting. Only thing I can figure is perhaps the parallel port( onboard dell dimension 4600) maybe 3.3 volt instead of 5 volt. Any help will be appreciated.

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11 Aug 2019 18:09 #141924 by PCW
Replied by PCW on topic Laser pwm low power
If you are using the Sainsmart breakout , the output are driven by 5V powered buffers so
you should have 5V swing on the outputs regardless of whether the parallel port is 3.3V or 5V

You should be able to verify this with a voltmeter (with PWM set fo 0 and 100%)

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13 Aug 2019 18:42 #142069 by andypugh
Replied by andypugh on topic Laser pwm low power
My guess would that this is an issue with the pwm scaling factor.

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13 Aug 2019 20:25 #142078 by brettw
Replied by brettw on topic Laser pwm low power
Any clue how to correct this?

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13 Aug 2019 22:31 #142090 by andypugh
Replied by andypugh on topic Laser pwm low power
Change the scaling factor in the HAL file.

Can you post your HAL file? It will make it easier to speculate.

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20 Aug 2019 00:37 #142528 by brettw
Replied by brettw on topic Laser pwm low power
This is the hal file I am using. Sorry to be so slow getting it posted. Been super busy with work and anniversary.

File Attachment:

File Name: gatton.hal
File Size:4 KB
Attachments:

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20 Aug 2019 00:42 #142529 by brettw
Replied by brettw on topic Laser pwm low power
I have also checked the pwm pin with a voltmeter. Without the laser hooked up I get 5 volts using s1000 m3. With laser hooked up and on the same code only gives me 3.92 volts. The laser works when hooked up to the +5 volt pin and will actually make some smoke. It acts like the pwm is low power and laser is just a blue light when connected to the pwm pin. Thanks for any help.

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27 Aug 2019 21:42 #143363 by andypugh
Replied by andypugh on topic Laser pwm low power
It sounds like the laser input pin is taking significant current.

What is the PWM-to-voltage conversion stage? Maybe you need a buffer? (op-amp as voltage follower is one option)

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27 Aug 2019 23:58 #143379 by brettw
Replied by brettw on topic Laser pwm low power
Andy I am new to linuxCNC and really have no clue what you are asking. I did place a couple pull up resistors between my pwm pin and the +5 volt pin on my breakout board. Thought that would improve my voltage but made no change. I am at a loss as what to try next. Thanks

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28 Aug 2019 00:33 - 28 Aug 2019 00:33 #143380 by andypugh
Replied by andypugh on topic Laser pwm low power
It might be that the BoB can't supply as much current as the laser input stage requires.

But first, can you make sure that the PWN duty cycle is 100%?
Look at the pin pwmgen.N.curr−dc with halmeter and check that it is +1.0
Last edit: 28 Aug 2019 00:33 by andypugh.

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